GB1584091A

GB1584091A - Device for indicating the working state of a hydraulic actuator

Info

Publication number: GB1584091A
Application number: GB35731/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-09-01
Filing date: 1977-08-25
Publication date: 1981-02-04
Also published as: NO151056B; DK152149C; DK152149B; DE2723935C2; NO151056C; DE2723935A1; NO772939L; DK395776A

Description

(54) A DEVICE FOR INDICATING THE WORKING STATE OF A HYDRAULIC ACTUATOR (71) I, CARL ORLA HANSEN, a citizen of Denmark, of No. 12 Laesvej, 4700 NAESTVED, Denmark, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed to be particularly described in and by the following statement: The invention relates to a device for indicating the working state of a hydraulic actuator of the kind having a movable member movable between a closed position and an open position under pressure of oil supplied through at least one control oil line and with which there is also associated a low pressure oil line.

In hydraulic control systems, in which a number of hydraulic actuators are operated through pipe lines from a control panel, a need often exists for feed back information from each actuator to the control panel about the working state of the actuator.

Such feed back information may be obtained in many ways, such as electrically, by means of micro switches or potentiometers or hydraulically or pneumatically by means of pressure reduction valves or the like. However, common to these solutions is the necessity of one or more additional connections in the form of electrical wires or further pipe lines from the actuator to the control panel, at which registration of the feed back information is desired. Particularly in systems, in which there are great distances between actuators and control panel, quite consierable costs will result therefrom.

Feed back information may also be obtained by means of a flow measuring device measuring the amount of oil flowing out into the control oil line towards an actuator when it is opened. This method requires no additional lines, but like the methods mentioned above, it is relatively expensive due to the costs of flow measuring devices. Moreover, it will only give reasonably reliable results in systems having rather large actuators, because a flow measuring device will measure the total amount of oil flowing out into the control oil line during opening of an actuator, and this total amount of oil comprises, in addition to the opening volume of the actuator, also oil quantity contributions for filling the control oil line and the compression of oil and air, which may possibly be present in the control oil line.In systems having relatively small actuators, the two last mentioned dontribu- tions will often be of the same order of magnitude as the opening volume of the actuator, and, therefore, the method is unsuitable for such applications.

In hydraulic control systems there will usually be connected one or two control oil lines to each actuator. Two control oil lines are used when the actuator has two connections for pressure oil, and the movable member of the actuator is operated by pressure in one or the other control oil line, whereas the line which is not under pressure, is connected to an oil tank.

One control oil line is used when the actuator has two connections, one of which is always under pressure from a common circular line for a number of actuators, whereas the other is connected to the control oil line. When the control oil line is connected to the tank, the actuator will be closed by means of pressure oil from the circular line. When the control oil line has been brought under pressure, the actuator will open. Similarly, one control oil line is used, if the movement of the movable member of the actuator in one direction is caused by a spring, whereas the movement in the other direction takes place by means of pressure oil through the control oil line.

In marine installations, in which the actuators may be exposed to heavy corrosion through the action of sea water etc., it will usually be advantageous, in addition, to supply low pressure oil to the actuator casings through a similar circular line in order to keep them under a certain overpressure with a lubricant.

In respect of systems of the kind, in which two control oil lines for pressure oil are connected to each actuator, a position indicator device is known from German published specification No. 2,237,244, by which there has been provided between the pressure line and the return line a communication having a smaller cross-sectional area than said control oil lines, for example in the form of an axial bore in the slide valve of the actuator itself, which communication is kept open during the adjusting movement of the movable member of the actuator, but is closed in the end positions of this movable member. Such a device will not be usable in case of actuators having only one control oil line.

Furthermore, in this known construction, it is prescribed that the amount of oil flowing through said communication should be limited by reducing a flow slit by means of a throttle screw. However, since the working pressure and, as a result thereof, the difference pressure across said slit may be rather great, the slit must be so small that it becomes sensitive to dust and dirt, and, thereby, runs the risk of being stopped, whereby remote indication of the position of the movable member of the actuator is made impossible.

Taking as a starting point, systems of the kind in which there is associated with each actuator in addition to at least one control oil line, a common low pressure oil line of the above mentioned kind, it is the object of the invention to provide an indicator device, for indicating the working state of an actuator, which does not require additional line connections from the control panel to the actuator and may be used in case of actuators having both one or two control oil lines, and by which information may be obtained in the case that the movable member of the actuator has been blocked for one reason or the other, although the member has been actuated for movement, whether such blocking takes place in one of the end positions or an intermediate position.

According to the invention, this is accomplished in that there is provided between the control oil line or one of the control lines and the low pressure oil line a controllable by-pass valve which is controlled in dependence on the position of the movable member of the actuator in such a manner that passage of oil through the by-pass valve is prevented when the movable member is in the fully open position with working pressure in said control oil line or in the fully closed position with no pressure in said control oil line whereas oil is allowed to flow through the by-pass valve at a low flow rate, substantially independent of the direction of flow of oil between said control oil line and the low pressure oil line, when the movable member is in any position other than the fully open or fully closed position or when the movable member is in the fully open position with no pressure in said control oil line or in the fully closed position with working pressure in said control oil line, the said oil flow operating an indicator device arranged in communication with said control oil line at a location remote from the actuator.

When the actuator is operating correctly, said by-pass valve will be closed in the fully open position of the actuator with working pressure in said control oil line and in the fully closed position with no pressure in said control oil line, whereas in any intermediate position between said fully open and fully closed positions and, furthermore, if the pressure in said control oil line drops to zero in the fully open position of the actuator or increases to full working pressure in the fully closed position of the actuator, oil will be allowed to flow through said control oil line to operate said indicator device.

Installation of the indicator device according to the invention does only require the provision of said adjustable by-pass valve between one control oil line and the low pressure oil line, both of which will usually be present beforehand, and arrangement of the indicator device. In systems having no low pressure oil line, there must furthermore be added such a line which, however, will be common to a great number of actuators, and, therefore, represents only a modest additional cost. In systems having only one control oil line, oil may flow in both directions through the control oil line to actuate the indicator device. In systems having two control oil lines in addition to a low pressure oil line, the by-pass valve will be between only one control oil line and the low pressure oil line, and the indicator device will be connected to the control oil line communicating with the by-pass valve.

In a preferred embodiment of the invention, the by-pass valve is regulated by an arrangement of spring-loaded non-return valve members in an operator valve mounted on the actuator casing and connected with the control oil line as well as the low pressure oil line, said operator valve comprising actuating means for said nonreturn valve members controlled by the position of the movable member of the actuator. Thereby, the by-pass valve may be mounted in direct connection with a hydraulic actuator in a simple manner.

In this embodiment, said actuating means may comprise a spring-loaded pressure pin, which is displaceably mounted in the operator valve and projects with one end out of said valve to engage a curve member connected with the movable member of the actuator and having off-set contacting faces for said one end of the pressure pin corresponding to fully open and fully closed actuator and intermediate positions of the movable member of the actuator.

If said curve member is formed with a number of cut-outs to engage said one end of the pressure pin at fully open actuator and in a number of discrete intermediate positions of the movable member of the actuator between the end positions corresponding to fully open and fully closed actuator, there may in addition to the feedback information in a simple manner be obtained the possibility of securing the movable member of the actuator in such intermediate positions, even by actuators in which no proportionality exists between the positions of the movable member and the oil pressure in the control oil line due to engagement between one of said cut-outs and the spring loaded pressure pin.

The indicator device may be constituted by an indicator valve arranged in the control oil line betwen the actuator and a control valve for switching the actuator between closing and opening, said indicator valve comprising a flow cylinder constituting a portion of the control oil line and a springloaded slide valve displaceably arranged in said cylinder and assuming a rest position in case of no oil flow through the control oil line, said slide valve being movable, by oil flow in the control oil line out of said rest position in one direction or the other dependent on the flow direction.

In connection with such an indicator valve, feed-back information may be obtained in a simple manner in that said slide valve is extended outside said indicator valve to directly visually indicate whether it assumes its rest position or has been removed away therefrom in one direction or the other.

However, electrical feed-back information may also be obtained for example by means of one or more lamps in that an operating member for electrical indicating means to indicate that the slide valve does not assume its rest position is mounted in said indicator valve in communication with said slide valve to be activated by the movement of the said slide valve in one or the other direction out of said rest position.

In systems of the kind, in which the actuators are opened against a variable closing force, such as a spring force, or an accumulated, for example pneumatic pressure, and wherein the necessary opening pressure will be dependent on the actual position of the actuator, and a certain minimum pressure will be required to displace the movable member of the actuator away from the fully closed position, the operator valve mentioned in the foregoing may still be used while the indicator device may be constituted in a simple manner by a manometer arranged in communication with the control oil line and replacing the above-mentioned indicator valve.

While normally the feed-back information is obtained solely as an indication of the fact tht the actuator is performing an adjusting movement or intendedly or unintendedly assumes one or the other of the end positions, there may be obtained in a simple manner in systems of the last mentioned kind and by use of an operator valve having actuating means in the form of a pressure pin engaging a curve member as explained above, direct feed-back information on whether the movable member of the actuator occupies any one of said intermediate positions.

In the following the invention will be further explained by way of example, with reference to the schematical drawings, in which: Figures 1 and 2 are block diagrams showing different hydraulic control systems with a single actuator, and an indicator device according to th invention; Figure 3 is a longitudinal sectional view of an embodiment of an operator valve; Figures 4 and 5 are a longitudinal sectional view and a cross-sectional view, respectively, of an embodiment of an indicator valve; Figures 6 and 7 show alternative embodiments of hydraulic control systems incorporating a working state indicator device according to the invention; Figure 8 shows a modification of the operator valve for use in a system as shown in Figure 6 or 7; and Figure 9 shows. a further embodiment of an indicator valve with associated switch actuating means.

In Figures 1 and 2, two different embodiments of a hydraulic control system using a device according to the invention are shown. For the sake of clarity, only a single hydraulic actuator 1 is shown in both figurs, which actuator may be of a construction known per se and comprises a movable member which may be a rotatable or axially displaceable slide valve which be operating the actuator actuates the machine element, such as a valve spindle, which is to be operated by the actuator.

In the system shown in Figure 1, the hydraulic pressure medium, which is usually oil, is supplied to the actuator 1 through a single control oil line 2, the oil supply for actuating or opening the actuator 1 being provided by means of a control valve 3 symbolically shown, which has connection on one hand to a pipe line for oil under working pressure and is connected, on the other hand, to a return line, since the single control oil line 2 serves both as supply line and return line for control oil to the actuator 1. In the position shown in Figure 1, the control valve 3 has been operated to supply control oil for opening the actuator 1. If the control valve 3 is switched by movement towards the left in Figure 1, the control oil line 2 will be alternatively connected to the return line.

Usually, a hydaulic control system of this kind will comprise a considerable number of actuators as shown at 1, with associated control valves as shown at 3, and these control valves may be positioned at a relatively great distance from the actuators in connection with a common control panel.

Furthermore, it is assumed that there is associated with a control system, in which a working state indicator device according to the invention may be used, a low pressure oil line 4 common to a number of actuators, through which line the actuator casings may be supplied with low pressure oil to keep them under a certain over-pressure by a lubricant, if so desired, in view of corrosion, for example. As mentioned in the foregoing, such a low-pressure oil line may have the form of a common circular line.

In order to obtain feed-back information on the working state of the actuator 1 to the common control panel, which may as mentioned be positioned in great distance from the actuator, there is provided, according to the invention, between the control oil line 2 and the low-pressure oil line 4 an adjustable by-pass valve 5, which in the fully open and fully closed positions of the actuator 1 and with working pressure and no pressure, respectively, in the control oil line is closed to oil passage, but in any other position of the movable member of the actuator 1, and if, in case of open actuator, there is no pressure in the control oil line 2, or in case of closed actuator, working pressure exists in the control oil line 2, allows passage of a small amount of oil between the control oil line 2 and the low pressure oil line 4 for operating an indicator device 6 which is arranged in communication with the control oil line 2 remote from the actuator 1, for example at the common control panel to provide specific indications of such conditions.

In the system shown in Figure 2, supply of control oil to an actuator 7 takes place through separate control oil lines 8 and 9 by operating a control valve as shown symbolically at 10, dependent on the fact whether the actuator is to be opened or closed, one control oil line being brought under pressure and the other being connected to the tank through the return line. In this system which may otherwise be constructed in the same manner as the system shown in Figure 1, the by-pass valve 5 is arranged between the low pressure oil line 4 and one of the control oil lines, such as the opening line 8, and the indicator device 6 is arranged in communication to the same control oil line, i.e. line 8.

The oil flow through the by-pass valve 5 may be regulated by means of arrangement of spring loaded non-return valve members in an operator valve arranged in connection with the actuator 1 and being connected to the control oil line 2 or 8, respectively, as well as the low pressure oil line 4, said operator valve comprising actuating means for said arrangement of non-return valve members operated by the position of the movable member of the actuator.

In Figure 3 an embodiment of such an operator valve is shown. It comprises a casing 11 having pipe line connections 12 and 13 for the control oil line 2 or 8 and the low pressure oil line 4, respectively. In the casing 11 an axial cylindrical bore 14 is formed, wherein there is arranged on one hand a tubular member 15 and, on the other hand, an end bushing 16. In the member 15 a working cylinder 17 is formed, the wall of which is provided with recesses 18 and 19 for a shoulder portion 20 on a valve bushing 21 and a pressure disk 22 for a load spring 23, only schematically shown, for a valve element 24 co-operating with a valve seat formed at the end opposite the shoulder portion 20 of the valve bushing 21 screwed into the interior portion of the member 15.

Outside the recess 18, the tubular member 15 forms together with the end bushing 16 a space 25 which communicates with the connection for the low pressure oil line through channels 26, which are formed in the member 15 opposite the shoulder portion 20 of the valve bushing 21.

At the end opposite the space 25, the working cylinder 17 communicates with the connection 12 for the control oil line through flow channels 27. In this end of the working cylinder, and in a narrowed extension 28 of the axial bore 14 behind the tubular member 15 there is furthermore arranged a flow control slide valve of a construction known per se with a slide member positioned in the working cylinder 17, in which a longitudinal channel 30 is formed which is connected through transverse channels 32 to the above mentioned connecting channels 27 for the connection 12 for the control oil line and communicates through a nozzle-like channel 33 having a small flow cross-sectional area with the interior of working cylinder 17.The position of the slide element 29 and thereby the regulation of the flow communication from the connection 12 for the control oil line to the working cylinder 7 depends in a known manner, on one hand, of the cross-sectional area of the nozzle-like channel 33 and, on the other hand, on the force from a load spring 34 arranged between two pressure disks 35 and 36, since oil is only allowed to flow through channel 33, when a difference pressure exists there across. Otherewise, this difference pressure acts on the end faces of the slide element 29. When the difference pressure has assumed a value which can overcome the spring force, the slide element will move in the direction of lower pressure and thereby reduce the flow cross-sectional area in the transverse channels 27 and 32 to a value corresponding to the spring pressure.Thus, the flow quantity is not dependent on the pressure in the working cylinder, but only on the difference pressure across the channel 33 and the cross-sectional area thereof. Since the difference pressure is very low, for example about 2 kp/cm2, the cross-sectional area of channel 33 may be relatively great. The slide element 29 will only block the flow when a flow is actually present. When no flow takes place, the slide element 29 returns to its intermediate position, as a result of which the system will have a tendency to sell-cleaning, if dirt should enter into the system.Furthermore, as a result of the low difference pressure across the channel 33, the flow velocity during the channel 33 will be almost independent of the fact, whether the flow direction is from the relatively high working pressure in the control oil line towards low pressure, or from low pressure to zero pressure in the control oil line.

In the end bushing 16 an axial bore 38 is provided, which towards the space 25 forms a recess 39 for a shoulder portion 40 on a spring-loaded pressure pin 41, a portion 42 of which projects outside the valve casing 11, between which shoulder portion 40 and the shoulder portion 20 of the valve bushing 21, a load spring 43 is arranged. On a narrowed portion 44 of the pressure pin 41, a valve element 45 is arranged, which is loaded by a spring 46 engaging the side or shoulder portion 40 facing the space 25. The valve element 45 serves to close the opening of the axial bore 47 in valve bushing 21 facing the space 25.

The spring-loaded valve element 24 forms together with the valve bushing 21 a first non-return valve, which is actuated towards its closed position by the load spring 23 as well as a possible oil pressure in the working cylinder 17.

An actuation and control portion 48 of the valve element 24 extends into the axial bore 47 of the valve bushing 21 and forms with one end an engagement for the pressure pin 41, so that the valve element by axial displacement of the pressure pin 41 towards the right in Figure 3 will be moved away from the closed position. The end 42 of the pressure pin 41 projecting outside the valve casing 11 engages a curve member 50, only schematically shown, which is coupled to the movable member of the actuator 1, so as to move synchronously with said member, and is formed with mutually off-set contact faces 51, 52 and 53 corresponding to fully open actuator, fully closed actuator and intermediate positions of the movable member of the actuator, respectively.Dependent on the construction of the movable member of the actuator 1, the curve member 50 may have the form of a rotatable ring or, as shown in Figure 3, a longitudinally displaceable oblong member.

In the position shown in Figure 3, the curve member 50 assumes a position corresponding to fully open actuator, which is to say that pressure oil has been supplied to the actuator 1 by means of the control valve 3 in Figure 1 or 10 in Figure 2, whereby the movable member of the actuator occupies one of its end positions. In this position of the curve member 50, the pressure pin 41, which is spring-biased in the direction towards the curve member, will be retracted from the end of the actuation and control portion 48 of the valve element 24, so that the valve formed by the valve element 24 together with the valve bushing 21 will be closed for oil passage from the working cylinder 17 to the space 25 and, as a result thereof, from the connection 12 to the connection 13.

If now the control valve 3 in Figure 1, or 10 in Figure 2 is switched to close the actuator 1, oil will start to flow from the actuator towards the return line. Thereby, the movable member of the actuator will start to move towards its other end position.

As a result thereof, the curve member 50 will be displaced downwardsly in Figure 3, so that the pressure pin by engagement of contact surface 53 with the projecting end 42 is forced a distance into the valve casing to engage the actuation and control portion 46 of the valve element 24. Thereby the valve element 24 will open without the valve element 45 closing the opposite opening of the axial bore 47 of the valve bushing 21 in this position of the pressure pin, so that it will be possible for oil to pass in a quite small quantity between the pipe line connections 12 and 13 of the operator valve for the control oil line and the low pressure oil line, respectively.

Thereafter, when the movable member of the actuator 1 assumes the end position corresponding to fully closed actuator, the curve member 50 will have been further displaced, so that now the contact face 52 will engage the projecting end 42 of the pressure pin 41, which will thereby displace the valve element 24 furtheron in the opening direction, but simultaneously allow closing of the opening of the axial bore 47 of the valve bushing 21 facing the space 25 by means of the spring-loaded valve element 45. In this situation, the oil pressure in the control oil line, and, thus, in the working cylinder 17 may have dropped to zero, whereas in the space 25, a relatively low oil pressure originating from the low pressure oil line will prevail.However, as a result of the closed valve at the valve element 45, no possibility will exist for oil passage from the space 25 to the working cylinder 17.

If, subsequently, the control valve 3 in Figure 1, or 10 in Figure 2 is switched again to the opening position, pressure oil will be supplied to the actuator 1, whereby the movable member thereof will start to move towards the end position corresponding to open actuator, so that the curve member 50 in Figure 3 will now be displaced upwardsly, whereby the projecting end 42 of the pressure pin 41 will leave the engagement with the contact face 52 and engage the contact face 53. By this movement the valve at the valve element 45 will be opened, but the valve element 24 will not yet close, so that as a result of the pressure in the control oil line, oil will now flow in a small quantity from the connection 12 through the working cylinder 17 to the space 25 and the connection 13.When the movable member of the actuator 1 has again assumed the end position corresponding to fully open actuator, the pressure pin 41 will again be removed from engagement with the actuation and control portion of valve element 24, whereby this valve member will close and block for oil passage from the connection 12 to the connection 13.

Thus, at fully open actuator, when working pressure prevails in the cylinder 17, the closed valve element 24 will block for oil passage, whereas at fully closed actuator, oil passage will be blocked by valve element 45.

If now the control valve 3 in Figure 1, or 10 in Figure 2 at fully closed actuator is switched to opening, whereby working pressure is established in the control oil line 2 in Figure 1, or the supply line 8 in Figure 2, but the force from the actuator 1 is insufficiently great to move the machine element, such as a valve, which is to be operated by the actuator, with the result that the movable member of the actuator remains in the end position corresponding to fully closed actuator, the curve member 50, which in this situation will be in engagement with the projecting end 42 of the pressure pin 41 with its contact face 52, will not be displaced upwardsly.However, as a result thereof, the valve element 24 will be in its open position, whereby the working pressure in the cylinder 17 will cause the otherwise closed valve at valve element 45 to open, so that a small oil quantity may pass from the working cylinder 17 to the space 25 and, thereby, from the connection 12 to the connection 13. Consequently, also in this situation with a blocked actuator, a small oil flow is obtained through the control oil line to act upon the indicator device 6.

On the contrary, if the control valve 3 in Figure 1, or 10 in Figure 2 is operated to close at fully open actuator, and the closing force from the actuator for some reason or another is insufficiently great to move the machine element to be operated by the actuator corresponding to the movable member of the actuator being maintained in the end position corresponding to fully opened actuator, in which the pressure pin 41 engages the end face 51 of curve member 50 and is removed from the actuation and control portion 48 of the valve element 24, so that the valve at valve element 45 is open, whereas the valve at valve element 24 is closed, a small quantity of oil will flow from the space 25, which communicates with the low pressure oil line to the working cylinder 17, since the pressure in space 25 will be sufficient to move the valve element 24 towards the open position, and the pressure in the working cylinder has dropped to zero, because the control oil line has been connected to the return line.

In this manner, an oil flow through the control oil line for operating the indicator device 6 in Figure 1 is obtained also in this other situation of a blocked actuator.

Finally, if the movable member of the actuator 1 during its movement from one end position to the other in order to open or close the actuator due to some hindrance or the other is stopped in an arbitrary position between the end positions, so that the flow of control oil to or from the actuator 1 itself ceases, a small oil flow through the operator valve will be obtained also in this situation as a result of the fact that both non-return valve members at valve elements 24 and 45 are open. If such a stop occurs during opening, the oil flow will be directed from the connection 12 for the control oil line to the connection 13 for the low pressure oil line, and if the stop occurs during closing, the oil flow will have the opposite direction.

Thus, it will appear that as long as the movable member of the actuator 1 is positioned between its end positions or in a situation, in which said member is blocked in one of the end positions, although it has been operated for movement towards the other end position, the adjustable by-pass valve according to the invention as realized for example by means of the operator valve in Figure 3 will effect an oil flow through the control oil line.The possibilities of producing this oil flow serving indicating purposes are not limited to the embodiment shown in Figure 3 of an operator valve mounted directly on the actuator, since, in principle, a possibility should only be present to operate the spring-loaded non-return valve arrangement incorporating valves at 24 and 45 in dependence of the actual position of the movable member of the actuator, which may also be obtained in another manner than by direct engagement, as shown in Figure 3. Furthermore, the non-return valve arrangement directly adjusting the by-pass valve need not be integrated with the flow control valve adjusting the oil quantity flowing through the by-pass valve.

The indicator device 6 in Figure 1 and 2, which shall be able to sense oil flowing through the control oil line both during adjusting movement of the movable member of the actuator 1 and in the above mentioned situations, in which said member for some reason or another has been blocked either in an end position or in an intermediate position between the two end positions, may be constituted by an indicator valve inserted in the control oil line 2 in Figure 1 or the suply line 1 in Figure 2 between the actuator 1 and the control valve 3 or 10, respectively, and incorporating a flow cylinder constituting a part of the control oil line, and a spring-loaded slide valve displaceably arranged therein which slide valve without any oil flow through the control oil line assumes a rest position and, in case of oil flow through the control oil line is moved in one or the other direction out of the rest position dependent on the flow direction.

In Figure 4 an embodiment of such an indicator valve is shown incorporating a casing 54, wherein a flow cylinder 55 is formed, said flow cylinder having at the ends two pipe line connections 56 and 57 for the control oil line 2 in Figure 1 or the supply line 8 in Figure 2. In the flow cylinder 55 there is arranged a spring-loaded, axially displaceable slide valve having a valve body 58 and a load-spring 59, schematically shown, which spring is positioned between two pressure rings 60 and 61 engaging an engagement ring 62 secured to the valve casing, and a shoulder portion 63 formed by valve body 58 together with an annular recess 64 at the wall of the flow cylinder 55, respectively.In the upwards direction in Figure 4, oil flow through the indicator valve from the connection 57 takes place through channels 65 in the lower part of valve body 58 towards a space 66 formed by depressions in the wall of flow cylinder 55 and valve body 58, respectively, which space in the position shown in Figure 4 is closed upwardsly by engagement faces on opposite annular projections 67 amd 68 from the wall of flow cylinder 55 and valve body 58, respectively, contacting each other.Above said projections, a space 69 is formed by despressions in the wall of the flow cylinder and the valve body, respectively, which space through channels 70 parallel to the axis and formed in a projection from the wall of the flow cylinder forming the above mentioned annular engagement face 64 for the pressure disc 61 of the load-spring 59, communicates with a space 71 around the load spring 59, which space is connected through channel 72 between the valve casing and the engagement ring 62 for the other pressure disc 60 of the load spring 59 to the pipe line connection 56.In an axial bore 73 formed in valve body 58 and communicating downwardsly through channel 74 with the flow space 66 around the lower part of the valve body, while being closed upwardsly by a stopper 75 and a stop pin 76, the ends of which form engagements for the pressure disc 60 of load spring 59, there is inserted a flow control valve of the same construction as the flow control valve between the working cylinder 17 and the control oil line connection 12 in the operator valve in Figure 3. In the flow control valve in Figure 4, the longitudinal channel 78 of valve body 77 communicates through a nozzle-like channel 79 with the lower part of the cylindrical bore 73 and through transverse channels 80 and corresponding transverse channels 81 in the valve body 58 with the above mentioned space 69 between the valve body 58 and the wall of the flow cylinder 55.

If there is no oil flow through the control oil line and thereby through the flow cylinder 55, the valve body 58 will assume the rest position shown in Figure 4, in which the contact between the engagement faces on projections 67 and 68 will block for oil flow between the spaces 66 and 69 around the valve body 58. This situation occurs both after finished adjustment of the actuator when full working pressure prevails in the control oil line and when there is no oil pressure in this line.On the contrary, if oil flows in one direction or the other through the control oil line, the valve body 58 will be moved against the action of load spring 59 in one or the other direction out of the rest position shown in Figure 4 and thereby open for passage of oil between the above mentioned spaces 66 and 69 around the valve body, so that a free flow passage through the cylinder 55 is established through channels 65, space 66, space 69, channels 70, space 71 and channels 72. As soon as the flow ceases again, the valve body 58 will return to the rest position shown in Figure 4 due to the action of load spring 59.The flow control valve 77 has the effect that even in the rest position shown in Figure 4, in which oil passage between the spaces 66 and 69 is blocked, a small quantity of oil can pass through the indicator valve without the valve body 58 being moved out of the rest position.

However, the flow cross-sectional area of channel 79 is smaller than the flow crosssectional area of the corresponding nozzlelike channel 33 in the flow control valve in the operator valve in Figure 3. Thereby, an oil quantity which may pass through channel 33 will not be able to pass channel 79, but cause the valve body 58 to be moved out of its balanced position. In this manner, the flow control valve of the indicator valve establishes a threshold for the indicator function.

However, it can be replaced by a throttle screw in a by-pass bore between bores 56 and 57, since between these bores the maximum difference pressure would be determined by the force from load spring 59. The flow control valve may also be replaced by a suitable clearance between the valve body 58 and the casing 54. It is only important that the oil which may pass through channel 33 cannot pass between bores 56 and 57 without moving valve body 58 out of its balanced position.

In principle, the movement of the valve body 58 of the indicator valve out of the rest position shown in Figure 4 may be utilized for a direct visual indication by connecting the valve body 58 in a manner not further illustrated to indicator means positioned outside valve casing 54 and moving in syncronism with valve body 58 relative to an indicator scale, on which the rest position is marked. When the actuator 1 in Figure 1 or 2 is either open or closed, and full working pressure or no pressure, respectively, prevails in the control oil line, the indicator means will be positioned opposite the rest position mark.As soon as an oil flow arises through the by-pass valve formed by the operator valve in Figure 3, and as a result thereof through the control oil line due to adjustment of the actuator or blocking of the movable memeber thereof, the indicator means would, however, be moved away from the rest position mark, whereby a direct visual control of the function of the actuator is obtained.

However, in a preferred embodiment the movement of the valve body 58 out of the rest position is utilized to obtain an electrical indication in that in the indicator valve in co-operation with the valve body, an operating member for an electric indicator device is arranged to be influenced by the movement of the valve body in one or the other direction out of the rest position. As more clearly illustrated in the cross-sectional view in Figure 5, this operating member is constituted in the embodiment shown of the indicator valve by a spindle 83 rotatably arranged in a bore 82 extending transverse to the flow cylinder 55, said spindle having an actuating arm 84 engaging the valve body 58 so as to turn the spindle 83 by movement of the valve body in one or the other direction out of the rest position.This rotational movement of the spindle 83 in one or the other direction is utilized by a switch actuating means 85 secured to the spindle to actuate switches in an electric indicator circuit, not further illustrated, so as to obtain in this manner an indication of movement of the valve body 58 out of the rest position in Figure 4.

As further illustrated in Figure 5, the spindle 83 is furthermore arranged to be axially displaceable in the bore 82 against a spring load. The bore 82 forms a chamber communicating with the space 66 of the flow cylinder 55, so that a part 86 of enlarged cross-section and positioned in this chamber at full oil pressure in the flow cylinder will be influenced by said oil pressure acting on the end face of said part 86 shown to the left in the figure to axially displace the spindle 83 against the action of a load spring 89 arranged between two pressure discs 87 and 88 towards a position, in which the switch actuation means 85 operates a further switch 90 incorporated in the electric indicator circuit.On the contrary, in the absence of oil pressure in the flow cylinder 55, the spindle 83 will assume the position shown in Figure 5, in which the last mentioned switch 90 is deactuated due to the action of load spring 89.

As an example, the construction of the electric indicator circuit not shown, which is operated by the spindle 83 through switch actuating means 85 may be such that the switches actuated by rotation of the spindle 83 starts a flash relay connected to a lamp and simultaneously turns the above mentioned further switch off, so that in case of no oil pressure in the control oil line and the valve body of the indicator valve assuming the rest position shown in Figure 4, the lamp will be extinguished, whereas in the other stationary condition of the valve body of the indicator valve with open actuator and full working pressure in the control oil line, the lamp will light constantly. When the spindle 83 is turned in one or the other direction by oil flow through the indicator valve, the lamp will flash, so that an unambiguous electric indication is obtained of the actuator being open or closed or operated to perform an adjusting movement. Through the duration of the period, in which the lamp flashes, an indication is furthermore obtained of the fact whether the actuator is operating correctly, or the movable member thereof is possibly blocked.

Figures 6 and 7 shows a modification of the indicator device in case of use of an indicator according to the invention in connection with an actuator of the kind which is opened against a variable closing force, so that the necessary opening pressure depends on the actual position of the movable member of the actuator and, as a result thereof, proportionality exists between the pressure in the control oil line and said actual position. The figures show only the part of the system, which is constructed in a manner different from that shown in Figure 1. Thus, the control oil line 2 and the low pressure oil line 4 are connected in the same manner as in Figure 1 to an actuator 1 and an adjustable by-pass valve 5, which can be established by means of an operator valve, as shown in Figure 3.In Figure 6 the working pressure line and the return line are intended to be connected to a motor pump system, and as shown symbolically, a control valve 98 which in addition to an opening position and a closing position which are indicated by the same symbols as used in Figure 2 has a neutral position, in which the control oil line 2 is connected to the return line through a pilot controlled counter valve 99.

Correspondingly, in Figure 7 the working pressure line is connected to a manual pump unit 100 having such a capacity adjusted to the flow cross-sectional area in the operator valve in Figure 3 that an oil flow in the control oil line by-passing the actuator through the operator valve constitutes only a small fraction of the pump capacity. In connection therewith, the control valve 101 in this embodiment is constructed so as to close in a drop-tight manner to prevent the passage of oil through control oil line 2.

Both in Figures 6 and 7, the indicator means is constituted in a simple manner by a manometer 102 having a scale with marks for fully opened and fully closed actuator, said manometer replacing the indicator valve in the embodiments shown in Figures 1 and 2.

As mentioned in the foregoing, in systems of the kind referred to it is possible to adjust the actuator to intermediate positions, i.e.

to secure the movable member of the actuator in positions between the two end positions corresponding to fully opened and fully closed actuator. In connection therewith it will often be acceptable to limit the number of such possible intermediate positions to a determined number of fixed positions corresponding for example to 10% open, 25% open, 50% open etc. between the end positions corresponding to full closing or full opening.

In such a case, a position indicator according to the invention having an indicator means in the form for example of a manometer may in a simple manner be modified to provide an indication also for the movable member of the actuator assuming one of said discrete intermediate positions. For this purpose, the curve member coupled to the movable member of the actuator and serving to operate the operator valve in Figure 3 may, as shown in Figure 8 in which said curve member is designated by 103, be formed with a number of cut-outs each corresponding to one of said intermediate positions, so that the pressure pin 41 of the operator valve, which is illustrated in Figure 1 by its outer contour, only by engagement between the projecting end 42 and one of said depressions 104, is removed from acting upon the actuation and control portion 48 of the valve member 24, so as to bring the counter valve arrangement in the same condition as in case of fully opened actuator.

By opening of the actuator in a system as shown in Figure 6, the control valve 98 is 'switched to the opening position, which is marked by the extreme left symbol, whereby oil flows through the control valve 98 and the pilot controlled counter valve 99 to the control oil line 2 and therefrom to the actuator 1. During the opening movement, a small flow of oil will take place through the by-pass valve to the low pressure oil line apart from the above mentioned discrete intermediate positions.

Whenn the actuator is fully open, the counter valve 99 closes, and the control valve 98 is adjusted to the neutral position shown in the figure, whereby the actuator will be maintained in the fully open position, which can be read on the manometer 102.

When the actuator is closed, the control valve 98 is brought to the closing position shown by the extreme right symbol in Figure 6, whereby the pilot controlled counter valve will be opened for return of oil to the return line. Simultaneously, the pressure indicated on monometer 102 drops to zero, which can be read on the manometer 102, and when the actuator has been closed, the control valve 98 is switched again to the neutral position. The manometer should now provide a zero indication. However, if the suspicion arises that the actuator is not fully closed, but is blocked in some intermediate position or another, the control valve 98 is readjusted for a short time in the opening position after which it is adjusted to the neutral position again.Thereby the actuator will open a bit relative to the assumed position and thereafter close slowly again, whereby oil flows from the control oil line to the low pressure line 4. The pressure indicated on the manometer is reviewed. If the pressure suddenly drops to zero from a value above the minimum pressure neces sary to start the opening movement, the only reason would be that the actuator is prevented from closing by mechanical reasons. If the pressure suddenly drops to zero from a value corresponding to the minimum pressure, one will know that the actuator has been fully closed.

If the actuator is to be adjusted to one of the discrete intermediate positions, as shown in Figure 8, the control valve 98 is operated to open until the movable member of the actuator during the opening movement has passed the intermediate position desired. Thereafter, the control valve 98 is switched to the neutral position, whereby the actuator closes slowly until the projecting end 42 of the pressure pin of the operator valve engages the nearest cutout 104 in the curve member 103, by which engagement the movable member of the actuator will now be secured in the corresponding intermediate position. It is read on the manometer, whether the desired intermediate position has been occupied.If further closing is necessary, the control valve 98 is adjusted shortly to the closing position and thereafter readjusted to the neutral position, whereby the movable member of the actuator will again move slowly in the closing direction, until the projecting end of the pressure pin engages the following cut-out 104 in the curve member ]03.

If it appears during opening of the actuator that the movable member has been blocked, the control valve 98 is adjusted to the neutral position, whereby the pressure will quickly drop to zero since oil flows through the counter valve 99 back to the return line, whereby an indication is obtained of an incorrect opening function of the actuator.

In the embodiment shown in Figure 7, the procedure is substantially the same, since as mentioned only a manual pump unit 100 is used instead of the motor pump system, and the control valve 98 and the counter valve 99 in Figure 6 have been replaced by a droptight blocking valve. The operating procedure of opening and closing of the actuator and adjustment to one of the intermediate positions as well as the registration by means of the manometer 102 takes place essentially in the same manner as explained above.

Even if the construction shown in Figure 8 of the curve member coupled to the movable member of the actuator is particularly suitable for use in connection with the above mentioned actuators of the kind, in which the opening takes place against a variable closing force and, by use of said curve member, a positive feed back information can be obtained of the fact, whether the movable member of the actuator has occupied discrete intermediate positions such a curve member provided with cut-outs may also be used in connecton with an actuator of the kind described with reference to Figures 1 and 2, in which no proportionality exists between the pressure in the control oil line and the position of the movable member of the actuator.Also in case of such an actuator, the particular advantage is obtained thereby that the movable member can be adjusted to assume a number of discrete intermediate positions between the end positions corresponding to fully open or fully closed actuator, since the movable member of the actuator can be secured in such intermediate positions as a result of the engagement between the curve member formed with cut-outs and the projecting end 42 of the spring-loaded pressure pin of the reporting valve. In this particular case there will not be obtained any unambiguous feedback information on the movable member of the actuator being secured in an intermediate position, but in many cases this would not be necessary either, since a skilled operator would be able to decide without difficulty during the operation which position the actuator is occupying.

In case of such an actuator, the occupation of an intermediate position may take place in that by means of the control valve there is the actuator is caused to open beyond the intermediate position desired to be occupied, whereafter the control valve is adjusted to a neutral position. The actuator will now close quite slowly to the nearest intermediate position. If further closing of the actuator is desired, the control valve is adjusted shortly to th closing position and thereafter readjusted to the neutral position. The actuator will now again close quite slowly to the next intermediate position etc.

This procedure is continued until the desired intermediate position has been occupied.

By use of the indicator device according to the invention with actuators of the kind, the opening of which takes place against a variable closing force, and in which feedback information may be obtained of the movable member of the actuator occupying a number of intermediate positions, as explained with reference to Figures 6 and 7, there may be used as indicator means instead of the manometer 102 shown in Figures 6 and 7 an electric indicator device in connection with an indicator valve of the same principal construction as shown in Figure 4.

Figure 9 shows an embodiment of such an indicator valve, which in this case is directly coupled with a control valve formed as a control cock and corresponding to the control valves 3 and 10, respectively, in Figures 1 and 2. This control cock which is instal lated in a control panel has an operating handle 105, which can turn a spindle 110 journalled rotatable in a cock casing 106 and being influenced by a disc spring 107 through a disc raise 108 and a needle rim 109, said spindle being firmly secured with a distributor casing 111, the end face of which .engages a distributor disc 112 in an oil-tight but turn able manner, which distributor disc is connected firmly with a manifold 113, which is screwed in an oil-tight manner onto the end of cock casing 106 opposite the operating handle 105.The manifold 113 has on one hand a pipe line connection 114 for the control line leading to the actuator in question corresponding to the control line 2 in Figue 1 and, on the other hand, through bores 115 and 116 for the supply of oil under working pressure and the return of oil to tank through pipe lines which may be common to a number of control cocks of the construction shown.

In the figure, the control cock is shown in a neutral position. By turning to one or the other side out of this position, the working pressure line 115 or the return line 116, respectively, may be connected to a cham ber 117 extending through the distributed disc 112 and some distance into the distribu tor casing 111. In the same manner as the indicator valve shown in Figue 4, the distri butor casing 111 has a flow cylinder 118, in which a spring-loaded slide valve 119 is arranged of the same principal construction as the slide valve 58 in Figue 4 and formed in the same manner with an axial bore, in which a spring-loaded flow control valve 120 of the same principle construction as the flow control valve 77 in Figure 4 is arranged.

Therefore, in the same manner as in the embodiment in Figure 4, the slide valve 119 will in this case, when there is rio oil flow from the working pessure line 115 to the connection 114, or from this connection to the return line 116 assume the rest position shown in the figure, in which the passage of oil is closed between a space connectd with a flow cylinder 118 and communicating through transverse channels 122 with the flow control valve 120 and between a space 123 in the spindle 110, from whch a com munication extends through transverse channels 124 to a space 125 outside the distributor casing 111 and communicating with the pipe line connection 114.In this position of the slide valve 119, a possibility exists only for a small oil quantity to pass from the channel 117 to the space 125 through the flow control valve 120 posi tioned in slide valve 119 in the same manner as in the embodiment in Figure 4.

In the embodiment shown, an indicator piston 126 is secured to the end of slide valve 119 facing the operating handle 105, the opposite end of which piston is formed with a groove 127, which in the rest position shown in the figure is in engagement with a switch actuating rod 128 for an electric switch 129. In view of balancing the slide valve 119 against oil pressures at the two ends of the slide valve, an extension plunger 130 is furthermore secured to the opposite end of the slide valve 119 remote from the operating handle 105. When the working pressure line 115 by turning of the operating handle 105 has been connected to the channel 117, the slide valve 119 will be moved out of the rest position shown in the figure in the direction towards the operating handle 105, whereby the indicator piston 126 will actuate the electric switch 129 through the switch actuating rod 128.On the contrary, if the return line 116 has been connected to the channel 117, the slide valve 119 will move in the direction away from the operating handle 105, whereby the indicator piston 126 will likewise actuate the switch 129 through the switch actuating rod 128. In the same manner as explained in the foregoing, the switch actuation may be used to start a flash relay so that a lamp is caused to flash as an indication of the slide valve 119 being moved out of its rest position as a result of oil flowing through the indicator valve.

In view of the fact that the embodiment shown of the indicator valve as mentioned in the foregoing is particularly intended to give electrical feedback information on the occupation of the movable member of the actuator of one of a number of discrete intermediate positions in addition to the end positions corresponding to fully closed and fully open actuator, there is additionally associated a number of position indicator lamps 143 to the indicator valve corresponding to the number of positions which the movable member of the actuator should be able to occupy, these lamps being actuated through a corresponding number of oil pressure switches coupled to the indicator valve, only one of which is shown in the figure.This oil pressure switch comprises a switch actuating pin 132 movably arranged in a cylinder 131, which pin may actuate an electrical switch 133 with one end and is influenced in its other end by pressure from a load spring 135 through a piston 134, the spring pressure of this spring being adjustable by means of, for example, a screw 136.

For oil-sealing purposes two O-rings 137 and 138 are arranged around the shaft of the contact actuating pin 132, th first of said rings being positioned stationarily between two securing rings 139 and 140 surrounding the contact actuating pin 132 with a reasonable clearance, whereas the other O-ring 138 engages the head of the switch actuating pin 132 influenced by piston 134.

The space around the contact actuating pin 132 betwen the two O-rings 137 and 138 communicates through a transverse channel 141 in the cylinder 131 and a channel 142 in the cock casing 106 with the space 125 around the distributor casing 111, so that in this space between the two O-rings the same oil pressure will prevail as in the space 125.

By suitable adjustment of the pressure from load spring 135 the contact actuating pin may be caused to actuate the contact 133 at a given value of the oil pressure between the two O-rings 137 and 138 and, thus, for a given position of the movable member of the actuator, since, as mentioned in the foregoing, proportionality exists between the position of the movable member of the actuator and the oil pressure in the control oil line in case of actuators of the kind referred to, which are opened against a variable closing force.

In this matter, electrical feedback information is obtained about the movable member of the actuator occupying a number of discrete intermediate positions corresponding, for example, to 50% open, 25% open and 10% open.

When the control cock with a built-in indicator valve shown in Figure 9 is used for actuators which shall only be either fully open or fully closed, only one oil pressure switch is coupled with the indicator valve.

The embodiment shown in Figure 9, in which the indicator valve is integrated in the control valve and, therefore, intended for direct installation in a control panel is particularly suitable for actuators which should only be operable from a single operation or control panel. In a different manner, the embodiment of the indicator valve shown in Figures 4 and 5 may be mounted any arbitrary place in the control oil line between the control panel and the actuator and is, therefore, suitable for application together with actuators which shall be operable from a number of operation and control panels at different locations.

WHAT I CLAIM IS: 1. A device for indicating the working state of a hydraulic actuator of the kind having a movable member movable between a closed position and an open position under pressure of oil supplied through at least one control oil line and with which there is also associated a low pressure oil line, characterised in that there is provided between the control oil line or one of the control oil lines and the low pressure oil line a controllable by-pass valve which is controlled in dependence on the position of the movable member of the actuator in such a manner that passage of oil through the by-pass valve is prevented when the movable member is in the fully open position with working pressure in said control oil line or in the fully closed position with no pressure in said control oil line, whereas oil is allowed to flow through the by-pass valve at a low flow rate, substantially independent of the direction of flow of oil between said control oil line and the low pressure oil line, when the movable member is in any position other than the fully open or fully closed position or when the movable member is in the fully open position with no pressure in said control oil line or in the fully closed position with working pressure in said control oil line, the said oil flow operating an indicator device arranged in communication with said control oil line at a location remote from the actuator.

2. A device as claimed in Claim 1, characterized in that said by-pass valve is regulated by an arrangement of springloaded non return valve members in an operator valve mounted on the actuator casing and connected with said control oil line as well as the low pressure oil line, said operator valve comprising actuating means for said non-return valve members controlled by the position of the movable member of the actuator.

3. A device as claimed in Claim 2, characterized in that said non-return valve members comprise a first non-return valve which is inserted in one end of a working cylinder which communicates in its other end with the said control oil line through a communication adjusted by means of a flow control member and having a small flow cross-sectional area, so as to cause said first non-return valve to be closed for flow of oil in said control oil line, whereas said first non-return valve is displaceable away from its closed position by said actuating means, as well as a second non-return valve having a spring-loaded valve member which is displaceably mounted on said actuating means so as to be able to close for flow of low pressure oil from a space outside said working cylinder through said first nonreturn valve into the working cylinder and therefrom into the said control oil line in the fully closed position only of the actuator.

4. A device as claimed in Claim 3, characterized in that said actuating means comprises a spring loaded pressure pin which is displaceably mounted in the operator valve and projects with one end out of said valve to engage a curve member connected with the movable member of the actuator and having mutually offset contacting faces for said one end of the pressure pin corresponding to fully open and fully closed actuator and intermediate positions of the movable member of the actuator.

5. A device as claimed in Claim 4, characterized in that said curve member is formed with a number of cut-outs to engage said one end of the pressure pin at fully open actuator and in a number of discrete

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. pin 132 betwen the two O-rings 137 and 138 communicates through a transverse channel 141 in the cylinder 131 and a channel 142 in the cock casing 106 with the space 125 around the distributor casing 111, so that in this space between the two O-rings the same oil pressure will prevail as in the space 125. By suitable adjustment of the pressure from load spring 135 the contact actuating pin may be caused to actuate the contact 133 at a given value of the oil pressure between the two O-rings 137 and 138 and, thus, for a given position of the movable member of the actuator, since, as mentioned in the foregoing, proportionality exists between the position of the movable member of the actuator and the oil pressure in the control oil line in case of actuators of the kind referred to, which are opened against a variable closing force. In this matter, electrical feedback information is obtained about the movable member of the actuator occupying a number of discrete intermediate positions corresponding, for example, to 50% open, 25% open and 10% open. When the control cock with a built-in indicator valve shown in Figure 9 is used for actuators which shall only be either fully open or fully closed, only one oil pressure switch is coupled with the indicator valve. The embodiment shown in Figure 9, in which the indicator valve is integrated in the control valve and, therefore, intended for direct installation in a control panel is particularly suitable for actuators which should only be operable from a single operation or control panel. In a different manner, the embodiment of the indicator valve shown in Figures 4 and 5 may be mounted any arbitrary place in the control oil line between the control panel and the actuator and is, therefore, suitable for application together with actuators which shall be operable from a number of operation and control panels at different locations. WHAT I CLAIM IS:

1. A device for indicating the working state of a hydraulic actuator of the kind having a movable member movable between a closed position and an open position under pressure of oil supplied through at least one control oil line and with which there is also associated a low pressure oil line, characterised in that there is provided between the control oil line or one of the control oil lines and the low pressure oil line a controllable by-pass valve which is controlled in dependence on the position of the movable member of the actuator in such a manner that passage of oil through the by-pass valve is prevented when the movable member is in the fully open position with working pressure in said control oil line or in the fully closed position with no pressure in said control oil line, whereas oil is allowed to flow through the by-pass valve at a low flow rate, substantially independent of the direction of flow of oil between said control oil line and the low pressure oil line, when the movable member is in any position other than the fully open or fully closed position or when the movable member is in the fully open position with no pressure in said control oil line or in the fully closed position with working pressure in said control oil line, the said oil flow operating an indicator device arranged in communication with said control oil line at a location remote from the actuator.

intermediate positions of the movable member of the actuator between' the end positions corresponding to fully open and fully closed actuator.

6. A device as claimed in any of the preceding claims, characterized in that said indicator device is constituted by an indicator valve arranged in said control oil line between the actuator and a control valve for switching the actuator between closing and opening, said indicator valve comprising a flow cylinder constituting a portion of said control oil line and a spring-loaded slide valve displaceably arranged in said cylinder and assuming a rest position in case of no oil flow through said control oil line, said slide valve being movable, by oil flow in said control oil line, out of said rest position in one direction or the other dependent on the flow direction.

7. A device as claimed in Claim 6, characterized in that a communication adjustable by a flow control member and having a small flow cross-sectional area is formed in said slide valve to allow passage of a small amount of oil without any movement of the slide valve.

8. A device as claimed in Claims 3 and 7, characterized in that the flow crosssectional area of the communication in said indicator valve is smaller than the flow cross-sectional area of the communication between the working cylinder of said operator valve and said control oil line:

9. A device as claimed in any of Claims 6, 7 or 8, characterized in that said slide valve is extended outside said indicator valve to directly visually indicate whether it assumes its rest position or has been moved away therefrom in one direction or the other.

10. A device as claimed in any of Claims 6, 7 or 8, characterized in that an operating member for electrical indicating means to indicate that the slide valve does not assume its rest position is mounted in said indicator valve in communication with said slide valve to be activated by the movement of said slide valve in one or the other direction out of said rest position.

11. A device as indicated in Claim 10, characterized in that said operating member is constituted by a spindle mounted rotatably in a bore extending transverse to the flow cylinder of the indicator valve and having an actuating arm engaging said slide valve to rotate the spindle by movement of the slide valve in one or the other direction out of said rest position.

12. A device as claimed in Claim 11, characterized in that said spindle is additionally mounted in its bore to be axially displaceable under spring-bias and has one end positioned in a space connected with said flow cylinder, so that the spindle is displaced towards a first position in case of oil pressure in said control oil line and assumes a second position in case of no oil pressure in said control oil line, said spindle operating said electrical indicating means to indicate open or closed actuator in said first and second positions, respectively.

13. A device as claimed in any of Claims 1 to 5 of the kind, in which said actuator is opened against a variable closing force, characterized in that said indicator device is constituted by a manometer arranged in communication with said control oil line.

14. A device as claimed in Claim 10, characterized in that said operating member is constituted by an indicator piston secured to one end of said slide valve and being axially displaceable by the movement of said slide valve in one or the other direction out of said rest position for operating a switch actuating rod.

15. A device as claimed in Claim 5 of the kind, in which the actuator is opened against a variable closing force, characterized in that a number of oil pressure switches corresponding to the number of intermediate positions in addition to one end position of the movable member of the actuator are coupled with said indicator valve, each of said oil pressure switches comprising a switch actuating pin influenced by a spring having an adjustable spring pressure and being arrangd in a cylinder, an oil-tightly sealed portion of which communicates with a portion of the flow cylinder of the indicator valve so as to actuate said switch actuating pin against said adjustable spring pressure by the oil pressure present in said flow cylinder, the spring pressure of each oil pressure switch being adjusted to cause the switch actuating pin to actuate an electrical switch at an oil pressure corresponding to a given position of the movable member of the actuator.

16. A device for indicating the working state of a hydraulic actuator, substantially as described hereinbefore with reference to the accompanying drawings.