DE20305232U1 - Valve block has HP and LP valves both connected on outlet side to common working channel and each with switchable valve component by which connection between respective valve inlets and outlets is selectively closed or opened - Google Patents

Abstract

The valve block has an inlet side high-pressure valve connected to a HP feed passage, and an inlet side low-pressure valve connected to a LP feed passage. Both valves on the outlet side are connected to a common working channel and each have a switchable valve component by which the connection between the respective corresponding valve inlet and valve outlet is selectively shut off or opened. The connection between the outlet of the LP valve and working channel is check valve free.

Description

G 22398 - les 3 March 2003

FESTO AG & Co, 73734 Esslingen Valve block

The invention relates to a valve block which is used in particular for controlling the compressed air in the blow molding of plastic bottles.

When blow molding plastic bottles, a hollow molded part is usually produced using an extruder, which is then blown up in a mold so that the plastic material forming the bottle wall adheres to the inner surface of the correspondingly contoured mold, while maintaining the desired wall thickness. So-called PET bottles in particular can be produced in this way.

In order to achieve an exact shape of the bottle wall, the hollow body molding is pressed against the mold wall at a high pressure of around 25 to 40 bar. In order to prevent the plastic material from tearing, however, the high pressure is preceded by a low pressure application, in which the hollow body molding is pre-blown at a low pressure of around 16 bar.

One problem with the corresponding compressed air control is that when switching from low pressure to high pressure, a pressure drop occurs in the working channel that is connected to the low pressure valve and the high pressure valve and leads to the mold, which at the same time results in an extension of the processing time required to mold a plastic bottle. It could be considered to provide a check valve in the connection between the valve outlet of the low pressure valve and the working channel, which prevents the high pressure fluid from flowing back into the low pressure valve if the high pressure valve is switched over too early. However, due to the high pressure level, a considerable amount of effort would be required to implement a suitable check valve.

It is the object of the present invention to provide a valve block which enables a rapid transition from the low-pressure phase to the high-pressure phase with a cost-effective construction in the working channel.

This task is solved by a valve block, in particular for compressed air control in the blow molding of plastic bottles, with a high-pressure valve connected to a high-pressure feed channel on the inlet side and a low-pressure valve connected to a low-pressure feed channel on the inlet side, which two valves are connected to

are connected to a common working channel and each have a switchable valve member with which the connection between the respectively assigned valve inlet and valve outlet can be optionally blocked (closed position) or released (open position), wherein the connection between the valve outlet of the low-pressure valve and the working channel is designed without a check valve and wherein the valve member of the low-pressure valve is designed with regard to its active surfaces oriented in the switching direction and exposed in the open position to the fluid pressures present via the valve inlet and the valve outlet in such a way that these fluid pressures in the open position produce a resulting actuating force on the valve member in the closing direction.

In this way, switching the high-pressure valve to the open position does not require waiting until the low-pressure valve has switched to the closed position. The corresponding switching process of the high-pressure valve can be initiated at the same time or even shortly before the switching process of the low-pressure valve. Thus, switching from low pressure to high pressure is not accompanied by a significant drop in pressure in the working channel, which enables the desired compressed air application process, especially when blow molding a plastic bottle, to be carried out in a shorter time. By dispensing with a check valve between the valve outlet of the low-pressure valve and the working channel, the aforementioned advantage is achieved with a cost-effective design.

—&Lgr;

It is true that, due to the absence of the check valve, the activated high pressure can also enter the low-pressure valve via the common working channel when the switching processes overlap. However, due to the special design of the active surfaces of the valve element of the low-pressure valve, this pressure build-up does not impair the closing process of the low-pressure valve, but rather supports it with an additional fluid closing force, so that the closing of the low-pressure valve takes place very quickly.

Advantageous further developments of the invention emerge from the subclaims.

Preferably, there is at least one first active surface responsible for generating an actuating force in the closing direction and at least one second active surface responsible for generating an actuating force in the opening direction on the valve member of the low-pressure valve, wherein the first active surfaces are larger than the second active surfaces.

A further reduction in the switching time is achieved if the low-pressure valve and the high-pressure valve are each assigned an electrically activated pilot valve for actuation. These pilot valves are preferably connected to a common pilot channel.

The valve block is also expediently equipped with at least one vent valve, which is connected to the working channel on the inlet side and leads to the atmosphere on the outlet side. The working channel can be quickly vented via this at least one vent valve, for example after completion of a blow molding process. By using several vent valves connected in parallel, the venting process can be carried out particularly easily and in a timely manner.

The vent valve is also conveniently operated using an electrically operated pilot valve. The latter is conveniently connected to the same pilot channel as the pilot valves of the low-pressure valve and the high-pressure valve, if present.

It is particularly advantageous to use a vent valve of the "Normally Closed" type, while the associated pilot valve is of the "Normally Open" type. A check valve that opens in the direction of the pilot valve and a pressure accumulator between this check valve and the pilot valve are conveniently installed in the pilot channel leading to the pilot valve. In this way, the working channel can be vented via the compressed air volume accumulating in the pressure accumulator even if

still possible if a power failure or a failure of the air supply occurs due to a malfunction.

During operation, the low-pressure valve is conveniently operated with a low pressure of up to a maximum of 16 bar. The high-pressure valve is conveniently operated with a high pressure of up to 40 bar.

A particularly compact design is achieved when the high-pressure valve, the low-pressure valve and, if present, at least one vent valve have a common valve housing that accommodates the functional components.

The invention is explained in more detail below with reference to the accompanying drawings, in which:

Fig. 1 shows a preferred design of the valve block according to the invention in perspective view,

Fig. 2 is a longitudinal section through the valve block from Fig. 1, but without showing the actuating element of an optionally provided throttle device,

Fig. 3 the circuit diagram of the valve block according to Fig. 1 and 2 and

_7_

Fig. 4 shows a partially broken section of a variant of the valve block in the area of the low-pressure valve, whereby in particular a modified design of the valve member can be seen.

The drawing shows a compact valve block, designated as a whole by reference number 1, in which a low-pressure valve 2, a high-pressure valve 3 and a vent valve 4 are combined.

The above-mentioned three valves 2, 3, 4 expediently have a common valve housing 5. In this valve housing 5, an elongated valve chamber 6a, 6b, 6c is formed for each valve 2, 3, 4, whereby these valve chambers 6a, 6b, 6c are arranged in parallel alignment at the same axial height in a row. The direction of the arrangement is indicated by dash-dotted lines at 7.

The three valves 2, 3, 4 mentioned are designed as 2/2-way valves in the embodiment. Their valve chambers 6a, 6b, 6c are each divided by an overflow opening 8 into an inlet valve chamber 12a, 12b, 12c and an outlet valve chamber 13a, 13b, 13c. In each valve chamber 6a, 6b, 6c there extends an elongated valve member 14a, 14b, 14c which passes through the associated overflow opening 8 and is provided with a preferably plate-shaped closure section which surrounds the overflow opening 8.

&bgr;• ·

the axially oriented, housing-fixed valve seat 16 is axially opposite.

The inlet valve chamber 12a of the low-pressure valve 2 is connected to a low-pressure feed channel 17, which is fed with a fluid pressure Pl referred to as "low pressure" when the valve block 1 is in operation. For this purpose, the valve housing 5 contains an interface 18a to which a fluid line coming from the corresponding pressure source can be connected. In a typical application, in connection with the blow molding of plastic bottles, the low pressure Pl provided amounts to up to 16 bar. By means of a throttle device 22 connected in the course of the low-pressure feed channel 17, which can be variably adjusted via an actuating element 23 accessible from the outside, the flow on the inlet side of the low-pressure valve 2 can be varied as required.

The inlet valve chamber 12b of the high-pressure valve 3 is connected to a high-pressure feed channel 24 which in turn passes through the valve housing 2 and leads to a further interface 18b via which a fluid pressure P2 referred to as "high pressure" can be supplied. In the application mentioned, the high pressure P2 provided is approximately 25 to 40 bar. It is in any case higher than the low pressure Pl.

The outlet valve chambers 13a, 13b of the low-pressure valve 2 and the high-pressure valve 3 are connected to a common working channel 25 which passes through the valve housing 5 and leads to at least one third interface 18c to which a fluid line leading to the device to be controlled can be connected. This fluid line leads, for example, to a blow head of a device used to produce plastic bottles or other plastic containers.

In the exemplary embodiment, the working channel 25 has at least one further interface 18d, which can be used alternatively or additionally. In the exemplary embodiment, it is not used and is therefore tightly closed by means of a closure plug 26.

The vent valve 4 is connected with its inlet valve chamber 12c to the common working channel 25. Its outlet valve chamber 13c is connected to the atmosphere via a vent channel 27 that opens out onto the outer surface of the valve housing 5. It is possible to equip the vent channel 27 with an interface that allows the connection of a silencer or a ducted discharge of the exhaust air.

The three valves 3, 4, 5 are each of the "Normally Closed" type. Each valve member 14a, 14b, 14c is constantly moved towards the closed position by a spring device 28.

in which its closure section 15 seals against the valve seat 16 of the associated overflow opening. The connection between the respective associated valve inlet 32a, 32b, 32c and the associated valve outlet 33a, 33b, 33c is blocked in this case.

Each valve member 14a, 14b, 14c can be acted upon by a switching force opposite to the spring force in order to switch the valve member 14a, 14b, 14c from the closed position to the open position in which the connection between the respective valve inlet 32a, 32b, 32c and the associated valve outlet 33a, 33b, 33c is released.

The three valves 2, 3, 4 could be directly controlled designs. Preferably, however, they are operated indirectly controlled, which is the case in the embodiment. The switching force required to switch to the open position is applied fluidically here, namely by applying compressed air under a pilot pressure to an actuating piston that is designed as a unit with the relevant valve element 14a, 14b, 14c or is separate.

The application of the required pilot pressure is controlled by means of electrically operated pilot valves 35a, 35b, 35c, each of which is assigned to one of the three valves 2, 3, 4. All three pilot valves 35a, 35b, 35c are expediently connected to a common valve body

5, which has an interface 18e accessible on the outside of the valve housing 5, through which compressed air is fed during operation under a pilot pressure of preferably a maximum of 8 bar.

The pilot valves 35a, 35b, 35c expediently have electric drives in the form of electromagnets. As can be seen from Fig. 1 and 2, they are expediently attached to the valve housing. They are expediently located on the same outside of the valve housing 5, in extension of the valve chambers 6a, 6b, 6c.

The circuit diagram in Fig. 3 shows pilot valves 35a, 35b, 35c that are designed for operation with auxiliary control air. Alternatively, however, they can also be designs that are operated without auxiliary control air. The pilot valves 35a, 35b, 35c are expediently 3/2-way valves.

The pilot valve 35c of the vent valve 4 is expediently of the "normally open" type. In the non-activated state, it is held in the open position by a spring device 37, in which there is a fluid connection between the pilot channel 36 and the vent valve 4.

- ¹² "

The pilot valves 35a, 35b of the low-pressure valve 2 and the high-pressure valve 3 are of the "normally closed" type in the embodiment, with spring devices 38 specifying a closed position in the deactivated state in which the pilot channel 36 is separated from the associated low-pressure valve 2 or high-pressure valve 3. The pilot connection 38 of these valves 2, 3, via which the fluidic switching force can be imposed on the actuating piston 34, is vented to the atmosphere in this case.

The connection between the valve outlet 33a of the low-pressure valve 2 and the working channel 25 is without a check valve. The compressed air can therefore flow in both directions between the low-pressure valve 2 and the working channel 25, provided there is an appropriate pressure gradient.

In a typical operating cycle of the valve block 1, the pilot valve 35c of the vent valve 4 is first switched to the closed position, so that the pilot inlet 38 of the vent valve 4 is vented and the vent valve 4 assumes the closed position shown in Fig. 3. Due to the other pilot valves 35a, 35b having assumed the initial position and thus the open position up to that point, the low-pressure valve 2 and the high-pressure valve 3 are also in the closed position.

Now, the pilot valve 35a of the low-pressure valve 2 is activated and opened during a period of time specified for the specific application. As a result, the low-pressure valve 2 switches to the open position and compressed air at the specified low pressure enters the working channel 25 from the low-pressure feed channel 17, from where it flows to the connected consumer via the interface 18c.

Once the low-pressure application phase is complete, the high-pressure valve 3, which was previously in the closed position, is switched to the open position by activating the pilot valve 35b. Compressed air at the specified high pressure also flows from the high-pressure feed channel 24 into the working channel 25 and from there reaches the consumer via the aforementioned interface 18c. In order to prevent the compressed air from flowing into the low-pressure feed channel 17 via the open low-pressure valve 2, the low-pressure valve 2 is switched back to the closed position in this context.

Under normal circumstances, compressed air under high pressure flowing into the low-pressure valve 2 via the valve outlet 33a would impair the closing process of the low-pressure valve 2. The low-pressure valve 2 would therefore have to be closed before the high-pressure valve 3 opens. However, this time delay would cause a pressure drop in the working

- 14 -

···· · · · • * * •
•
»· · · · · • • * · • •
•
•
···· · *
· ·
· · ·
*· ·· ·
· •
··· J ·
···· · •
•
···· • · ·
·
·
· · ·· a
•
• ·
·

_ &Lgr;&Agr; _ f* &igr; ·» · ♦"· ··■*■·

channel 25 and thus also a time delay in the build-up of high pressure in the working channel 25 and thus in the connected consumer. Such an effect could be counteracted with a check valve between the working channel 25 and the valve outlet 33a of the low-pressure valve. The associated design effort is, however, relatively large.

In the valve block based on the invention, it is therefore provided that the valve member 14a of the low-pressure valve is designed with regard to its active surfaces oriented in the switching direction, which are exposed in the open position to the fluid pressures present via the valve inlet 32a and the valve outlet 33a, in such a way that these fluid pressures in the open position of the low-pressure valve 2 cause a resulting actuating force on the valve member 14a acting in the closing direction.

The switching processes of the low-pressure valve 2 and the high-pressure valve 3 are thus coordinated in such a way that the opening process of the high-pressure valve 3 is initiated at the same time as or shortly before the closing process of the low-pressure valve 2. The high pressure can thus build up in the working channel 25 almost without delay, whereby the high pressure also acting on the valve member 14a of the still open low-pressure valve 2 exerts a closing force on the valve member in the same direction as the spring device 28.

■■■•J · · »« »*· t * »

14a and actively supports the closing process. This achieves a reduction in the switching time of the low-pressure valve 2 with reduced design effort, with the result that only a small amount of high-pressure medium flows into the low-pressure feed channel 17 and thus no unnecessary air consumption occurs.

As can be seen from Fig. 2 and 4, the valve member 14a of the low-pressure valve has two first and second end sections 42, 43 arranged axially on both sides of the closure section 15. Each of these end sections 42, 43 engages displaceably in the end wall 44a, 44b of the associated outlet valve chamber 13a and inlet valve chamber 12a. Said end walls 44a, 44b can be an integral part of the valve housing 5 or, as in the exemplary embodiment, components inserted separately into the valve housing 5.

Each end section 42, 43 is enclosed in a fluid-tight manner by an annular seal 49 fixed to the associated end wall 44a, 44b.

By means of a suitable structural design of the valve member 14a, there is at least one first effective surface 45 responsible for generating an actuating force in the closing direction and at least one second effective surface responsible for generating an actuating force in the opening direction.

- JLO~

before 46, wherein the sum of the first effective areas 45 is greater than the sum of the second effective areas 46. This surface difference ensures that the prevailing pressure causes a resulting actuating force in the closing direction, i.e. in the same direction as the restoring force of the spring device 28, so that the closing process is supported by pressure force.

In the embodiment of Fig. 2, the valve member 14a has a constriction between each end section 42, 43 and the closure section 15, so that both end sections 42, 43 as well as the closure section 15 have effective surfaces relevant to the actuating force. According to Fig. 2, a first active surface 45 facing the closure section 15 is located on the first end section 42 of the valve member 14a associated with the outlet valve chamber, and a second active surface 46 also facing the closure section 15 is located on the second end section 43 of the valve member 14a associated with the inlet valve chamber 12a. The first and second active surfaces 45, 46, which are oriented axially opposite to one another in a corresponding manner, are located on the two axial sides of the closure section 15, which is designed in the manner of an annular projection. A resulting effective surface difference in favor of a resulting actuating force acting in the closing direction is achieved in that the first and second active surfaces 45, 46 provided on the closure section 15 are of the same size, while the first end section 43 of the valve member 14a is

section 42 is larger than the second effective area 46 provided at the second end section 43.

In the embodiment of Fig. 4, the valve member 14a has a constant cross-section on the side facing the second end section 43, corresponding to the cross-section of the second end section 43. The resulting actuating force in the closing direction is here due to the area difference between the sum of the first active surfaces 45 provided on the first end section 42 and on the closure section 15 and the second active surfaces 46 also provided on the closure section 15. Such a valve member, in which the second end section 43 is designed without an active surface, can generally be manufactured more cost-effectively.

It is understood that the number and distribution of the first and second active surfaces 45, 46 on the valve member 14a of the low-pressure valve 2 can be designed in a variety of ways by means of design measures.

A further advantageous design of the valve block can be seen in Fig. 3. Accordingly, a check valve 47 is inserted into the pilot channel 36 leading to the pilot valve 35c of the vent valve 4, which opens in the direction of the pilot valve 35c and closes in the opposite direction. In addition, between this check valve 47

and the aforementioned pilot valve 35c a pressure accumulator 48.

During normal operation of the valve block 1, the pressure accumulator 48 is fed by the compressed air supplied to the pilot channel 36, so that a volume of compressed air under the pilot pressure accumulates. If a fault occurs during operation of the valve block 1, for example a failure of the pilot pressure used to supply the pilot channel 36, the stored compressed air volume can be used to initiate at least one switching operation of the vent valve, by which the vent valve 4 switches to the open position so that the working channel 25 is vented for safety reasons.

If required, the working channel 25 can be coupled to several vent valves 4 in order to be able to carry out a graduated venting if necessary.

It is also possible to equip the valve block with several functional units at the same time, which have a valve structure of the type described. This means that the valve block can be used to control several consumers simultaneously and independently of one another.

Claims (15)

1. Valve block, in particular for compressed air control in the blow molding of plastic bottles, with a high-pressure valve (3) connected on the inlet side to a high-pressure feed channel (24) and a low-pressure valve (2) connected on the inlet side to a low-pressure feed channel (17), which two valves (3, 2) are connected on the outlet side to a common working channel (25) and each have a switchable valve member (14b, 14a) with which the connection between the respectively assigned valve inlet (32b, 32a) and valve outlet (33b, 33a) can be selectively blocked (closed position) or released (open position), wherein the connection between the valve outlet (33a) of the low-pressure valve (2) and the working channel (25) is designed without a check valve and wherein the valve member (14a) of the low-pressure valve (2) with regard to its in the open position the Valve outlet (33a) is exposed to fluid pressures and oriented in the switching direction, is designed such that these fluid pressures in the open position cause a resulting actuating force in the closing direction on the valve member (14a). 2. Valve block according to claim 1, characterized in that at least one first active surface (45) responsible for generating an actuating force in the closing direction and at least one second active surface (46) responsible for generating an actuating force in the opening direction are provided on the valve member (14a) of the low-pressure valve (2), wherein the sum of the first active surfaces (45) is greater than the sum of the second active surfaces (46). 3. Valve block according to claim 2, characterized in that the low-pressure valve (2) has an elongated valve chamber (6a) which is divided into an inlet valve chamber (12a) communicating with the valve inlet (32a), an outlet valve chamber (13a) communicating with the valve outlet (33a) and an overflow opening (8) connecting the two valve chambers (12a, 13a), wherein a valve member (14a) passing through the overflow opening (8) is arranged in the valve chamber (6a), which has a closure section (15) which blocks or releases the overflow opening (8) depending on the switching position and two end sections (42, 43) which engage displaceably in the end wall (44a, 44b) of the respectively associated valve chamber in a sealing manner. 4. Valve block according to claim 3, characterized in that at least one first active surface (45) is provided on the first end section (42) of the valve member (14a) associated with the outlet valve chamber (13a), at least one second active surface (46) is provided on the second end section (43) of the valve member (14a) associated with the inlet valve chamber (12a), and at least one first and at least one second active surface (45, 46) is provided on the closure section (15). 5. Valve block according to claim 4, characterized in that the first and second active surfaces (45, 46) provided on the closure section (15) are of equal size and that the at least one first active surface (45) provided on the first end section (42) is larger than the at least one second active surface (46) provided on the second end section (43). 6. Valve block according to claim 3, characterized in that at least one first active surface (45) is provided on the first end section (42) of the valve member (14a) associated with the outlet valve chamber (13a), and at least one first and at least one second active surface (45, 46) are provided on the closure section (15), wherein the sum of the first active surfaces (45) is greater than the at least one second active surface, and wherein the second end section (43) of the valve member (14a) associated with the inlet valve chamber (12a) is designed without an active surface. 7. Valve block according to one of claims 1 to 6, characterized in that the low-pressure valve (2) and the high-pressure valve (3) are each assigned an electrically actuated pilot valve (35b, 35a) responsible for the actuation. 8. Valve view according to claim 7, characterized in that the pilot valves (35a, 35b) are connected to a common pilot channel (36). 9. Valve block according to one of claims 1 to 8, characterized by at least one vent valve (4) which is connected to the working channel (25) on the inlet side and is connected to the atmosphere on the outlet side. 10. Valve block according to claim 9, characterized in that an electrically actuated pilot valve (35c) is assigned to the vent valve (4) for its actuation. 11. Valve block according to claim 10, characterized in that the vent valve (4) is of the "normally closed" type, while the associated pilot valve (35c) is of the "normally open" type, wherein a check valve (47) opening in the direction of the pilot valve (35c) and, between the check valve (47) and the pilot valve (35c), a pressure accumulator (48) are connected in the pilot channel (36) leading to the pilot valve (35c). 12. Valve block according to one of claims 1 to 11, characterized in that during its operation a low pressure of up to 16 bar prevails in the low-pressure feed channel (17), while in the high-pressure feed channel (24) a higher high pressure of up to 40 bar prevails compared to the current low pressure. 13. Valve block according to one of claims 1 to 12, characterized in that an adjustable throttle device (22) enabling a variable setting of the flow rate is inserted into the low-pressure feed channel (17). 14. Valve block according to one of claims 1 to 13, characterized in that the high-pressure valve (3) and/or the low-pressure valve (2) are each of the "normally closed" type, wherein the valve member (14b, 14a) is constantly urged in the direction of the closed position by a spring device (37). 15. Valve block according to one of claims 1 to 14, characterized in that the high-pressure valve (3), the low-pressure valve (2) and the optionally present at least one vent valve (4) have a common valve housing (5).