DE2159963A1 - Ball container and device for controlling cavitation in liquids - Google Patents

Description

Albert A. Webb, Riverside, California, V «St * A _B and J. Paul Tullis, Port Collins, Colorado, V, St.A.

Ball container and device for controlling cavitation in liquids

The invention relates to a device for controlling or suppressing cavitation in flowing liquid and is concerned in particular with a ball container and also with its interaction with a control valve in a flowing liquid system.

Cavitation generally refers to the formation, growth and collapse of vapor bubbles or vesicles in liquid if the pressure during the flow state is close to or below the vapor pressure of the liquid is reduced · the pressure reduction required to initiate cavitation may result from an acceleration of the liquid or from a non-uniform flow · In the latter Fall, turbulent eddies arise, and the pressure reduction in the center of the turbulent eddy can be of sufficient size to cause cavitation even when the mean pressure in the liquid flow is significantly higher than the vapor pressure of the liquid.

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The occurrence and extent of cavitation in flowing Liquids are determined by a large number of different influencing variables, but can be said in general terms regardless of whether it is chemicals, oil, gasoline or water, that at a chosen point within of a given system, a critical liquid or flow velocity is determined empirically at which cavitation occurs at a given pressure · Depending on the energy available and the size by which the critical speed is exceeded, cavitation can range from light to be heavy and from fine-bubble to coarse-bubble, or the system can go into supercavitation, in which the entire liquid flow is evaporated

After their formation, the vapor bubbles migrate downwards in the direction of flow, become unstable and collapse, whereby the implosion of the cavitation bubbles creates extremely high local pressures, on the order of 10 to

5 2

10 kp / cm. The process of formation and collapse of a vapor bubble can be of a very short duration, so that cavitation occurs within a valve, a Turbine or other valuable components form and can also collapse again, causing pitting formation and erosion of the component triggering it comes · On the other hand, the cavitation bubbles can depend of the various influencing variables and the degree of cavitation also in the flow or on another, in the direction of flow downward component coincide. In the case of supercavitation, the vaporized may be none for example, extend downward for a greater distance in the direction of flow before they coincide o

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The extremely high collapse pressures of the cavitation bubbles, which are dependent on the energy present in the system can be significant and earth-shaking Lead destructive force, which leads to destruction in the hydraulic system and the components, at the same time Sound and vibration effects of such magnitude occur that staying in the immediate vicinity of the system is almost impossible · With a smaller size of the cavitation a slow acting erosion force can act on the expensive hydraulic equipment, but the phenomenon can also be used to clean, mix and homogenize Liquid or used for crushing or synthesis of chemicals. In addition to the destructive The presence of cavitation can cause undesirable pressures and flow changes and can cause the Reduce the efficiency of turbines, pumps and control valves. The possibility of the emergence of harmful Cavitation in a liquid flow system is a great impediment to the design and usability of such Systems. In many cases, the use of a Large number of large and expensive hydraulic control devices required where otherwise a simple and only one Apparatus would suffice, and even then the cavitation can only be applied over a very small pressure range and in limited flow areas can be prevented · In some cases, cavitation can not be at all be suppressed to such an extent that serious erosion damage does not occur, which requires replacement of the parts · Es would be ideal if the cavitation could be controlled or limited by a simple device whose Size is relatively small and its applicability is universal, so that the device is easy to design for different installation cases and system requirements

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is adaptable, whereby the cost factor should also be favorable. Also, it would be desirable that the facility not can only be used in new systems, but also in existing hydraulic systems with sufficient Space can be installed.

It has been found that this is achieved with a container containing balls, hereinafter referred to as the ball container can be, with the ball holder either alone or in cooperation with a control valve in the Is able to control or suppress cavitation under a wide variety of system conditions and a considerable Pressure drop is reached. Ball-Containers or Ball-Containers Similar devices were used in gas systems as early as 1917 (e.g. British Patent No. 112,980) and as early as 1917 1898 in water systems (e.g. British patent specification No. 24 148), but as far as is known, these applications did not relate to the phenomenon of Cavitation in fluid flows and the construction of the proposed spherical container were not suitable for this either Purpose designed suitably.

According to the present invention, it has been found that in a given liquid flow system a spherical container of suitable construction can be used which receives the high pressure liquid flow and discharges the liquid flow at relatively low pressure, whereby cavitation in the liquid is controlled or suppressed. Such a container generally has a housing provided with an inlet and an outlet and a plurality of balls filling the housing at least along a length section and devices for fixing the balls in the housing. The balls are relative to the diameter of the housing

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ses relatively small, so that a large number of balls are required to fill the housing cross-section, and the Housing diameter and the length of the housing filled with the balls are designed so that the occurrence of cavitation in the liquid flowing through the set of balls at the designed maximum flow rate of the system is largely limited. The design depends on the system conditions and the desired result

In a special embodiment of the invention has the container housing has a conical section which gradually increases in diameter in the direction from the inlet to the outlet expanded, with the balls tightly packed in the conical section and in one or more layers on the flow side upper end of the set of balls are welded together · It has been found that the conical structure the pressure reduction caused by each ball layer in relation to the critical cavitation speeds of the Bringing liquid to a maximum at local pressures, so that the number of balls and the length of the container can be significantly reduced and its efficiency improved · To achieve maximum efficiency at simultaneous suppression of cavitation is the diameter of the container housing at the upper end on the flow side of the packed spheres made sufficiently small that a liquid velocity at the first layer of the packed spheres occurs which is close to the incipient cavitation velocity at maximum flow through the system lies"

In a further development according to the invention, the device can have a control valve which is connected to the high pressure side is, and at its outlet or on the flow side

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The lower end of the ball container is connected: · The housing diameter and the length of the housing portion containing the quantity of balls are designed so that cavitation is largely suppressed at the control valve over a range of flow rates that the maximum flow rate of the System includes. In a further development according to the invention, the control valve has a hydraulic state actuator and devices responsive to the system for scanning the hydraulic state in the direction of flow behind the packed balls in the container

The ball container according to the invention and its interaction with a control valve is in the following description of an embodiment in conjunction with the drawing explained in more detail, namely shows:

Fig. 1 is a side view of a high pressure test setup in a water system in which the ball container with a control valve cooperates;

FIG. 2 is a diagram showing the interaction of the ball container and the control valve shows when the valve is opened differently;

Fig. 3 is a diagram showing the empirical determination of cavitation in a given system shows;

FIG. 4 shows a modified longitudinal section through the ball container from FIG. 1; FIG.

Figure 5 is a sectional view taken along line 5-5 in Figure 4;

Fig. 6 is a partial sectional view taken along line 6-6 in Fig. 5; and

FIG. 7 is a sectional view taken along line 7-7 in FIG. 4.

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In Pig. 1 shows a test arrangement built into a high pressure water system, in which a 4 inch inlet pressure line 10 is anchored in a concrete foundation 12 and leads to a manually operated valve 14.A 4 inch outlet pressure line 16 is at some distance from the inlet pressure line 10 in the concrete foundation anchored and connected to a similar valve valve 18 so that various apparatuses can be connected between the valve valves 14 and 18 for experimental and observation purposes The outlet of the valve 14 on the inlet pressure line 10 carrying the high pressure is connected via a 4-inch-2 inch reducer 20 to the inlet 22 of a control valve 24, which is formed by a two-line ^f Roto-Disc ¹ 'valve from the applicant, the structure of which is from U.S. Patent 3,424,200 · The Aus Let 26 of the control valve is connected to the inlet of a spherical container 28, the outlet of which in turn is connected to the inlet of the valve slide 18 by means of a four-inch steel pipe section 30 38 an intermediate support is formed.

The control valve 24, as shown in Pig * 1, has an electric actuator 40. At the actual The experiment in the system was manually operated electrical actuator used, but electrical or hydraulic actuators are also available Available, which automatically control the valve opening depending on the state of the hydraulic system, and in FIG

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is therefore a line signaling the water pressure 42 shown, from the actuator 40 to a downstream leads behind the balls in the container and in the present case to a pressure connection is guided at the bottom of the outlet portion of the container itself. Usually cavitation acts on a pressure or Flow measurement behind a control valve, and the present system offers the advantage in this regard that cavitation is suppressed at this nearby point

When the pressure in the liquid is sufficiently reduced, gas diffuses out of the solution and collects in bubbles Although this condition has nothing to do with cavitation directly, it is in terms of one behind the container arranged monitoring device, e.g. a flow meter, is essential · Therefore, on a gas pressure connection 48 on the top of the container at a point below the balls on the flow side is a common one Gas vent valve 46 provided for venting such gases *

In the system shown, it is essential that the ball container is arranged behind the control valve, so that at the valve a maximum flow control with simultaneous Suppression of cavitation in the valve can be done. If the container were arranged in front of the valve, this would only have a very low throttling capability without cavitation occurring at high flow rates. When ordered of the container behind the valve, this generates sufficient back pressure at high flow rates, see above that a high pressure drop can be generated across the valve without the valve being subject to cavitation. The local

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before removal of the container behind the control valve can also be essential. In addition to the obvious advantages of the compactness of the system, convenience operation and the desired short signal line can, under certain conditions, be followed by an immediately following Arrangement can also be advantageous in terms of cavitation. However, if there is no cavitation on the valve is to be expected, the container can be arranged at any distance behind the valve with respect to this point of view will. However, if under certain flow conditions at certain sizes of the valve opening cavitation is to be expected, the container should be positioned far enough downwards in the direction of flow so that the Cavitation before hitting the foremost layer of balls of the container collapses · This distance depends on the valve opening and is between two to five times the inner diameter of the outlet 26 of the Control valve, this distance S from the downstream end of the neck portion 50 of the valve to the upstream end The end of the balls in the container is measured · For this purpose it is called the end of the neck portion of a valve and the point at which the neck portion constriction into the tubular portion is assumed as the beginning of the outlet passes, which is normally provided as an outlet in conventional valves. On the other hand, a relative flat velocity profile typically at least a distance of about five times the diameter. if so only very heavy or super cavitation under certain flow conditions and valve opening sizes is to be expected temporarily, for example when opening or closing the valve, the container should do so be arranged close to the valve that no full cavitation develop because of the balls in the intermediate zone

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can so that the supercavitation collapses before it can develop completely, and vibrations are suppressed · The distance S required for this state is about two times the inner diameter of the valve outlet «If under certain conditions there is noticeable cavitation is to be expected, and especially when the distance S is within a distance of five times the diameter, it is best to use the first and the next upstream layers of balls made of a highly erosion-resistant material, ζ · Β · corrosion-resistant Steel, with the balls welded to each other and to the container housing.

Taking all factors into account, it was found that the optimal distance is about five to ten times the diameter.

As can be seen in Figure 4, the housing is the ball container is a welded steel structure and consists of a removable inlet section 52, a conical or frustoconical section 54, a cylindrical Haitabschnitt 56 and an outlet section 58 »wherein the The direction of the liquid flow is indicated by the arrows drawn in the figure.

The detachable inlet section 52 has an upstream side Mounting flange 60, an outflow-side mounting flange 62, a smooth or streamlined inlet 64 two inches in diameter and a conical one Neck section 66, which is smooth and stepless to the outflow End of inlet 64 connects · The neck section 66 of the inlet section runs in Sfcrömungs ~ direction through the fastening flange 62 and end *> t to be *

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nem downstream end 69 at the conical section 54 in such a way that that a soft and continuous cone is formed, the diameter of which gradually increases in the downstream direction grows, with the neck portion 66 forming the truncated apex of the cone.

The neck section 66 of the inlet section receives the first or upstream four layers 71 of a set of relatively small balls 70 which fill the conical section of the housing and which are exposed at the upstream end.These first four ball layers are matingly interlocking and arranged in planes in the transverse direction of the housing, wherein the center line 72 of the first layer is arranged at a point in the neck section 66 at which the inner diameter of the neck section D _{u has} a predetermined value , and wherein the fourth downstream layer is approximately flush with the flat planar surface 68 which forms the downstream end of the neck section. The balls in the first four layers are welded or fused to one another and to the housing, whereby there is essentially point contact, so that there is no significant narrowing of the passage through the interlocking ball layers.

Cast iron grinding balls were used in the construction of the test container a diameter of about 12.7 mm, and for the first four layers in the neck portion of the inlet portion the balls were coated with copper to a thickness of about 0.0128 mm and heated in the furnace so that they fused or welded to each other and the wall of the neck portion. Cast iron abrasive balls are there, though not ideal, relatively cheap and readily available, and suitable for many applications.

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As shown in Figs. 4 and 7, the densely packed spheres are meshed with each other in polygon-like patterns a layer of spheres does not stand along all of their points Diameter in contact with a circle, leaving marginal gaps such as those shown at 74 in FIG. 4 · Improved performance of the critical four first layers 71 can be achieved when the balls are first be welded together in a larger packed configuration and then twisted off or so be milled so that they fit exactly into the neck section 66, whereby ideal positions with certain partial spheres lying on the circumference (e.g. partial sphere 76) are obtained. If desired or necessary, the entire amount of balls in the container can be built up in this way.

The conical housing section 54 of the container merges with the conical neck section 66 of the inlet section 52 so that a continuous, truncated cone is formed. The conical section has an upstream fastening flange 78 to which the downstream fastening flange 62 of the inlet section is detachably screwed, a seal 80 being inserted between the flange surfaces that come into contact with one another for sealing purposes. The conical portion 54 widens to a predetermined diameter D. at the downstream end, so that the set of balls 70 between the center lines 72 and 82 of the first and last, ideally packed ball layer has a length L. With given inflow and outflow diameters D _u , D. the angle θ of the cone is determined by the length L, which in turn is determined by the number of layers of balls arranged on top of one another and the diameter of the balls.

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The cylindrical holding section 56 is at the downstream end of the conical housing section 54 by welding connected and filled with a lot of tightly packed, larger Haitekugein 84 attached to the last or The position of the relatively small balls 70 on the downstream side are in contact. As also shown in FIGS. 5 and 6, the Retaining balls 84 have a downstream or end ball position 86 which forms the base of a pyramidal stack 88 of retaining balls which are welded together, is centrally located within the Haitekugel quantity and in the direction of the inflow v / eist. A retaining plate 90 with a central hexagonal is located on the downstream layer 86 of the retaining balls Opening 92 on · A number of ribs 94 are welded into the opening and run parallel and spaced apart from each other across the opening, so that it is divided into a plurality of openings. The retaining balls in the End positions 86 are arranged close to one another and in a pattern set which has rows of adjacent balls such that their center lines with the ribs are aligned as shown at 96 with the balls of the rows in point contact with and against the ribs are welded in place · This provides stable support for the last layer 86 of the pyramidal stack 88 of the retaining balls 84 created, while the flow of liquid is only minimally obstructed, because such a Insertion of balls into the openings between the ribs is prevented

A shoulder plate 98 is provided on the inflow side as an aid for production and as a further strong support applied to the holding plate 90 and welded to it. The shoulder plate 98 has a hexagonal opening 100 on, which is larger than the aligned hexagonal opening 92 in the holding plate 90, so that an inflow

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tig lying on the holding plate, the circumference of the hexagonal The circumferential shoulder 102 surrounding the opening 92 is formed The end position 06 of the retaining balls is in such a pattern gasp barks, that 'it exactly in the hexagonal opening 100 fits into the Schulfcerplafcte 98 * on dle.se V / ei ;; e forms the combination of the shoulder plate and the holding plate 90 a recessed grid which fits together with the end position 86 of the retaining balls. In the manufacture of the test container, cast iron squint balls of one diameter were used 3.175 cm used as retaining balls. The pyramidal stack 88 was formed and on the shoulder and retaining plate 90 welded by the balls in a thickness of 0.0127 mm coated with copper and in the furnace together and soldered to the shoulder plate and the retaining plate

As is easy to see, the support structure must be made very stable in order to prevent any Ball is entrained in the flowing liquid, while at the same time the liquid flow is minimal or to hinder in known size. The support structure shown supports the downstream end of the set of small balls 70 and is in this way a method to the hand by which a holding plate with a A multiplicity of openings can be used without the problem of the small balls getting into the Set openings or block them and thereby change the flow properties, as is the case with known container designs the case is · By fixing by means of the retaining balls in point-like contact, the Flow is not significantly inhibited by the last layer of the small balls, and neither of the balls can be either of the Reach openings in the retaining plate.

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The outlet section comprises a bowl-shaped end piece 104 which is attached to the abströtseiten end of the cylindrical holding section 56 is welded on. An outlet port 106 with an inside diameter of 4 inches is centered on the end piece welded on and carries one with its downstream side End of final mounting flange 108

As best seen in Fig. 4, the container may be provided with a pressure port 110 which is upstream of the first layer of balls and communicates with the interior of the inlet 64 of the inlet section. A similar pressure port 112 is immediately behind last location of the relatively small balls. The further pressure connection 44 is arranged on the underside of the outlet section 58 and is in communication with the interior of the bowl-shaped end piece 104, and the pressure gas connection 48 is arranged in the same position, but on the opposite side of the container, which in operation is the top of the The container should be, as the gas bubbles tend to collect at the top. The pressure connections dJ.enen in connection with (not shown) pressure gauges for monitoring pressures at the essential points of the container during operation in order to determine the performance of the container under different flow conditions or, in the case of the downstream pressure connection 44 _f , they can have control functions if they are connected to hydraulic control devices, for example via the signal line 42 to the actuating element 40 of the control valve. The pressure connection 44 on the underside also serves as a drain of the container. When not in use, the drainage pipes and the gas pressure connection are closed with stoppers, as shown, for example, in FIG

? 0 9 8 2 7/0 G 0?

When inserting the loose retaining balls 113 into the container these are filled through the upstream end 69 of the conical section 54, and they surround the pyramidal Stack 88 · The container body is then shaken or pounded with a hammer until the retaining balls are tightly packed and cannot be moved any further. After the cylindrical section 54 is approximately up to its upstream end is filled, the balls become 70 of 12.7 ran in diameter into the open end of the conical Housing section 54 is filled and the housing is again caused to vibrate or hit with a hammer until until these balls lie against the larger retaining balls and are packed so tightly that they cannot move any further move. Balls with a diameter of 12.7 mm are then filled in until the conical housing section 54 is filled to about even at its inflow end, whereupon the removable inlet section 52 with the first four layers of balls welded together is attached to the conical section by being downstream Fastening flange is screwed to the upstream fastening flange of the conical section 54. the The relatively large retaining balls 84 and the relatively small balls 70 will not, as expected, be exactly those in FIG. 4 occupy the stacking layers shown, which are shown as such for illustration purposes only, unless the balls are welded together · The small and the large balls will be in some of the free spaces along the Perimeter of the layers in Fig. 4 penetrate or the layers will spread out to fill some of these free spaces, and some of the small balls can be in certain adjacent free areas in the set of larger balls as shown at 116 and 118, for example. In any case, both the balls are in the conical and

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the balls in the holding section are approximately in positions and are closely matched and immovable

The relatively small balls filling the conical portion of the container must have a diameter which is relatively small compared to the diameter of the housing so that a large number of balls are required to form a given layer filling a cross section of the housing. Seven adjacent balls of one layer were sufficient, but nineteen balls were used in the test container for the upstream layer at the point where the housing diameter D _{u was} 6.86 cm. A choice of the balls with the smallest possible diameter appears advantageous, but the diameter must be chosen at least large enough that the balls do not act as a filter, so that the passages between them tend to clog as a result of deposits from the liquid medium flowing through them, and the The cone angle θ should be kept small.

It is necessary to keep the cone angle θ relatively small in order to ensure a uniform flow through the inlet portion of the housing without delimitation occur at the points where the cone widens from the inlet 64. When the test containers were obtained satisfactory results with an angle θ of about 15.5 °, but this angle can be increased however, performance retention is uncertain. A reduction in the diameter of the balls by 12.7 mm to 6.35 mm would considerably increase the cone angle for the same number of ball layers. Considering the above * considerations it was found that the balls should have a minimum diameter of about 12.7 mm,

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while larger balls can be used in conjunction with the corresponding housing diameter, thereby increasing the length the number of balls 70 in the housing is increased accordingly.

It is possible to make the dimensions of the balls variable, so that the gap ratio gradually increases towards the upstream side Portion of the container decreases, however, this design is not a satisfactory replacement considered a conical container because it is difficult to manufacture and control, its operation only difficult to predict and the container tends to act as a filter and clog.

The small balls 70, like the retaining balls, should be at least approximately spherical and ideally should they are made of a very hard material that protects against erosion and corrosion attack by the liquid medium is highly resistant · During the trials were because of its easy availability and low cost Cast iron grinding balls were used, and with these balls was made performs reasonably cost-effectively in a number of fluid system applications; However, better balls are also available, e.g. rejected ball bearing balls or ceramic grinding balls, for the methods of welding or soldering to one another and to the housing without significant reduction the passage through the spherical areas are given.

There are of course a wide variety of fluid flow systems that in which the flow velocities or the pressure differences are high enough to to use the new ball container with advantage, and in

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every given system has a large number of variables, which affect cavitation. Some of these variables are, for example, the pipe diameter, the upstream side Pressure, the downstream pressure, the properties of the liquid medium, e.g. its density and viscosity, the ambient temperature and the vapor pressure of the liquid at this temperature, the air pressure, the gas content the liquid, the general size and shape of an obstruction, constrictions or bends in the flow path in the system, e.g., the size and shape of a control valve opening with various opening states of the valve, etc. Fortunately, in most systems a large number of these variables have a known value and remain constant or essentially constant, so that for For design purposes an average of many variables can be used · For a given system with given Liquid in which the container is to be inserted at a point where the ambient conditions are known the main variables are the pressure changes and the flow rate changes and, if a given control valve Used in conjunction with the container, changes in the size of the valve opening. Usually is the upstream pressure is known and roughly constant, and that The system is designed in such a way that it delivers a maximum volume flow at a considerably lower downstream pressure, whereby Cavitation is controlled or suppressed.

When designing the container for the experiment in the water system shown in FIG. 1, a maximum flow rate of approx. 3,000 l / min. at an essentially constant upstream pressure P _u of 46.4 kp / cm (660 psig), these values being determined by the pressure in the inlet pressure line 10 in connection with a fully open

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The aim was to control this water over a large volume flow range by means of the control valve 50 to an essentially constant discharge-side pressure P _d of 1.41 kp / cm. Based on the fact that the flow rate is equal to the flow rate divided by the area of the liquid flow, it was found that a pipe with an internal diameter of 2 inches resulted in a flow rate of just under 25 m / sec, whereby a high velocity should not lead to cavitation caused only by the acceleration of the water in a steady flow at local pressure.

If the container is in a control valve on the flow side is used before the container-having system, as shown in Fig. 1, must be designed next a control valve can be selected so that all of its components with respect to the maximum working pressure are dimensioned with a safety factor in an appropriate manner, the valve being designed for high speeds should be in order to keep the required size of the valve for the maximum flow rate as small as possible, whereby Usually the cost of the valve and its accessories are reduced · There are not many valves that come with work at a water speed of about 25 m / sec can. "Straight or free flow" type valves or gate valves are usually best. It will the term "free flow" is applied to such types of valves where the flow is not tortuous but essentially straight through the valve, and where the valve has essentially no constriction when fully open and corresponds to the inner diameter of the conduit. A free-flow valve also generally allows

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A good example of such a valve is the ^{applicant's fl} Roto-Disc "valve shown in FIG. 1, with a neck section 50 with an inner diameter of 2 inches, which corresponds to the line diameter when fully open.

Another reason for choosing the valve type and size which enables the desired mass flow at high speed is that the flow rate in the valve outlet near the critical cavitation velocity of the liquid at the operating pressure should be in the first ball position in the container in order to ensure that it is full Take advantage of the maximum energy that can be distributed from the first layer of the balls without cavitation, so that a minimum of reductions or increases in the inside diameter of the inlet portion of the container or others Lines in front of the first ball layer is required to maintain this speed.

The next step in the design process is to determine the size of the balls to be used and the size of the container section that will receive the balls. The size of the balls has already been discussed; Based on the use of a ball with a diameter of 12.7 mm in the test container, the diameter D _{u of} the upstream position of the balls, the diameter D ^ of the downstream position of the balls and the length L required to achieve the desired pressure reduction at maximum flow rate had to be calculated will.

Laboratory measurements are carried out to calculate the upstream and downstream diameters D _{u and D.}

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the critical cavitation speed V at different Determine operating pressures. Fig. 3 essentially shows such a laboratory fixture. ZtBa an accelerometer on the outside is connected to an opening to be examined, the size of the measurement output increases when the flow velocity the liquid increases at constant pressure. The measurement is usually made by measuring the velocity of the liquid carried out in the direction of flow upstream of the opening at constant upstream pressure, with changes the flow rate can be obtained by adjusting the downstream pressure, although the measurement also - at least for the purpose of determining the onset of cavitation - can be carried out in reverse

When the speed increases at constant pressure, Initially, the value of the measured variable also increases gradually because of the increasing flow noise, until it reaches a point at which the measured value suddenly rises, this point being referred to as the critical cavitation velocity V. is the point of incipient cavitation, as can be seen from the curve shown in FIG. Another increase in the flow rate leads to faster increase in cavitation and eventually when enough energy is contained in the system is, to supercavitation, at which the measured value when the cavitation is some distance in the direction of flow collapses downwards, can and often does, as it continues from the collapse area away. The critical cavitation velocity changes with pressure and it has been found that the Point of incipient cavitation at lower speeds occurs when the local pressure is reduced

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When designing the test container, the critical cavitation speed was based on previous test results Assumed 12.5 m / sec at a local pressure of about 46.4 kp / cm (660 psig). For the outflow side Layer of the balls on the holding device, the critical cavitation speed was measured at about 2.2 m / sec from the last position at an assumed local Assume a pressure of 1.41 kgf / cm (20 psig) exiting stream. Using the aforementioned relationship between flow rate and area, it was calculated that the inflow term diameter D about 6.86 cm and the downstream side Diameter D ^ had to be about 17 cm.

With regard to the outlet-side diameter D ^, however, to have a safety factor, a value of 10 inches was used, taking into account the design of the holding device was and was based on the theory that in the worst case, the holding device as a device can be seen that blocked part of the area of the last layer of the small balls. This is called Reason considered that the entire of the grid-like opening 92 formed in the holding plate 90 on the drain side free area in the area was made roughly equal to a circle about 17 cm in diameter, as originally calculated for the downstream layer of the small spheres at D ^ became.

With the inflow and outflow diameters D _u and D ^ of the cone fixed at 6.86 cm and 25.4 cm, the length L of the amount of spheres required to achieve the necessary pressure drop was then determined using the following energy equation whose left side is the energy in the water ^{in kp / cm 2 χ 0.0703 (psig)}

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upstream system minus the energy of the system the downstream side, while the right side in kp / cm χ Oι0703 (psig) the sum of the in the respective positions of the Spheres in the set of spheres of annihilated energies:

148.8 Of Γ? * ^P vc

ζ ⁿ γ * \ Γ , (D
η = 1 L

0.866

The following values appear in the energy equation: Q «Volume flow in Ο. / Min) χ 3.79 (gallons / min)

D - inner diameter of the cone at the center line the upstream position of the small balls in cm χ 2.54 (inches)

D ^ - Inner diameter of the cone at the center line of the last layer of small balls in cm χ 2.54 (inches)

P _vc * Pressure on the inlet side at the tank inlet in (kp / cm ² ) χ 7.03 χ 10 ~ ² (psi)

P ^ m Downstream pressure from the container in (kp / cm ² ) χ 7.03 χ 10 ~ ² (psi)

d _B = diameter of the small balls in cm χ 2.54 (inches)

N β number of layers of small spheres, equal to L: 0.866 d _ß

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L »Distance between the center lines of the first and last layer of the small balls in cm χ 2.54 (inch)

K „β constant of the sphere, which is used for spheres with a Diameter of about 12.7 mm has the value 0.0157 »

By inserting the values Q «3» 000 1tr / min, D ■ 6.86 cm,

2 2

D, «25.4 cm, P« 46.4 kg / cm and P. β 1.41 kg / cm in the On the left, the energy equation gives a pressure drop of approximately 46 kp / cm over the volume of the small spheres in the container. The summation was made by iteration with the assumption of different values for L that are an integer Value for the number N of ball layers was solved, the iteration being repeated until a correct one A value was found at which the summation of the pressure drops over the successive layers added up to 46 kp / cm, when the number of balls given on the left side of the equation has been calculated. It turned out to be this was the case with a length L of about 33 cm, so that the value N resulted in 30 plies, the calculation resulted in a pressure drop on the first layer of spheres of about 13.3 kgf / cm, while the pressure drops on the subsequent ones Layers quickly decreased until they were on the order of about 0.07 at the last or 30th position

2
kp / cm.

The experimental vessel was designed according to the above calculations and it performed remarkably well when taken into account that the pressure drop across the holding means and in the outlet portion of the container has been neglected which should be added on the right hand side of the energy equation in order to

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To calculate se · During the measurement, this pressure drop was

about 1.76 kgf / cm · The performance was also due to other reasons remarkable because the critical cavitation velocities were taken from earlier test results and have not been re-determined in the laboratory · P

2 and P "_ were both assumed to be constant at 46.4 kp / cm,

VC

when the control valve was fully openP varied actual-

2 2

mainly from 50.6 kp / cm to 47.3 kp / cm with a valve opening of 5 % to 100%, with P. correspondingly from 1.41

P 2

kp / cm was changed to 1.69 kp / cm · The value for the ball constant K _ß was determined from measurements on cast iron grinding balls with a diameter of 12.7 cm arranged in close packing in a cylinder with a diameter of 10.16 cm It is unclear whether the spherical constant changes depending on the diameter of the spheres and the diameter of the container at the relevant layer ·

For the calculation of K "the following spherical constant - Equation used, the readings of the flow through a densely filled with balls of a diameter of 12.7 mm Containers were used:

^(p u * ^P d ^} ° » ^{866 d} b ° ⁴

n * 5

^B LQ ²

In the spherical constant equation, the upstream pressure P _{u was} 37.9 kp / cm, the downstream pressure P _{d was} 3.54 kp / cm, the ball diameter d ^ 12.7 mm, the housing diameter D 10.16 mm, the length L. of the sphere volume 43.2 cm and the volume flow Q was approximately 1,710 ltr / min,

209827/0607

As can be seen from the energy equation calculations, in which the pressure drop at the last layer of the small spheres was in the order of magnitude of 0.07 kp / cm, would be Using a cylindrical container instead of a conical container, a number of layers from 600 to 700 ball layers be required to achieve the same pressure drop, while conical containers only require 30 layers if both work with equally strong cavitation

2 shows a diagram which shows the actually measured pressure value Ρ _γ at different valve openings. "P" was measured at the point shown in FIG both were the same · The measured volume or volume flows are also given in (ltr / min) χ 3.79 (gallons / min), which correspond to the various curve points indicated in the drawing. The pressure difference at the valve CP- P _vc > and the pressure difference at the container (P _vc - P _d ) can only be taken approximately from the FIg * because there are minor deviations in the upstream and downstream pressures are not taken into account.

The system shown in Fig. 1 was equipped with speed gauges (not shown) and pressure gauges (not shown) at various locations including those indicated at P _u , P _vc and P ^. The flow measurements were made in the direction of flow behind the container.

During the trials, the accelerometer readout stayed

2 2

in the range from 254 m / sec to 508 m / sec from the peak value

209827/0607

ssu apex, with the exception of the 20 to 25 % valve opening range, where some measurements are 1,270 m / sec

2
up to 2,540 m / sec. This was about the percentage valve opening at which about half the pressure drop in the system at the container was reached, which indicates the possible presence of a certain fine-bubble cavitation on the valve - the gas pressure connection 48 also removed larger amounts of air.

In contrast to this, the system would otherwise have been a flow system with supercavitation. With the container removed, in otherwise the same system at an upstream pressure of about 49.2 kp / cm, pressures at the valve outlet were measured, ranging from a vacuum of 288.6 mm Hg at 15% valve opening to a vacuum of 432 mm Hg at 40% valve opening varied, with the volume flows ranging from 1,685 ltr / rain to 1,923 ltr / min at the corresponding valve openings.Without the container, the vibration and noise level in the immediate vicinity was so great that it was not considered acceptable or desirable to keep the valve opening at 40 % or to open the valve further

A slight cavitation may also have occurred with valve openings in the range of 10 % and below, but the test setup was such a strong steel construction and the flow noises were so great that, regardless of any cavitation present, there was no sufficient energy level available for the measurements expressed.

From Fig. 2 it can also be seen that in an embodiment in which the volume flow at considerably lower valves

209827/0607

valve openings than is achieved with 100% valve opening, ZeB. at 30% opening, and with a suitable design of the container, the valve can be opened to 100% and then a sufficiently increased flow rate and a pressure drop across the container occur, so that cavitation occurs in the container, which is necessary for the removal of deposits and deposits, ie can be used for cleaning. This appears practical because, as shown in the diagram according to FIG. 2, the maximum flow occurs in a valve with valve openings below 40 % .

2098 27/0607

Claims (1)

Claims Iy plant for supplying a liquid with relative low pressure from a high pressure liquid supply preventing the occurrence of cavitation, characterized in that the system has a spherical container (28) has «its with an inlet» and an outlet (64,106) provided housing (52,54,56,58) at least over one Part of its length is filled with a volume of balls (70), and that means (84-100) for fixing of the balls (70) in the housing (52,54,56,58) are provided, the diameter and the length of the ball-filled Housing section are designed in such a way that cavitation in the system is suppressed to a significant extent 2 «Plant according to claim 1, characterized in that a control valve (24) is provided, the inlet of which is connected to the High pressure liquid supply and the outlet (26) of which is connected to the inlet (64) of the spherical container (28), and that the diameter and length of the ball-filled Housing section are designed so that the cavitation is suppressed over a range of flow rates, the includes the maximum nominal flow rate of the system 3 · Plant according to claim 1 or 2, characterized in that the diameter (D _u ) of the container housing (52, 54, 56, 58) is kept so small that at the maximum nominal flow rate of the plant, a flow rate close to the speed of the cavitation begins at this point, and that the container housing widens in diameter in the direction of the discharge 209827/0607 4, system according to claim 2 or 3, characterized in that the system is designed so that the maximum nominal flow rate is reached when the control valve (24) is only partially open, so that the control valve (24) to generate a conscious cavitation in the Container (52,54,56,58) and can thus be opened further to clean the balls (70) 5 · Plant according to one of claims 1 to 4, characterized in that the devices (84-100) for fixing the balls (70) in the housing (52,54,56,58) with a multi- ^ number of openings are provided, the total area at least approximately equal to that at the downstream end of the volume of the balls C70) is the required cross-sectional area, so that the system starts at the relatively low pressure and the maximum nominal flow rate at or in the vicinity Cavitation works. 6. System according to one of claims 2 to 5, characterized in that the control valve (24) is an actuating element which responds to the hydraulic state of the system (40) and a device (e.g. 42) for sensing the hydraulic state in the direction of flow behind the volume of the balls (70) la container (28) · | j 7. Plant according to claim 2 to 6, characterized in that the inflow-side end of the volume of the balls (70) in the direction of flow at a distance that is approximately the same corresponds to two to five times the inner diameter of the outlet (26) of the control valve, behind the passage (66) of the Control valve (24) is arranged 8 * ball container for the system according to claim 1, characterized characterized in that the portion filled with balls (70) 209827/0607 of the container (28) with an increasing diameter in the outflow direction is conical 9. ball container according to claim 8, characterized in that that the diameter of the housing (52,54,56,58) of the container (28) at the upstream end of the volume of the balls (70) is so small that there is a flow velocity at this point at the maximum nominal flow rate of the system sets close to the speed of the onset of cavitation 10. ball container according to claim 8 or 9, characterized in that that the diameter of the housing (52,54,56, 58) at the downstream end of the volume of the balls (70) is dimensioned so that there is a flow velocity at this point at the maximum nominal flow rate of the system sets in the vicinity of the incipient cavitation. 11. ball container according to one of claims 8 to 10, characterized characterized in that the container (28) has a gas pressure connection connected to the interior of the housing (52,54,56,58) (48) on the upper side and at a point located in the direction of flow behind the volume of the balls (70) of the housing, and that the gas pressure connection (48) a gas vent valve (46) is connected. 12 · spherical container according to claim 8, characterized in that that the housing (52,54,56,58) has a conical section with in the direction from the inlet (64) to the outlet (106) gradually increasing diameter and a removable inlet section (52), and that the inlet section (52) has a neck section (66) forming the inflow end of the conical section of the housing 209827/0607 13 · Ball container according to claim 12, characterized in that that the balls (70) in the neck portion (66) has a layer of balls (70) welded together, which in the is arranged substantially level with the downstream end of the neck portion (66). 14. Ball container according to claim 12 or 13, characterized in that that in the neck portion (66) a plurality of adjacent stacked and welded together Layers of balls (70) is included 15. ball container according to one of claims 12 to 14, da- ^ characterized in that the devices for plaguing the balls (70) have a plurality of in the housing (52,54,56,58) has relatively large balls (84) arranged on the outflow side behind the small balls (70) and resting against them, and that devices for fixing the relatively large balls in the housing (52,54,56,58) are provided. 16 · ball container according to claim 15, characterized in that a plurality of the relatively large balls (84) with one another is welded 17 · ball container according to claim 15 or 16, characterized denotes overall .m that the relatively large balls (84) has a downstream location (86) and a pyramid-shaped stack (88) of welded-together beads (84), wherein the The downstream layer (86) of balls (84) forms the base of the pyramidal stack (88) 18. Ball container according to one of claims 15 to 17, characterized in that the devices for fixing the relatively large balls (84) in the housing (52,54, 209827/0607 56,58) a holding plate provided with an opening (92) (90) and a plurality of spaced apart ribs (94) extending across the opening. 19. Ball container according to one of claims 15 to 18, characterized characterized in that the ribs (94) extending over the opening (92) are arranged parallel to one another, that the large balls (84) in the downstream position (86) are packed tightly together in a pattern comprising rows of adjacent spheres, which are aligned with the ribs (94) that the balls (84) do not sit in the openings formed between ribs, and that the balls (84) are fixed in this pattern 20. Ball container according to claim 19, characterized in that the circumference of the downstream layer (86) of relative large balls (84) has a polygonal configuration, and that the opening (92) in the downstream retaining plate (90) has a similar polygonal shape and is upstream a shoulder (102) is formed around the circumference of the opening (92) of the holding plate, which is attached to the balls (84) in the circumference the downstream position ("86) applies 21. Ball container according to one of claims 8 to 20, characterized characterized that at least some of the small Balls (70) are welded together 22 · Ball container according to claim 21, characterized in that that the diameter of the housing (52,54,56,58) is many times larger than the diameter of the balls (70), and that the balls (70) are at least approximately spherical and have a diameter of at least about 12.7 mm. 209827/0607 2Ί59963 23. Ball BehSlfcer according to claim 8, characterized in that the balls (70> in close packing and in the housing (52, 54,56 * 58) are immovably arranged that the diameter of the housing is several times greater than the diameter of the Balls (70), and that the first or inflow-side layer (71) of the balls (70) is welded in place 24 · Ball container according to one of the preceding claims, characterized in that the balls (70) have a relatively small diameter, so that a large number of balls is necessary _{to fill the cross-sectional area of the housing (52, 54 r} 56 _{r 58)} , and that the volume of the balls (70) is exposed at the upstream end 209827/0607 to Blank page