High pressure fluid pump with poppet valve

Abstract: An outlet valve for a high pressure pump which is designed to alleviate "sticking" of the moveable valve element. An annular recess is formed at a transitional flow area where high pressure fluid flows forwardly and then radially outwardly between contact surfaces of the valve element and a valve seat member. It is believed this alleviates a problem of separated flow at the transition area which would effectively decrease the flow area and cause a localized pressure reduction which would delay proper opening of the valve element. Also, other configurations are shown for tripping the boundary layer to avoid separation, and other configurations to alleviate the same.

Description: BACKGROUND OF THE INVENTION a. Field of the Invention The present invention relates to a valve, and more particularly to a valve adapted for use in a high pressure pump, such as a poppet valve to receive flow from a high pressure piston. A pump as described in the preamble of claim 1 is known from DE-A-28 35 47& In the type of valve in the known pump the problem is that when the very high pressure pump is about to open there would be a delay which causes a pressure spike. In the prior art devices it was thought that one of the reasons for this was that the area that is exposed to the pressure is smaller than the area on the downstream side where the back pressure is exerted over the greater area. b. Background Art High pressure pumps are utilized in a variety of applications. In such pumps a fluid is brought to pressures as high as 10,000 psi [68947,6 kPa] or even as high as 100,000 psi [689476 kPa] or greater. This pressurized fluid, (generally water) can then be discharged through a nozzle as a high velocity stream of water to accomplish functions such as cutting, abrading, etc. A common arrangement of such a high pressure pump is to have a plunger or piston which reciprocates in a cylinder on an intake stroke where the plunger retracts to draw water into the cylinder chamber, and a discharge stroke where the plunger acts against the water to discharge it at a very high pressure. An outlet valve is positioned at the end of the cylinder to receive the flow of high pressure fluid. On the pressure stroke, the outlet valve opens to receive the flow of high pressure fluid, while on the return stroke of the plunger, the outlet valve closes to prevent the pressurized fluid from returning into the cylinder with water flowing into the cylinder through an inlet valve. A typical valve used in this application is a poppet valve, where the valve element has a transversely extending contact surface which fits against a matching contact surface of the valve member to close the passageway leading from the high pressure chamber. A spring or other means is used to urge the valve element toward its closed position. On the pressure stroke of the plunger, the pressure in the cylinder chamber moves the valve element to its open position to permit the pressurized fluid to flow around the valve element to an accumulator or manifold to be utilized in some operation, such as forming a high velocity jet. One of the problems associated with such poppet valves is that there is sometimes a delay in the proper opening of the valve, which is commonly described as "sticking" of the valve. Desirably, when the force resulting from pressure of the fluid within the cylinder chamber reaches a level just at or above the combined force of the pressure downstream of the poppet valve and of the biasing spring, the poppet valve should open so that there is a flow of fluid from the chamber to a down stream location without any substantial discontinuity in fluid pressure. However, if there is a delay in the proper opening of the valve, there can be a pressure spike where the pressure in the cylinder continues to rise to an undesirably high level. Even without such pressure surges, the fluid is pressurized to a very high level, thus imparting substantial loads on the components of the pump assembly. Thus, pressure surges above the desired level place rather severe stresses on the components of the pumping assembly. Some of the prior art approaches for alleviating the problem of delay in opening of such poppet valves are based on the belief that the delay is caused by sealing over too large an area. To explain this further, if the area of the poppet element that is exposed to high pressure on the downstream side is greater than the area of the poppet element that is exposed directly to fluid pressure on the upstream side, it is assumed that the forces acting on the valve element will not balance until the pressure times the effective pressure area on the downstream side (plus the force of the biasing spring) is equal to the pressure times the effective pressure area on the upstream side. Thus, one prior art approach is to minimize this effect by roughening the contact surfaces to discourage full contact of the valve element with the valve seat. However, surface roughening is sometimes a short term solution since the contact forces tend to make the contact surfaces more smooth. Another prior art approach is to minimize the contact area between the valve element and the valve seat. However, this can undesirably increase the local load bearing forces (both static and impact) with a consequent increase in wear. A search of the patent literature has disclosed a number of U.S. patents, these being the following: U.S.4,620,562 (Pacht) shows a pressure regulating valve for a high pressure hydraulic apparatus, such as a water jet cutting and blast cleaning apparatus where the pressure ranges between 10,000 [68947,6 kPa] and 50,000 psi [34473.8 kPa]. Figure 3 of that patent illustrates a valve closure element 36 which has a frusto-conical head portion 38 that in the closed position fits against a matching frusto-conical valve seat surface 64. The pressurized fluid enters through an inlet passageway 54 to act against the piston 40 and move the valve element 36 out of its seating position, with the high pressure fluid surrounding the valve element flowing by the valve element and into the discharge passageway 56. The flow of fluid is from the chamber surrounding the valve element into the passageway which the valve element closes. U.S. 4,596,321 (Harper et al), shows a bi-directional flow control valve for a damping head assembly, this being a fluid filled shock absorber. There is a valve element 64 which under high pressure in the cylinder chamber 38 moves to the right so that a plurality of small radial openings 76 come into registration with the passageway inlet 58a. Thus, the fluid in the chamber 38 under high pressure can pass through the opening 76 and into the passageway 58a to permit the shock absorbing piston to move to the left (i.e. direction "A" as shown in figure 2 of the patent). The reason for the arrangement of these ports 76 is described in column 7 of the patent, beginning on line 29. It is pointed out that if there are relatively large openings in the valve element 64, this valve element 64 will stick and will not open when the pre-load is exceeded. It is alleged that the sticking action of the valve element 64 is due to the flow reaction forces produced in accordance with Bernoulli's Law, in that as the valve element is just cracked open sightly, the deflection of fluid flow as it strikes the edge of the fixed ports 58a and acting on the valve element 64 prevents it from opening. However, these forces are minimized by providing ports 76 which comprise a large number of very small openings through the skirt portion 68. U.S. 4,527,351 (Gerakiteys), discloses a "Levitated Ball Toy" which utilizes Bernoulli's principal to cause a light ball to remain positioned adjacent a tube through which the person blows. There is a cup shaped element at the end of the tube, and as the person blows into the tube, the air flows outwardly from the exit end of the tube and radially outwardly through the small space between the surface of the ball and the cup shaped element, with the reduced pressure in the area between the cup and the ball keeping the ball positioned adjacent to the cup. Patentability is predicated upon a relieved portion of the central port which biases the escaping air in one direction to cause the supported ball to spin. U.S. 4,269,227 (Araki et al) discloses a valve which is adapted to discharge steam. There is a main valve body 42 that fits against a valve seat 40. Additionally, there is an auxiliary valve body 46 which is moveably positioned within the valve body 42. In operation, when the auxiliary valve element 46 is moved away from its seat, and also the main valve element 42 is also moved away form its seat, the steam follows, due to the Coanda Effect, the curved surface of the valve seat 40 to pull toward the outlet, and there is also flow by the auxiliary valve element 46. The effect of this is to remove unstable flow. Also, there is a sharp edge or corner formed at 48 on the main valve body 42 to enable the steam stream running through the main fluid passageway 50 to easily leave the main valve body 42 and flow downwardly through the outlet. U.S. 4,215,715 (Raskin) shows a poppet valve which is used, for example, to discharge pressurized air in a short period of time (e.g. a few seconds). The surface 34 of the poppet valve that defines with the valve seat surface the fluid passageway has a number of different configurations, shown in figures 2,3, and 4. In figure 2, there is a frusto conical outer surface 36a of a greater angle, relative to a transverse plane, and the surface 34 of a shallower angle. In figure 3, the surface portion 366 is curved in a section taken parallel to the longitudinal axis of the poppet valve, and surface section 38b which is also curved and joins to the surface 366. U.S. 3,357,879 (Bennett) shows an arrangement where a pulp material which is to be fed into a paper making machine is passed over a surface having a fish scale like pattern on the valve members to provide a faster and smoother fluid flow. U.S. 3,245,429 (Bacino et al) discloses a poppet valve for use in small high pressure pumps. The periphery of the seal face of the valve element has a packing ring 35. Further, the seal face of the poppet valve has a plurality of radially extending grooves 36. In column 2, beginning on line 37, it is stated that these grooves 36 provide access of fluid between the adjoining seal faces 17 and 33 to prevent a secondary seal from occurring near the bore 18 through which fluid flows toward the valve element. It points out that this will avoid the hammering action which produces noise and damage. U.S. 1,777,611 (Grohek) discloses a check valve where there is a valve element 11 having a frusto conical surface which fits in a valve seat having a matching surface. U.S. 1,665,394 (Willoughby) shows what is called a safety valve, where the matching surfaces of the valve element and the valve seat have non-flat surfaces. SUMMARY OF THE INVENTION The problems experienced with the prior art valves are alleviated by the features of the characterizing part of claim 1. The valve of the present invention comprises a valve seat member having a passage defining surface which defines a valve passageway having a forward outlet end portion. The valve seat member also has a valve seat contact surface which extends radially outwardly from the outlet end of the valve passageway. There is a valve element having a contact surface, with this valve element being moveable between a closed position where the valve element contacting surface bears against the valve seat contact surface to close the valve passageway, and an open position where the valve element contact surface is spaced from the valve seat contact surface to define therebetween a radially outwardly extending passageway region to receive flow from the valve passageway. The passageway defining surface meets the valve seat contact surface at a transition region where flow from the valve passageway flows into said radially extending passageway region. The valve seat member has a recess surface portion which defines at said transition region an annular section having a radially inward rear edge portion, a radially outward forward edge portion, and an intermediate surface portion, said rear edge portion and said forward edge portion defining end limits of a transitional flow surface region, said intermediate surface portion defining an annular fluid recess spaced radially outwardly of said transition fluid flow surface region. Thus, fluid flow from the valve passageway flows through said transition region with the transitional fluid flow surface region defining a flow boundary of said fluid. In one configuration, the intermediate surface portion has a rear generally transverse surface section extending radially outwardly from the passageway defining surface, and a generally longitudinally extending surface section facing radially inwardly toward said valve passageway. The transversely extending surface section forms with the passageway defining surface a relatively sharp circumferential edge which is sufficiently sharp to cause tripping of boundary layer flow adjacent to said circumferential edge. The longitudinally extending surface portion desirably has a diameter which is between about 1.1 to 1.5 times greater than a diameter of said valve passageway immediately adjacent to said transition surface region, and more desirably between about 1.2 to 1.3 times greater. The recess surface portion desirably has a longitudinal dimension which is between about one to five times a lateral width dimension of said recess, and more desirably between about 1.5 to 3 times. In one arrangement of the present invention, the recess surface portion is positioned radially outwardly of a frusto conical plane defined by the radially inward rear edge portion and the radially outward forward edge portion. In another arrangement, the recess surface portion is positioned adjacent to the frusto conical plane defined by said radially inward rear edge portion and said radially outward forward edge portion. In accordance with another aspect of the present invention, the valve has boundary layer tripping means positioned at a location of flow into said transition region arranged to trip boundary layer flow of fluid flowing along said passageway defining surface. In one arrangement, the boundary layer tripping means comprises means defining a circumferential edge at the passageway defining surface having sufficient sharpness to trip the boundary layer. In another arrangement, the boundary layer tripping means comprises protruding means extending radially inwardly from the passageway defining surface. In yet another arrangement, the boundary layer tripping means comprises a surface portion of the passageway defining surface which is sufficiently rough to cause tripping of the boundary layer. In another embodiment of the present invention, the transition region where the flow from the valve passageway flows into the radially outwardly extending passageway region is arranged so that in circumferential cross sectional configuration, it is convexly curved in a continuous curve to cause boundary layer flow along said transition surface in a continuous curved path from said valve passageway to said radially outwardly extending passageway region. In another embodiment there is an expanded passageway region radially outwardly of said forward outlet end and radially inwardly of said valve seat contact surface to alleviate restricted flow from said valve passageway. In a method of the present invention, the flow of the fluid flowing through the valve passageway is tripped at a location rearwardly of the transition region, as described above. Other features of the present invention will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view taken along a longitudinal center line of an outlet portion of a pump incorporating the valve of the present invention; Figure 2 is a somewhat schematic drawing of a typical prior art poppet valve used in a high pressure pump, this view being taken in section along a longitudinal center line of the valve, and illustrating a flow pattern, the recognition of which in the present invention is believed to be at least in part responsible for the solution provided by the present invention; Figure 2A is a graph illustrating pressures generated at the valve element surface during opening of the valve element; Figure 3 is a sectional view taken along the longitudinal axis of the valve of the present invention, drawn to an enlarged scale and illustrating certain aspects of the flow patterns through this valve. Figures 4 through 6 are cross sectional views similar to Figure 3 showing modified versions of the recessed area of the valve seat element of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT It is believed that a clearer understanding of the present invention can be obtained by preceding the description of the present invention with a review of the structure and operation of a high pressure pump in which the present invention can desirably be incorporated. With reference to Figure 1, this pump 10 comprises a cylinder housing 12 defining a high pressure chamber 14, in which reciprocates a high pressure plunger or piston 16. There is an end block 18 fixedly connected to the end of the cylinder housing 12, and containing a valve assembly generally designated 20. This particular valve assembly 20 is the subject matter of a co-pending application, entitled " HIGH PRESSURE PRUMP VALVE ASSEMBLY" which has been filed previously in the U.S. Patent and Trademark Office on April 4, 1989, Serial No.07/333,560. In describing the present invention, the pump apparatus 10 will be considered as having a center longitudinal axis 22 which extends along the reciprocating path of the plunger 16. The term "forward" will denote a direction toward an outlet end of the pump apparatus 10 (which is to the left in Figure 1, while the term "rear" or "rearward" will denote the opposite direction. The term "radially outward" shall denote a direction or location away from the longitudinal center axis 22, while the term "radially inward" will denote proximity to, or a direction toward, the longitudinal axis 22. The valve assembly 20 comprises a valve block 24 which is positioned forwardly of, and aligned with, the plunger 16. This valve block 24 has forward and rear seals 26 and 28 which form seals between the valve block 24 and the end block 16 and the cylinder housing 12, respectively. There is an inlet check valve 30 in the form of a disc 32 which is positioned to close a plurality of inlet openings 34 which are formed in the valve block 24 and which permit water at low pressure to flow into the chamber 14 on the intake stroke of the plunger 16. This disc 32 is retained by a suitable bolt 36 which permits limited movement of the disc valve element 32 between its open and closed position. This inlet check valve element 32 is, or may be, of conventional design. The valve of the present invention is generally designated 38, and this valve 38 functions as a check valve to receive high pressure fluid flow from a center passageway 40 leading from the chamber 14. This passageway 40 has a rear portion 42 formed in the bolt 36 and a middle passageway portion 44 formed in the valve block 24. Before describing in detail the inventive features of this valve 38, we will continue with a brief description of the main components of the pump 10 (including the main components of the valve 38) so that the overall pump configuration in which this valve 38 is incorporated can be properly understood. There is a cylindrically shaped valve guide sleeve 46 having a rear threaded end 48 that screws into the forward end of the valve block 24. Positioned within this valve guide sleeve 46 is a cylindrically shaped valve element 50 which is fixedly mounted to the rear end of a plastic guide member 52 that is mounted for limited back and forth slide movement in the valve guide sleeve 46. A compression spring 54 urges the guide member 52 rearwardly to place the valve element 50 in its closed position. There is a valve seat member 56 which fits within the forward end of the guide sleeve 46. This valve seat member 56 has a cylindrical configuration and has a through center opening 58 which is aligned with and has the same cross-sectional configuration as, the aforementioned passageway 40 so as to essentially form a continuation thereof. The guide sleeve 46, guide member 52 and valve element 50 are positioned in a valve chamber 60 which is defined by the end block 18. There is an outlet passageway 62 leading from the chamber 60 to a manifold, accumulator, or other apparatus to receive the high pressure fluid from the pump 10. As indicated previously, one of the uses of the pump 10 is to supply fluid (e.g. water) to provide a high pressure water jet. Thus the pressure in the valve chamber 60 is maintained at high pressure. A spacing sleeve 64 is positioned within the periphery of the chamber 60 to position the aforementioned forward seal 26. To describe briefly the overall operation of the pump 10, on the intake stroke, the plunger 16 moves rearwardly in the cylinder chamber 14 (i.e., to the right, as shown in Figure 1), so that the inlet valve element 32 moves rearwardly so that fluid flows through the inlet openings 34 and into the chamber 14. At this time, the urging of the compression spring 54 and also the fluid pressure in the valve chamber 60 hold the valve element 50 in its closed position against the valve seat member 56, thus preventing backflow of the high pressure fluid in the valve chamber 60 into the cylinder chamber 14. On the discharge stroke, the plunger 16 moves forwardly (i.e. to the left as seen in Figure 1) to create very high pressure in the cylinder chamber 14 (e.g. 10,000 psi [68947.6 kPa] up to 100,000 psi [689476 kPa] or more). At such time as the force resulting from pressure in the cylinder chamber 14 exceeds by a sufficiently high amount the force resulting from the fluid pressure in the valve chamber 60 and the force of the compression spring 54 against the valve element 50, the valve element 50 moves away from the valve seat member 56 to permit flow of high pressure fluid through the outlet passageway 40 and into the valve chamber 60, from which the fluid flows outwardly through the outlet passage 62. However, as indicated previously herein under the heading "Background Art" one of the problems in prior outlet poppet valves is that there sometimes is a delay in the valve moving to a full open position so as to cause what are sometimes very severe pressure spikes within the cylinder chamber 14. The present invention is based upon the hypothesis or discovery that the so-called "sticking" of the poppet valve is not an accurate explanation of the phenomena involved. Rather, it is hypothesized that the delay in the valve element moving to its full open position is due to a condition of an area of low pressure between the contact surfaces of the valve seat and the valve element, where low pressure is developed during the initial opening phase as the valve element moves away from the valve seat in a manner to tend to move the valve element back toward its closed position. This will be explained further with reference to Figures 2 and 3. In Figure 2 there is shown a typical prior art poppet valve 70 comprising a cylindrically shaped poppet element 72 and a valve seat element 74 having an upstream through passageway 76 with an outlet end portion 78. The valve seat element 74 thus defines an annular planar contact surface area 80 which extends radially outwardly from the passageway outlet portion 78 and is arranged to come into contact with a matching contact surface 82 formed on the poppet element 72. As indicated previously, one of the prior art approaches in solving the so-called "sticking" problems is predicated on the theory that the effective pressure surface area on the downstream pressure surface 84 on the back side of the poppet element 72 is greater than the effective pressure surface area 86 which is exposed directly to pressure from fluid in the upstream passageway 76 when the poppet element 72 is in its fully closed position. Thus, it is surmised that it is necessary for the pressure in the passageway 76 to rise to a sufficiently high level so that the force to open the poppet valve (computed by multiplying the cross-sectional area of the passageway 76 times the pressure in the passageway 76) is just greater than the force of the downstream pressure closing the poppet valve (this being computed by multiplying the total effective pressure area of the surface 84 times the downstream pressure) plus the force of the biasing spring. As indicated above, in accordance with the hypothesis of the present invention, this is believed to be an inadequate explanation. With further reference to Figure 2, in accordance with the hypothesis of the present invention, when the pressure in the upstream passageway 76 begins to exceed the pressure downstream of the poppet element 72, with the poppet element 72 fully closed, the fluid pressure from the passageway 76 radiates outwardly between the contact surfaces 80 and 82 rather rapidly so that there is sufficient pressure not only against the central surface portion 86 of the poppet element surface 82 but also against the annular contact surface 82 of the poppet element 72 to cause the poppet element 72 to lift away from the contact surface 80 of the valve seat element 74. Then, in accordance with the hypothesis of the present invention, another phenomenon occurs. The flow which is more closely adjacent to the surface 88 defining the passageway 76 (this flow line being indicated at 90) moves around a circumferential edge or corner 92 to flow into the radially expanding passageway area 94 which is between the surface areas 80 and 82 and which extends outwardly from the outlet end 78 of the passageway 76. In doing so, this portion 90 of the fluid flow tends to separate after it passes by the edge 90 to form an annular area of separated flow indicated at 96. This annular area 96 creates a reduced pressure area which causes a substantial pressure reduction in that portion of the valve element contact surface 82 which is immediately adjacent to this annular turbulent area 96. It is surmised that this results from the separated flow areas 96 effectively forming a restricted passageway area 97 between the surface area 82 and the turbulent area 96 where velocity increases to cause a lower static pressure. To proceed further with an explanation of the hypothesized flow pattern and its effect, reference is now made to Figure 2A where the base line represents the pressure at the surface areas 82 and 88. Let it be assumed that the poppet element 72 is fully closed so that the contact surface 82 is bearing against the valve seat contact surface 80. As the associated piston begins its pressure stroke, pressure in the passageway 76 builds up, with this pressure migrating outwardly between the contact surfaces 80 and 82 so that the total pressure on the central contact area 86 and the annular contact area 82 of the poppet element 72 is sufficient to cause the poppet element 72 to initiate lifting off the valve seat 74. Coincidentially, the fluid flows at high velocity through the passageway 76, around the circular edge 92 and into the radially expanding passageway 94 which is defined by the closely adjacent contact surfaces 80 and 82. It is at this time that the annular separated flow area 96 is formed, and at this time it will have significant dimensions relative to the small opening dimension, causing very high velocity flow adjacent to the separated flow area 96 to cause the low pressure area indicated at 98 in Figure 2A. This low pressure area causes a pressure imbalance so that pressure against the front valve element surface 84 actually tends to move the poppet element 72 back toward its closed position, thus pausing in this position and further restricting flow outwardly through the radially expanding passageway 94 and causing a pressure spike within the passageway 76. This pressure spike in the passageway 76 continues to build up to a level indicated at 100 until the force against the upstream side of the poppet element 72 at the surface area 86 is sufficient to move the poppet element 72 further from the valve seat 74 and permit adequate flow to alleviate the pressure spike which will drop from the level shown at 100. It is to be understood that with the very high fluid pressures, the fluid compressibility and the high fluid velocities involved, it is very difficult to get direct measurement and observation within the flow area of the valve. The hypothesis described above was derived by examining data relating to fluid flow and pressures during the operation of the valve 72 of Figure 2 moving toward its open position. A computer model was made to simulate these pressures and presumed flow conditions and from this the hypothesis of the present invention was derived. However, it is to be understood that regardless of the accuracy of the above described hypothesis in accounting for the improved performance of the present invention, it has been found that by incorporating the teachings of the present invention, the so-called "sticking" phenomenon of the valve has been alleviated to a substantial extent. With the foregoing in mind, reference is made to Figure 3 which illustrates the valve of the present invention, drawn to an enlarged scale relative to Figure 1. There is shown in Figure 3 she valve 38 comprising the aforementioned valve element 50, which has a cylindrical configuration, and the valve seat member 56 defining the passageway portion 58. The center axis of the valve 38 is indicated at 110. The downstream end portion of the cylindrical surface 112 that defines the passageway portion 58 is formed with an annular recess 114 which in peripheral cross-sectional configuration has a right angle annular profile, which can be considered as a right angle cutout. More specifically, there is a radially outwardly extending forwardly facing annular surface 116 which forms with the cylindrical surface 112 a circumferential edge or corner 118. Also, there is a radially inwardly facing cylindrical surface 120 which is stepped radially outwardly from the passageway defining surface 112. This cylindrical surface 120 forms with a radially outwardly positioned contact surface 122 of the valve seat member 56 a second circumferential edge or corner portion 124. The valve element 50 has a cylindrical configuration. To describe the hypothesized mode of operation of the valve 38 of the present invention, let it be assumed that the valve element 50 is in its closed position so that its annular contact surface 126 bears against the contact surface 122 of the valve seat member 56. As the valve element 50 moves just a short distance forwardly from its closed position, a radially expanding annular passageway 128 is formed between the contact surfaces 122 and 126. As fluid begins to flow forwardly through the passageway 58, the fluid closely adjacent to the passageway defining surface 112 passes closely adjacent to the circumferential edge or corner 118 formed by the surface portion 116 and the surface 112. It is believed that this circumferential edge 118 trips the fluid flow immediately adjacent to the edge 118 so that there is a separated flow area 130 within the annular recess 114. It is surmised that there may be a rotational pattern of flow about a circumferential axis of the recess 114. It is further surmised that this annular separated flow area 130 has the effect of defining an area of relatively static fluid pressure that in effect provides a boundary surface area indicated schematically by a broken line indicated at 132 on the right side of Figure 3. It is further surmised that this effective boundary area 132 has in peripheral cross-sectional configuration a convexly curved configuration which provides for a smooth transition of the fluid flow from the passageway 56 around the curved surface area 132 and thence through the annular radially expanding passageway area 128. It is believed that this gradual guidance of the flow helps to alleviate the formation of the separated flow area 96 described above with reference to Figure 2. In addition to the proposed phenomenon described immediately above, it is believed that another flow phenomenon is taking place. It is known that when there is fluid flow through a passageway, there is the boundary layer effect, where the fluid immediately adjacent to the passageway surface is slower, and the rate of fluid flow increases in the boundary layer region in a direction toward the center of the passageway. Thus, there is a velocity gradient beginning close to zero immediately adjacent to the passageway surface and increasing radially inwardly. There is a tendency for this boundary layer to become thicker in a downstream direction so that there is an increasing amount of lower energy boundary layer fluid. With further reference to Figure 3, it can be hypothesized that as the fluid flow closely adjacent to the surface 112 passes the edge 118, this has the effect of "tripping" the boundary layer so that the higher energy fluid in the main part of the passageway rotates inwardly more closely to the boundary layer, and the lower energy boundary layer fluid moves into the mainstream of the fluid flow. This has the effect of energizing the boundary layer so that it is less likely to separate. Thus, when the fluid flow reaches the location of the edge 124, this higher energy fluid which moves closely adjacent to the edge 124 is less likely to separate, thus alleviating the tendency to form the separated region 96 described with reference to Figure 2. To describe another facet of the preferred embodiment of the present invention shown in Figure 3, it is to be recognized that with the very high pressure in the downstream valve chamber 60, on the intake stroke of the piston 16, there can be very high impact and static pressures exerted by the valve element 50 coming into contact with the valve seat member 56. This can be analogized to a "hammering" action, and it can result in deformation of the valve seat member 56 in the area of the corner 124. This can have the effect of eventually moving some of the material at the location of the corner 124 radially inwardly which could cause a further disturbance of the flow in that area. It has been found that with the embodiment of Figure 3, even though this deformation can occur, the presumed problem of the undesired flow separation at the area 96 (see Figure 2) is still alleviated. In a typical preferred arrangement of the embodiment of Figure 3, the diameter of the passageway 58 (indicated at "a" in Figure 3) is 0.22 inch [0.56 cm], and the diameter of the cylindrical surface 120 (indicated at "b" in Figure 3) is 0.27 inch [0.68 cm]. The lengthwise dimension "c" of the surface 120 is about 0.05 inch [0.127 cm]. The diameter of the valve element 50 (indicated at "d") is about 0.42 inch.[1.07 cm] The total movement of the valve element 50 from its closed position to its open position would be between about 0.03 to 0.07 inch [0.08 cm to 0.18 cm]. It is believed that the diameter of the recess (indicated at "b" in Figure 3) would be between about 1.1 to 1.5 times the diameter of the passageway 58 (indicated at "a"), desirably between about 1.2 to 1.3 times, and more desirably between 1.2 to 1.25 times. The longitudinal dimension of the recess defining surface section 132 (indicated at "c" in Figure 3) is desirably between about 1 to 5 times the lateral thickness dimension of the recess 14 (indicated at "e" in Figure 3), and more preferably between about 1.5 to 3 times. The longitudinal dimension of the recessed defining surface section 132 (indicated at "c") Figure 3 is desirably between about 0.15 to 0.3 times the diameter of the passageway 58 (indicated at "a"), and more preferably bewteen about 0.2 to 0.25 times. It is has been found that the preferred embodiment of the present invention illustrated in Figure 3 is a significant advance in alleviating the valve delay opening problem. To speculate on possibly broader aspects of the present invention, on the assumption that the hypothesis on which the present invention is based has at least some measure of validity, alternative embodiments could also be feasible. Figures through 6 show other possible arrangements of the embodiment of the invention shown in Figure 3, with these showing variations in the configuration of the recess 114. In Figure 4 , the cylindrical surface 120d is longitudinally aligned, while the angular surface 116d slants in the configuration of a frusto conical surface. In Figure 5, the two recess defining surface portions 116e and 120e are at the same slant so that these in effect form a single frusto conical surface to define the recess 114e which in effect is in circumferential cross section triangularly shaped. In Figure 6, the recess 114f is formed with the surface portion 116f meeting the surface portion 120f in a continuous curve. Also, it is to be understood that the contact surfaces 122 and 126 could have configurations other than planar configurations. For example, these could possibly be slanted so as to extend radially outwardly in a frusto conical configuration. Or these could be made as matching convex and concave surfaces.

Claims: A very high pressure liquid pump (10) arranged to alleviate delayed outlet valve opening in a manner to prevent pressure spikes at initiation of an outflow portion of a pumping cycle, said pump comprising: a. a structure defining a liquid chamber (14) to receive liquid which is to be pumped; b. piston means (16) arranged to pump liquid from said chamber (14) at a very high pressure; c. an outlet valve comprising: i. a valve seat member (56) having: 1. a passageway (40) defining surface which defines a valve passageway having a forward outlet end portion; 2. a valve seat contact surface (122) which extends radially outwardly from the outlet end portion of the valve passageway (40); ii. a valve element (50) having a valve element contact surface (126) said valve element being movable between a closed position where said valve element contact surface (126) bears against said valve seat contact surface (122) to close said valve passageway (40) and an open position where said valve element contact surface is spaced from said valve seat contact surface to define therebetween a radially outwardly extending passageway (128) region to receive flow from said valve passageway; iii. said passageway defining surface meeting said valve seat contact surface at a transition region where flow from said valve passageway flows into said radially outwardly extending passageway region (128), said valve seat member having a recessed portion which defines at said transition region an annular recess (114) having a radially inward rear edge, a radially outward forward edge and an intermediate surface, said rear edge and said forward edge defining end limits of a transitional fluid flow region, said intermediate surface being between the rear edge and the forward edge of the annular recess (114) and these two edges also define the end limits of the transitional flow region, characterized in that the valve element contact surface (126) extends to the radially outer edge of the valve element (50) and as said piston means (16) begins a discharge stroke, so as to move said valve element (50) away from said valve seat member (122) potential pressure reduction adjacent to said transition region is substantially alleviated to permit said valve element to move to a fully open position without creating any substantial pressure spike in said chamber. The pump as recited in claim 1, wherein said intermediate surface portion has a rear generally transverse surface section extending radially outward from said passageway defining surface, and a generally longitudinally extending surface section forcing radially inwardly toward said valve passageway. The pump as recited in claim 2, wherein said transverse surface section forms with said passageway defining surface a relatively sharp circumferential edge which is sufficiently sharp to cause tripping of boundary layer flow adjacent to said circumferential edge. The pump as receited in claim 3, wherein said passageway (58) defining surface has a diameter (120) at a location rearwardly of said recess surface portions which is between about 1.1 to 1.5 times greater than a diameter of said valve passageway immediately adjacent to said transition surface region. The pump as recited in claim 4, wherein said recess surface portion (132) has a longitudinal dimension which is between about 1 to 5 times a lateral width dimension of said recess. The pump as recited in claim 3, wherein said passageway defining surface portion has a diameter at said location rearwardly of said recess surface portion which is between about 1.2 to 1.3 times greater than a diameter of said valve passageway immediately adjacent to said transition surface region. The pump as recited in claim 6, wherein said recess surface portion has a longitudinal dimension which is between about 1.5 to 3 times the lateral width dimension of said recess.

Inventors: TAN DAVID K M, TAN, DAVID K.M.
Applicants: FLOW INT CORP, FLOW INTERNATIONAL CORPORATION
Application year: 1990
Main classification: F04B53
IPC codes: F04B53, F16K17