US3050038A - Valve mechanism for fluid operated downwell pumps - Google Patents

Description

P. S. BLOUDOFF Aug. 21, 1962 VALVE MECHANISM FOR FLUID OPERATED DOWNWELL PUMPS Filed Fabi' 21, 1961 2 Sheets-SheetI l MNH..

PETER S. BLOUDOFF ATTORNEYS Aug. 21, 1962 P. S. BLOUDOFF VALVE MECHANISYM FOR FLUID OPERATED DOWNWELL PUMPS 2 Sheets-Sheet 2 Filed Feb. 2l, 1961 ATTORNEYS LOWER PIS TON FACE "w" United States Patent i 3,050,038 VALVE MECHANISM FR FLUID OPERATED DOWNWELL PUMPS Peter S. Bloudoi, 16726 Sausalito Drive, Whittier, Calif. Filed Feb. 21, 1961, Ser. No. 90,841 4 Claims. (Cl. 121-123) This invention relates to iiuid operated downwell pumps and is particularly directed to the valve mechanism for the operating engine of such a pump.

In general, a `fluid operated downwell pump as used for `deep oil wells, for example, includes superimposed but separate engine `and pump cylinders and a reciprocating engine piston to which ya pump piston is attached, the pump piston operating in its own cylinder either as la -double-acting or a single-acting device. The operating Iliuid for the engine is usually clean crude oil conveyed from the surface under very high pressure either in a separate tubing string or in the suitably packed well tubing in which 4the pump and engine cylinders are set. The pump can, yas is known in the art, be operated as a free pump in which case it `can be pumped out through the well tubing, or as a iixed pump in which case power oil may be supplied through `a separate macaroni string within the well tubing. Production fluid discharged by the pump is taken to the surface through a separate discharge conduit :at exhaust or `discharge pressure. The spent power oil, after being used for actuation of the engine piston, may be intermingled with the pump discharge or may be returned to the surface separately. All of these various combinations of tubings and conduits yare well known in the art.

ln many of the pumping devices known in the art the engine piston is of the dierential area type in which power oil at high pressure appears constantly below the engine piston while valve means are prvided to connect the'top portion of the engine cylinder above the piston alternately to a `discharge conduit and to the source of power oil. Since the effective yarea of the top of the engine piston is larger than the effective area of its lower face because of the presence of the connecting rod between the engine and pump pistons, the engine piston will move downwardly if the pressure on its upper face is approximately the full power oil pressure. IIn Ithe pump of the present invention, the pressure is slightly diminished during the down stroke, but the existing pressure times the area of the top of the piston is still greatly in excess of the product of the power oil pressure and the area of the lower piston face. Thus a large force is available to cause -a down stroke of the pumpA piston. The upstroke of the engine piston is caused lby the difference in pressures on the two faces of the engine piston, the lower face being at high pressure and the upper face being at exhaust pressure.

I-t is also known in the art that the valve which controls the ow of power oil into the top of the engine cylinder and which causes this space to be connected to discharge can be carried within the engine piston itself. There are many advantages derived from this disposition of the parts, 'all of which have been recognized and fully explained in Patent 2,921,531, issued January 19, 1960, for the invention of John R. Brennan and Peter S. Bloudoff, entitled Pressure Fluid Operated Pump Structure. Since the valve is disposed within the reciprocating piston, it can test be operated hydraulically. To this end, ithas been proposed in the above patent and in the patents to Roy H. Deitrickson Nos. 2,966,893; 2,966,894 and 2,966,- 895, to provide the valve body section of the engine piston with passages which will subject a differential `area portion of the valve to high pressure at one end of the stroke and in this manner cause reversal of the valve. The op- 3,050,038 Patented Aug. :21, 1962 rice 2 posite reversal can be brought about either by a decided change in pressure on one or more surfaces of the valve or by causing a biasing force which has -been acting on lthe valve body to diminish or disappear.

Valve mechanisms are known in which a pressure differential acting on equal Iareas of the valve body causes the valve to remain in an attained operative position.

The force resulting from the pressure differential acts as a biasing force overcoming a smaller force which tends always to shift the valve body to its opposite position. Thus, if and when the pressure differential disappears, which event usually occurs at the end of the stroke of the engine piston in one direction, the valve will move to its opposite operative position. One of the recognized meth-4 ods of inducing a usable pressure dierential is to cause a flow of engine operating fluid over an enlarged portion of the valve body so that the flowing fluid can expand to a reduced' pressure in the space at the downstream side of the enlarged valve portion. Another recognized method of inducing such a pressure differential is to cause the high pressure power oil to flow through a restricted port or passage so that the pressure on the downstream side of the port or passage is less than the pressure on the upstream side thereof.

In the prior patent to Brennan and Bloudotf, abovementioned, the valve or valve spool is maintained in its operative position Iduring the down stroke by reason of the existence of a higher pressure on the lower side of a valve collar than on the upper side, the spool being biased `downwardly against this force. In that patent the restniction which causes the drop in pressure above the valve collar is caused by choking off the lflow through a port entering a restricted passage for power oil which thus flows through both radial and axial passages drilled in the valve collar itself.

In the present invention the pressure differential needed to act on the valve body is brought about by flowing the hydraulic fluid at high pressure into a charnlber delined on one side by a tightly tting, solid valve collar, flowing the fluid out of the chamber into an annular space formed by a reduced diameter portion of the piston through .a peripheral lseries of ports and reintroducing the fluid `into the space on the opposite or upper side of the solid coll-ar. The constantly operating force which is counteracted by theA aforementioned biasing pressure differential acts in la direction tending to close the first peripheral series of ports and thereby to choke olf the flow of high pressure oil out into the annular space from beneath the collar. As thejllow is progressively restricted by movement of the collar over the ports, the pressure above the collar is progressively reduced and the pressure -beneath the collar then predominates to the point that the Iforce urging the valve body to reverse is balanced out. When the pressures above and below the collar are equalized, either by reducing the pressure on the lower side or increasing the pressure on the upper side the pressure While the operation yof the valve spool is very similar` to that shown Iand described in the Brennan and Bloudoff Patent V2,921,531, the spool itself is greatly simplified mechanically andthe time required to machineit is greatly 3 reduced. The cost of the downwell pump can likewise be reduced and its use correspondingly extended.

The solid collar valve spool and the new disposition of the power oil ports employed in the present invention also lead to a faster reversal of the valve in response to the forces tending to switch it from one position to the other. In the valve of the prior patent, it was necessary for the spool to pass over a plurality of axially spaced ports in its traverse from one position to the other. In the present invention, the spool effectively passes over only one peripheral series 'of ports in moving from its down stroke to its upstroke position.

The port arrangement utilized in the present invention also assures that there is never a quiescent body of oil standing in a chamber on either side of the valve spool collar, and that the entire flow path of the power oil is purged at each down stroke of the engine piston. Thus, any solid particles which might be entrained in the power oil cannot settle out into areas that have no substantial iiow to cause sluggish movement and possible seizure of the valve spool.

Since the areas over which the valve spool must be closely tted in its sleeve are reduced in the present invention, 4it becomes possi-ble deliberately to open up the space around the spool during shifting and thus greatly increase the speed of switching at the top reversal as will become apparent hereinafter. p Y

The primary object of the present invention is to provide a valving system for a iiuid operated downwell pump which is less expensive to manufacture and which has improved operating characteristics as outlined above.

Other objects and advantages of the invention will become apparent from the following detailed description of a preferred embodiment, reference being had to the accompanying drawings, in which:

FIGURE l is a central -vertical sectional view with parts broken away of a hydraulic motor having a valve mechanism constructed in accordance with the present invention, provision for attachment to the associated pump structure being indicated;

FIG. 2 is a central vertical sectional View, on a somewhat larger scale, of the valve mechanism alone, the valve spool standing in the position that it assumes during the upstroke of the pistons;

' FIG. 3 isa view similar to FIG. 2 with the valve spool standing in the position that it assumes during the down stroke ot' the pistons;

. FIG. 4 is a view similar to FIGS. 2 and 3 with the valve spool standing in the position that it assumes immediately after the reversal at the top stroke of the pistons; and

FIG. S is a fragmentary sectional view through the engine and pump cylinders with the'engine piston shown in elevation and in the position of bottom reversal, or at the extreme elower end of its normal stroke.

The drawings show the outer casing of the downwell pump unit lat 10, this casing being divided by an intermediate packer 12 into an upper engine section 14 and a lower pump section 16 which is broken away except for its'extreme upper end. Power oil from the surface is" introduced into the engine section from a fitting having a central passage18 which may be :threaded into a conventional swasb nose section in the case of a free pump or may receive a macaroni string in the case of a fixed pump as is well known in the art.

An engine cylinder, 2) is carried within the engine casing section 14/and the annular space 22 between the cylinder and casing receives power oil from the passage 18 and thus forms a power oil supply passage for the hydraulic engine.

An engine piston 24 is carried for reciprocation within the engine cylinder and is connected by a polish rod 26 to the pump piston (not shown) by a threaded connection 28, the rod 26 extending through the packer 12 in the usual manner. The space 29 below the packer 12 is constantly at discharge pressure and in communication with the surface through passages that are not shown. This space is used, therefore, to accept spent power oil which ows from the engine in a discharge passage 30 through the hollow rod 26. Y

The engine cylinder 20 is formed with a peripheral series `o power oil supply ports 32 at its lower end, which open from the power oil annulus 22 into the space beneath the engine piston. The lower piston face is, therefore, constantly subjected to power oilpressure.

The space in the engine cylinder 20 above the engine piston is designated 34 in the drawings and, as is Well known in the art, this space is alternately lled with power oil and connected to discharge, and these pressure iiuctuations cause the engine piston to reciprocate. When the pressure in space 34 is nearly equal to the full power oil pressure the piston will make a down stroke because the eiective area of the top of the piston is greater than the effective area of the bottom due to the presence of the rod 26, the lower end of which is subject only :to discharge or static pressure. when `space 34 is connected to discharge pressure, and is caused by the predominance of pressure on the lower face of the'piston.

The engine piston 24 ts closely in its cylinder 20 throughout a major portion of its length, but in the present instance is relieved intermediate its ends opposite the valve mechanism to be 4described so that an annular chamber 3S is formed which is a part lof the path of power oil ow.

The valve mechanism of the present invention is carried within the piston and includes a reciprocating spool 36 having a continuous central discharge passage 37 formed therein` The reciprocating spool is formed to provide a land 38 at its upper end to control ow to and from the Y space 34 over the piston, and below this land a reduced portion followed by an imperforate switching or control collar 39. Below the control collar 39 the valve spool includes a diierential area positive reversing portion comprising a larger diameter l40 and a small diameter lower extension 41. The valve spool cooperates with valve body members which may be separate elements for ease of machining, or may be portions Iof the interior of the piston. In either oase, the valve body elements are formed with ports 42 at the top which lead to axial passages 43|V extending upwardly to communicate with the space 34 over the top of the piston 24. These ports 42 are opposite the top land 38 of the valve spool and are opened thereby to receive power oil on the down stroke or to discharge oil from space 34 through the central spool discharge passage 37 on the upstroke. Below the top operating land, and opposite the collar 39, the valve body member (in case the wall of the piston 24) is formed with two spaced series of peripheral ports 44 and 45. The lower series -45 may be considered as ports through which power Oil flows out into the annular space or chamber 35, and the upper series 44 as ports through which power oil reenters the space above the collar 39. This space is designated 46 in the drawings and constitutes a ow chamber through which power oil passes during the down stroke. As will be more fully described hereinafter, the valve collar 39 loperates to pinch ott" the ports 45 during the down stroke to reduce the pressure of the power oil which appears in the annular chamber 35 and in the ow chamber 46.

At the lower end of the `chamber in which the valve collar 39 reciprocates, the valve body is formed with power oil inlet ports 47 which communicate with the interior of the valve body and also connect to the space below the close fitting portion of the piston 24. In the drawing this annular space is indicated at 48. Immediately below this last Is ries of inlet por-ts, the valve body is formed with dash-t relief ports 50 the purpose of which will become appar t hereinafter.

The lower stem portion of the spool valve operates in 5 dilterential area valve body member 52 formed to accommodate the intermediate land formed by the two The upstroke of the piston takes place diiering spool diameters 40 and 41. thus formed in the valve body is utilized as a valve reversing means, as in the prior Patent 2,921,531, above mentioned. Normally, the Ychamber 54 is connected to exhaust pressure .through an axial passage 56 in the rod 26 which yconnects :to radial rod ports 58. Tlhe rod ports '5S are so located that during reciprocation of the pump they normally communicate with the discharge pressure space 29 or face the interior of the packer i12. At the extreme upper end of the stroke of the engine pi-ston, these ports 58 run out above the packer to the position shown in FIG. l and receive power oil from the engine cylinder 20. The power oil pressure thus appears instantly in chamber 514 and causes the valve spool to move upwardly because of the difference in area of the larger and smaller spool diameters 4G and 41 forming the intermediate valveactuating land. This is a preferred means of reversing the valve at the top of the stroke, but is, of course, not the only means for accomplishing this motion.

The valve stands in its upper working position during the down stroke only because of the reduction in the pressure of the oil above the collar 39 caused by the pinching olf of the ports 45. lf the ow through ports 45' and 44 were to be reduced to any great extent, the flow-induced drop in pressure would disappear and the pressure -above the collar would be equal to the pressure below it, and the valve spool would reverse. Thus, if the engine and pump pistons were to stop before reaching the full llower extent of their intended movement, the ilow through ports 4S 'and 44 would drop to zero and a reversal of motion would take place. This is effective in the event of an accumulation of sand in the pump cylinder, for example, and under these conditions, the pump will short stroke until the sand is washed out or the cylinder cleaned.

Any other device for equalizing the pressures Iabove The chamber 54 and below the pump piston will bring about a bottom reversal.

For reversing the valve rapidly at the bottom of the stroke of the piston 24, the engine cylinder 2) is provided with a relieved or undercut section 59, best shown in FIG. 5. When the annular chamber which bridges the upper and lower power oil comes into registry with this undercut section, the pressure reduction effected by the previously pinched-oit ports is eliminated and full power oil pressure appears immediately above the collar 39. The valve spool then moves promptly to its lower position, ready for an upstroke.

The reversnig movement of the valve spool is greatly improved in the present invention by relieving the inside of the valve body between ports 45 from which power oil flows beneath the collar on the down stroke and the power oil inlet ports 47, the relieved area being indicated at 60. It is not essential that the collar 39 lit the valve body in which it operates except in the region betweenA the upper and lower power oil ow ports 44 and 45. During the transition of the valve spool from one operative position to the other it is desirable that oil How-freely around the collar 39, because the rapidity of the valve traverse can be greatly increased. However, since the valve travels rapidly in its reversing or switching movement, it is necessary to provide a dash-pot at each end of the valve stroke to slow it down to avoid hammering the valve body against the stationary parts of the system. At the top of the valve chamber, the dash-pot comprises a protuberance 62 which is of a size which closely fits the interior bore of the valve spool which has been designated as the discharge passage 37. Thus the periphery of the valve enters the space between the upper valve body member designated `31 and the protuberance 62 trapping a small body of oil in this space .and letting the trapped oil out slowly into the discharge passage. At the lower end, the dash-pot action takes place between the collar 39 and the portion of the valve body immediately below the inlet ports 47. Oil trapped by the .collar at this point is forced out through a few restricted dashpot relief ports 50, thus slowing the motion of the valve spool downwardly at the lower end of its travel.

Operation Upstr0ke.-During the upstroke of the pump and engine pistons, the valve spool 39 stands in its lower position. Ports 42 are open to connect the space 34 above the piston to discharge through the central passage 37 in the valve spool, through the hollow polish rod 26 to the 215 above the pump piston via discharge passage 3h. Power oil to force the engine piston upwardly enters from the power oil annulus 22 through the lower series of ports 32. The reversing chamber 54 is at low pressure. This position of the parts is shown in FlG. 2.

Upper eversal.-The upstroke continues until the rod ports S pull out of contact with the packer l2. Power oil from the lower end of the engine cylinder then enters the rod passages 56 through these rod ports, and appears in the reversing chamber 54. The high pressure in this chamber then acts on the differential area between the valve spool diameters 40 and 4l and force the valve spool to switch to its upper position. This position of the parts is shown in FIG. 1. The engine and pump pistons are now ready for the next down stroke. This upper reversal is substantially the same as that shown in the prior Patent 2,921,531.

Down stroke-When the valve spool moves from its lower to its upper position at top reversal, it'travels rapidly to a position beyond the desired stable position and the dashpot formed by protuberance 62 and the hollow interior of the spool is relied upon to slow it down. The extreme upper position of the valve spool is shown in FIG. 4 and the trapped body of oil which slows and ultimately stops the motion of the piston is indicated therein at 79. It will be seen that the collar 39 stands now between the spaced annular series of power oil flow ports 44 and 45 and that the ports 42 are opened to power oil so that the full pressure of this oil appears in space 34 over the engine piston. Therefore, the piston starts downwardly.

Power oil enters from the inlet ports 47, ows through the space beneath the collar 39 and out through ports 45 into the annular space 35 around the reduced piston area and back by way of ports 44 into the flow chamber .above the collar 39. From the llow chamber the oil passes to the top of the engine cylinder as above described. Since there is a ow of oil in `the spaces 'above and below the collar 39 the chamber in which the valve spool reciprocates is purged or cleansed at each down stroke and there is little likelihood of solids settling out of the power oil to interfere with the proper action of the valve.

The down stroke begins, of course, with the reversing chamber 54 filled with oil at high pressure. This high pressure persists until the rod ports 58 move out of `the lower end of the packer 12, at which time the chamber 54 goes to low pressure. The valve spool, which has been held up by the pressure in the reversing chamber now has a bias downwardly, and would reverse itself. However, when the collar 39 pinches off the lower power oil flow ports 45, the pressure of the oil above the collar is reduced by the amount of the pressure drop in the restricted passage thus formed. Thus the force down on the collar will reach a point of balance with the upward force of power oil beneath the collar. This operating position, which continues throughout the down stroke, 1s shown in FIG. 3. lt will be seen from an inspection of the ligure of the drawings that the solid collar 39 lits tightly against its surrounding surfaces and that the oil that is flowing to the top of the engine cylinder to cause the down stroke does not flow past the collar or over any of its contrlling surfaces so that the collar does not tend to become eroded by the rapid passage of oil thereover. The oil .also flows into and out of .the spaces -above and below the solid collar, so that there are no'dead spaces in which foreign matter can accumulate to become later dislodged and which might interfere with the free sliding movement of the valve spool.

It will also be apparent that the solid valve collar, combined with the annular ow chamber is much simpler mechanically than previously known devices accomplishing similar objects. The collar 39 is piloted in its re ciprocation by the spool extensions above and below it and offers a simple and effective means to control the iiow of operating fluid on the downstroke.

Bottom reversal-The engine and pump pistons continue downwardly until some event occurs which will act to impose full power oil pressure on the upper surface of collar 39 which creates a delinite downward force on the valve spool, and eliminates the biasing force which has been holding it up. This happens when the piston enters the lower dash-pot below inlet port 32 'so that its motion is first slowed and then stopped, so that the iiow through the restricted port diminishes and ceases. In accordance with the form of the invention disclosed in the drawings, the cylinder relieved area 59 accomplishes a greatly increased speed of reversal by putting the annular chamber 35, which normally contains power oil at a pressure reduced by the drop resulting from pinching olf ports 45, into direct communication with the full pressure of the oil beneath the piston 24. The increase in pressure forces the valve to switch quickly to its lower position. As 4the valve collar 39 closes oli the lower ports 4S on its reversing movement, there is no longer any reason to maintain a seal or close fit between the collar 39 and the body in which it operates. Therefore, lthe body can be relieved to permit oil to pass reely from one side of the collar to the other, which greatly increases the speed of the reversing movement of the valve spool. The relieved area is indicated at 6i) in FIGS. 2 and 3. Since the valve spool is moved rapidly downward in its reversal, the mo tion must be cushioned at the bottom by the dash-pot `effect of the oil trapped below the power oil inlet ports 47. At ythis point the interior of the valve chamber is again made to have a close-clearance iit with the valve collar 39 and the trapped oil is Imetered out through the dash-pot relief ports S0. The size of the ports with relation to the volume of oil ltrapped beneath the collar will, of course, determine the dash-pot etect.

With ythe valve in its lower position, the space 34 above the engine piston is again open to exhaust through the communication of ports 42 and the discharge passage 37 through the center of the valve spool. The next succeeding upstroke then occurs and the cycle is repeated.

It will be seen that the present invention provides a simple, imperforate control collar for the valve spool operating in a chamber which is free of obstructions and which contains ilowing oil at each reversal of the valve. Further, the present invention provides means to increase the speed at which the reversal can take place in each direction so lthat the tendency of the engine piston Ito dwell at the ends of its stroke is eliminated or substantially reduced.

While the invention has been disclosed in conjunction with a specific form and disposition of the parts, it should be appreciated that numerous modifications and changes can be made therein without departing from the scope of the appended claims.

What I claim is:

1. In a hydraulically actuated downwell pump of the type comprising a hydraulic engine having a reciprocating dillerential area piston actuated by power oil placed under pressure at the surface and in constant operative communication with the smaller of the diierential areas of the piston, and having valve means controlling ports to apply power oil at substantially fully pressure to the larger of the diierential areas in a down stroke position and to connect said larger area to a discharge pressure in an upstroke position, the improvement comprising an elongated tubular valve spool member carried by and reciprocable in said piston and including an imperforate collar member, means to place the lower side of said valve collar member under constant power oil pressure, means forming a tubular valve body member in said piston in cooperative valving relationship with said valve spool member and having first and second spaced series of peripheral ports leading to an exterior annular chamber, a ow chamber above said valve collar and receiving power oil from said annular chamber through said second series of ports when said valve spool member stands in its down stroke position, whereby power oil flows into the space below said valve collar, through said first series of ports into said annular chamber, through said second series of ports into said liow chamber and thence through said valve controlled ports into the space above said piston, and means to cause a reversal of said valve spool from its down stroke position to an upstroke position.

2. In a hydraulically actuated downwell pump of the.

type comprising a hydraulic engine having a reciprocating diierential area piston actuated by power oil placed under pressure at the surface and in constant operative communication with the smaller of the differential areas ofthe piston, and having valve means controlling ports to apply power oil at substantially full pressure to the larger of the diderential areas in ia down stroke position and to connect said larger area to a discharge pressure in an upstroke position, the improvement comprising an elongated tubular valve spool member carried by and reciprocable in said piston and including an imperforaite collar member, means to place the lower side of said valve collar member under constant power oil pressure, means forming a tubular valve body member in said piston in cooperative valving relationship with said valve spool member and having first and second spaced series 4of peripheral .ports leading to an exterior annular chamber, a liow chamber above said valve collar and receiving power oil from said annular chamber through said second series of ports when said valve spool member stands in its down stroke position, whereby power oil flows into the space below said valve collar, through said'iirst series of ports into said annular chamber, through said second series of ports into said liow chamber and. thence through said valve controlled ports into the space above said piston, an intermediate land formed on said valve spool having a downwardly acting differential area urging said valve spool in a direction to cut olf flow through said lirst series of ports whereby said reduced iiow 'causes the pressure in said llow chamber to he correspondingly reduced to a point of balance at which said iirst series of ports is partially closed, and means to equalize the pressure above and below said valve collar to cause a reversal of said valve spool by the force exerted by said diterential area intermediate land.

3. In a hydraulically actuated downwell pump of the ftype comprising a hydraulic engine having a reciprocating diilerential area piston actuated by power oil placed under pressure at the surface and in constant operative communication with the smaller of the diierential areas of lthe piston, and having valve means controlling ports to apply power oil at substantially full pressure to the larger of the differential areas in a down stroke position and to connect said larger area to a discharge pressure in an upstroke position, the improvement comprising an elongated tubular valve spool member carried by and reciprocable in said piston and including an imperforate collar member, means to place the lower side of Said valve collar member under constant power oil pressure, means forming a tubular valve body member in said piston in cooperative valving relationship with said valve collar member and having rst and second spaced series of peripheral ports leading to an exterior annular chamber, a iiow chamber above said valve collar and receiving power oil from said annular chamber through said second series of ports when said valve spool member stands in its down stroke position, whereby power oil flows into the space below said valve collar, through said irst series of ports into said annular chamber, through said second series of ports into said lflow chamber yand thence through said valve controlled ports into the space above said piston, an intermediate land formed on said valve spool having a downwardly acting differential area urging said valve spool in a direction `to cut oi ilow through said rst series of ports whereby said reduced flow causes the pressure in said ow chamber Ito be correspondingly reduced to a point of balance at `which said first series of ports is partially closed, and means operative at the lower end of the stroke of said piston to supply power oil directly to said annular chamber and said -iiow chamber at full pressure .and thereby move said valve spool 15 219661895 to its opposite position.

10 4. The improvement defined -in claim 1, 4and said valve body having a relieved area, larger in diameter than said valve collar below said rst series of annular ports, Whereby oil can ow freely around said collar during the excursion of said valve spool from one operative position to another.

References Cited in the le of this patent UNITED STATES PATENTS 2,921,523 Brennan et a1. Ian. `19, 1960 2,966,893 Dei-trickson Jan. 3, 1961 2,966,894 Dietcks'on Jan. 3, 1961 Deitrickson Jan. 3, 1961

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