US2746391A - Rotary pump - Google Patents

Description

May 22, 1956 J. F. .JAwoRcwsKl ETAL 2,746,391

ROTARY PUMP 6 Sheets-Sheet 1 Original Filed June 28, 1948 INVENTORS JOSEPH F. TA woleowsk/ NORBERT .7A woko ws/r/ May 22, 1956 J. F. JAwoRowsKl ETAL 2,746,391

ROTARY PUMP 6 Sheets-Sheet 2 Original Filed June 28. 1948 rk i May 22, 1956 J. F. JAwoRowsKl Erm. 2,746,391

ROTARY PUMP JOSEPH F- .TAWOE'OWSK/ NORBERT 324 WOOWS/f/ BY f MWI ATTORNEYS May 22, 1956 J. F. JAwORowsKl ETAL 2,?45391 ROTARY PUMP Original` Filed June 28. 1948 6 Sheets-Sheet 4 ATTORNEYS .TOSEPH F- `7A WOO WS/f/ May 22, 1956 J. F. JAwoRowsKl ETAL. 2,746,391

ROTARY PUMP 6 Sheets-Sheet 5 Original Filed June 28, 1948 L l l sf/ s mi@ @n www m oo -o WRR w www- A mm .r A

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May 22, 1956 J. F. JAwoRowsKl ETAL.

ROTARY PUMP 6 Sheets-Sheet 6 Original Filed June 28, 1948 INVENTORS. I l@ 8 rosEPH F. 7A wozeows/n McRae/1er JA woEows/r/ BY www y adam ATTORNEYS United States Patent .$46,391 nora-RY PUMP Joseph F. Jaworowski, Cleveland, and Norbert Jaworowski, Lakewood, Ghio, assignors to VShockey Corporation, Cleveland, Ohio, a corporation of Ghio Original application .lune 28, 11948,'Serial No. 35,618, now Patent No. 2,696,787,`dated December l14, 1954. Divided and this :application Januaryl9, 1953, Serial No. 332,056 i 2 claims. (Cl. 'ros-42) VThis invention .relates -to an improved high pressure, high output, rotary pump which `is particularly adapted for pumping liquids such as `oil or the like through pipe lines, and for otherheavy duty pumping applications.

One of the objects of the invention is the provision of a looking at the end opposite the drive shaft end.

Figure 2 `is aside elevation of the pump assembly shown vin Figure 1.

Figure 3 is a vertical cross-sectional, view ofour irn- ,proved pump taken substantially on line 3&3 of Figures l and 4. i

Figure 4 is a transverse vertical cross-sectional View taken substantially on line v44l of Figure 2.

Figure .5 is a horizontal cross-se`ctional view taken substantially on line 5 5 of Figure 2.

Figure 6 is a vertical cross-sectional view taken substantially on line 6 6 of Figure and illustrating the automatic stuingbox pressure relief or bleeding arrangement.

` Figure 7 is a fragmentary cross-sectional view, taken substantially on line 7-7 of `Figure 6, and illustrating the rotor drive shaft, `the main shaft bearing and their associated parts.

Figure 8 is Aa vertical cross-sectional view taken substantially on line 8-8 Iof Figure 2 and illustrating the automatic control means whereby pressure -is maintained against the rotor vanes regardless of the direction ofrotation of thepump.

Figure 9 is a detached end elevation of the pump rotor.

Figure 10 is a vertical cross-sectional view taken substantially on line 10-10 of Figure 9.

includes a main housing H, an vend cover and sub-housing P for the vane pressure control mechanism, and an `end cover and drive shaft bearing, housing' B. As is A'clearly seen in Figures 3 and 4 the lhousing H is provided with a central cylindrical bore 1, the `left-.hande'nd of `which (Figure '3) is closed by the end Cover P and the rightfh'and end of which is` closed .by the end cover B. Suitable screws 2 are employed to secure the end covers P and B .to the main housing H. Supported within the cylindrical vbore 1 is a sleeve S which is restrained against 'rotation within. the ,housing Hby any suitable means and is provided with an interior pump vcylinder or `cha'rnb'er'3 of generally oval cross section as 'seen in Figure 4, 'the' horizontal dimension of this pump chamber .3 in the sleeve 'S being greater than its vertical dimension. l

In order to permit `the passage otfluid into and out of ends of the varies 3 2 aiespp'orted and guided thereby.

sientes Mayzz, ,195e

2 the pump chamber 3 the vsleeve S is provided with four circumferentially spaced sets of radially extending slots 4, 5, 6, and 7. Each set, as seen in Figure 5, consists of live axially spaced slots and it will be understoodthat these fluid passages through the wall of the sleeve S may,

if desired, be made-in the form of `a series of drilled holes` or any other suitable "shape. i

The main housing -H is provided with fluid passages to convey the fluid being pumped to and from the ports 4, 5, 6, and 7. In describing these passages it will be assumed vthat the pump rotor is operating in the direction of the arrows on the drawingsto draw iluid inthrough the right-hand (Figure 4) openingS and discharge same through the left-hand opening 9. Accordingly opening (8 will be referred to as the pump inlet and opening 9 as the pump discharge outlet but it will appear later that, when the rotation of the rotor R is reversed, the opening 9 will become the inlet and the opening 8 the outlet Fluid which enters through the inlet 8 is divided at the projection 10 on housing H and a part passes upwardly through the curved passage 11 to the transversely extending headerv chamber 12 which overlies and `connects to the radial ports 4 in the sleeve S (see Figure 4). Another part of the entering fluid passes downwardly through the lower inlet passage 13 which, as is clearly seen in Figure 5,

extends across the full width of the sleeve S and co11- nects to the radial ports 6 in sleeve S. An upper discharge passage 14 in the housing H, similar in form and disposed in side-by-side offset relation to passage 11, extends from the transverse header chamber 15, which over-lies and is connected to the radial discharge ports 7, to the discharge opening 9. lower outlet passage 1`6, similar in form to passage 13, connects the radial discharge ports 5 in sleeve S to discharge opening 9 and the projection 1'7 on housing JH is similar in arrangement and function to projection 10 previously referred to.

Rotor shaft supporting bushings or bearings 18 and i9 are mounted in the end cover members B and P respectively and 'are held against rotation by suitable pins 20 `and 21 (see Figure 5). Thesebushings 18 and 19 have inner flange portions 18 and -19' which are contoured as indicated in Figure 4 to correspond to the cross-sectional I a running iit is provided between the rotor and the wall s of the ehai'nber 3 atfthe nai'rowest dimension of the chamber (top and bottom thereof `as seen in the drawings). The drive shaft D extends through the bushing 18 into the bo're 22 of rotor R and is keyed thereto by suitable keys 28 and 29 (see Figure 3) which are supported `in a novel manner which willbe described later. Shaft D terminates at the center chamber 2 5 of the rotor R and a hollow tubular supporting shaft 30 is secured in the bore 20 of the rotor R'and extends from the opposite side of chamber 2'5 outwardly through bearing bushing 19 and connects to a vane pressure chamber 31, in the end housing P. As is best vseenin Figures 4 .and 5, vanes 32 are `disposed in each of the slots 27 of rotor R. These vanes of their outer end portions extend into the recesses 23 and' 24 at the ends o f rotor R. As the vane guideorcam portions 18 and 19 of bushings 1S and 19 extend respectively into the if'c'esses 23 and 24 of rotor R the outer As these ranges 1s" aan iii ar entur'ed t correspbnd to the cross-sectional form ofthe pump chamber 3 they serve to maintain ythe outer edges of the vanes 32 at all times in close proximity to the wall of the pump chamber 3. The franges 18 and 19 however are not depended upon to maintain sealing contact between the edges of the vanes and the pump chamber as fluid pressure means, to be described in detail later, is provided for urging the vanes into proper sealing contact with the wall of the 'pump chamber.

`The outer end portion of drive shaft D may be mounted in an anti-friction bearing 33 and a stuffing box or oil Vseal of any suitable type is generally indicated at 34 and is provided to prevent leakage around the shaft to the outside of the housing. A lubricant retaining seal for the antifriction bearing 33 is shown at 3S in Figure 3 and the projecting end of shaft D may be keyed at 36 for connection to any suitable source of power.

Before describing the other features of our invention an explanation will be given of the operation of the structure described above to pump a uid. Assuming that the rotor R is being driven in counterclockwise direction as seen in Figure 4 and that a supply of uid to be pumped is connected to the inlet opening 8, as the rotor R rotates the vanes 32 will sweep over the inner surface of the pump chamber 3 with their outer edges in engagement therewith and the fluid being pumped will pass from opening 3 through the passages 11 and 13 to the inlet ports 4 and 6 respectively in the sleeve S. Fluid will enter the crescent shaped pumping chamber 37 between the left-hand (Figure 4) side of sleeve S and rotor R through ports 4 and will be picked up by `the vanes 32 and discharged through the ports 5 into the outlet passage i6 und out through opening 9. In like manner a portion of the fluid entering through opening 8 will pass through the lower inlet passage 13 to the inlet ports 6 and into the crescent shaped chamber 38 between the right-hand (Figure 4) side of sleeve S and rotor R. This fluid will be picked up by the vanes 32 and carried to and forced out through the outlet ports 7 into the header 15 and outlet passage 14 and out through the discharge opening 9.

By providing diametrically opposed sets of radially extending inlet ports 4 and 6 and radially extending outlet ports 5 and 7 the pressures on the rotor R are balanced, the bearing loads are reduced, and severe stressing of the parts is avoided thus prolonging the life of the pump. Gurnovel arrangement of inlet and outlet ports and passages provides unrestricted iluid inflow and outflow paths through the pump which paths are of ample cross sectional throughouttheir lengths and free from abrupt bends or sharp corners and thus offer minimum flow resistance with resulting increase in pump eiliciency.

l Our arrangement permits an exceedingly compact and As noted above, the vanes 32 are held in sealing con' tact with the bore of the pump chamber or cylinder a by means of the discharge pressure of the fluid being pumped. This uid pressure is applied through the hollow shaft 30, the center chamber of rotor R, and the holes 26 into which the inner edges of the vanes 32 project (see Figures 3, 4, and l0). As the end faces of rotor R have a running t with the adjacent end faces of cover housings P and B, the oil or other fluid being rpumped which enters the holes 26 can only escape by leaking past the ends of the rotor R or through the bushings 18 and 19. A slight leakage at these points is not 4 objectionable as it serves to maintain a positive lubrication of the relatively moving parts.

Fluid under pressure is supplied to the hollow shaft 30 from the vane pressure chamber 31 (see Figures 3 and 5). This chamber 31, as is best seen in Figures 4 and 8, is connected to the pump chamber 3 through axially extending spaced ports 39 and 40. Port 39 extends from pressure chamber 31 and enters the crescent `shaped chamber 37 on the left-hand (Figure 8) side of the bottom point of engagement of the rotor R with the pump chamber 3. ln like manner port 40 extends from chamber 31 and enters the crescent shaped chamber 38 on the righthand (Figure 8) side of ithe lower Contact point between the rotor R and the pump chamber 3. Thus, when the impeller is rotating in the direction indicated by the arrows in Figures 4 and 8, iluid under high pump discharge pressure will be forced out through port 39 into the pressure chamber 31 and through `the hollow shaft 3i), chamber 25, and holes 26 in rotor R to the undersides of the vanes 32, forcing them outwardly into effective sealing engagement with the wall of the pump chamber 3.

As is best seen in Figures 5 and 8 vertical passages 39 and 49' extend from ports 39 and 40 respectively upwardly and connect to transverse bores 39" and 48 respectively. A central web 41 extends into the pressure chamber 31 and is provided with a bore 42 of the same size as, and concentrically arranged with, bores 39" and 48".

In order automatically to insure a supply of fluid under pressure in the vane pressure chamber 31, regardless of the direction of rotation of the rotor R, a piston or plunger type valve 43 is mounted for reciprocating movement in the bores 39", 40", and 42. This plunger valve 43 is of such length that it is at all times partially disposed in the bore 42 of web 41 and is longer than the distance between the inner ends of bores 39" and 46" to prevent the possibility of communication between bore 39 and bore 40" (see Figure 8). Endwise movement of plunger valve 43 is limited by projections 44 and 45 on the end plug screws 46 and 47 respectively and it Well be seen from Figures 5 and 8 that when the rotor is being driven in the direction indicated (counterclockwise) liquid under pressure will pass through the port 39, passage 39', and bore 39" and act upon the end of plunger 43 to force same to its extreme right-hand position (Figure 8) against the stop projection 45. With plunger 43 in this position liquid under pressure passes freely through the bore 39" into chamber 31 and on through the hollow shaft 30 as previously described.

If it is desired to reverse the rotation of the pump rotor and thus change the direction of iow through the pump in such a manner that liquid will be taken in through the opening 9 and discharged through opening S, such reversal of the rotation of rotor R will cause the pump discharge pressure to be established in the port 40 and the passage 40. When this occurs the plunger 43 will be moved to the left (Figure 8) against the stop projection 44 thus permitting liquid under pump discharge pressure to enter chamber 31 through port 48 and passage 40. Liquid is prevented by the plunger valve 43 from passing back to the low pressure side of the pump through passage 39' and port 39 and thus the efliciency of the pump is in no way diminished. Our above described arrangement for supplying liquid under pressure to urge the rotor vanes outwardly is rugged, fool-proof, inexpensive, and effective and automatically functions without any attention from the operator to insure a proper supply of vane sealing pressure regardless of the direction in which the pump is operated.

In the opposite or driveshaft supporting housing B a pair of ports 48 and 49, corresponding in form and location to ports 39 and 40 just described, are provided. These ports are seen in Figures 4, 6, and 7 and it will be observed that port 4S connects to a valve chamber 50 in mined safe value".V f

f 53 and l54 'extend'from chamber 52 into valve chambers 50 and 51 respectively; The inner ends of passagesA 53 i i and 54 are formed 'as conical valve seats 53' and 54' for the valves 55H and 56 which are' here illustrated as ball typefvalves.` A spring 57 urges valve 55 toward its seat 53 and is located by a stud 5810,11 screw plug 59.` In like mannerjspring 60`urgesvalve 56 toward its seat 54 and is located by a stud 61 on screw plug 62.

It will be'` seen from Figures 3, 5, and 7 that the shaft bearing 18 extends into Ythev chamber 52 and the function Vof the double ball valve arrangement just described is to permit the oil orotherlliqiud being pumped to pass outwardly between the bushing 18 and driveshaft D to provide positive lubrication therefor but to prevent excessive pressure from building up in chamber 52 against the oil seal orstuiting boxarrangem'ent indicated at 34 which 'might' cause leakagetherethrough. With our ball valve arrangement pressureI within the chamber 52 isr autop maticall'y'maintained at or below av desired predetermined maximum value regardless of the direction of rotation of the pump rotor. With Vthe rotorbeing driven in the 9 direction indicated by the arrow in Figure 6', which is the same direction as indicated in Figure V4, uid under the pump discharge pressure will be forced through the passage w 48 into the valve chamber 50 and will tend to maintain the ball valve 55 seated against the seat 53.

Liquid which enters the chamber 52 around the shaft D is also n `under substantially the pump discharge pressure and, when chamber 52 becomes filled with liquid, the ball valve 56 `rnay be pushed downwardly againstthe spring 60 into open position as seen in Figure 6 permittingthe escape of liquid from chamber 52 back` into the suction or inlet sideof the `pump through the passage 49. The spring `6i) will, ofcourse, be of vsuch strength and be so `adjusted that j -Qthe valve 56 will open Whenever `a pressure `is built up in chamber 52 such that there is danger of leakage past the 011 seal l34'. 'Thus the ballvalve 56 inA eiect becames a pressure regulating. valve for;` maintaining the' pressure which can be built'upin chamber 52 below a predeter- If the pump is operated in the oppositel directionffrom that indicated in Figure 6 the `functions of valves 55 and 56 automatically are reversedy and'valve 56 becomes effective to seal ofthe high pressure sideof the pump from the chamber 52 whilefvalve 55 acts Iasy a pressure regulating valve to limit the pressure which can build up in chamber 572 and tofbleed excess liquid which enters chamber 52 back into the inlet side ofthe pump. It will be. understood from the above description of our improved automatic `bleed valve arrangement that, regardless of the dlrectlon of rotation of the pump rotor, a build up of excessive pressure 4against the drive shaft stuiing box or oil seal 34 will be automatically and positively prevented. No attention is requiredonthe part of the operator to effect the changeover in functioning of our .automatic control when the .direction of rotation of the pump is changed and our arrangement accordingly insures positive lubrication of the main shaft bearing inthe bushing 18 at all times. w p

The automatic dischargerpressure control means-will w now be described. The housing His formed with a center web 63 (see Figures 3 and 4) which extends in the direcvtion of the axis of rotation of rotor R and separates the "passage `13 from the` passage 16. It will be noted that 4 these passageshave downwardly extending portions 13 p and 16 disposed on opposite sides of web 63 and that a communication orfby-pass port 64 extends through web 63 and is adapted to connect passages 13v and 16. Port 64 is formed with oppositely, facing valve seats 65 and 66 and the housing H isbored to provide similar cylindrical f6 openings 67 and 68 symmetricallyarranged on opposite sides of the web 63 and axially aligned with each other and with the communication vport 64. i

As illustrated in FigureV 4, in which the purnpis' ar;- ranged for rotation of the rotor in counterclockwise d1- rec'tion and fluid ow from right to left, a cylinder niemyber 69 4havinga closed outer end and open inner end is `its opposite end. A suitable piston sealing means,` such as a piston ring indicated at 73', is preferably provided to reduce possible leakage past the piston 73 which, as will appear later, is subjected on one end to the relatively low pressure of the pump inlet and on its other endlto the relatively high pressure of the pump outlet.` Extendingfrom the closed end74`of piston 73 is a hollow valve stem member 75 which carries" a puppet valve 76` having a seating face 77 disposed to coact with valve seat 66 in web 63 to close the communicating port 64 between the passages 13 and 16. The hollow valve stem 75 extends beyond the poppet valve 76, as indicated at 75" and forms a guide for the* pressure regulating spring 78 onefendof which abuts against the poppet valve 76 and the other end against an adjustable abutment 79. Adjusting screw extends through the end cover plate 71 and has a attened outer end portion 81 adapted to be certain limits by' releasing the' lock nut 85 and turning the screw 80 by means of its tlat end S1 tocause the abutmentl member 79 to move axially on screw 80 and thus increase or reduce the compression of spring 78. A tapered. shoulder 80 on screw 80 is adapted to seat on a corresponding seat in cover plate '71 and spring 78 tends to hold shoulder 80' seated even when lock nut 85 is loosened, thus preventing leakage at all times,A Y

The end 7'5' of' the hollow valve stern 75 opens into the cylindrical chamber or opening 68 and thus is connected directly with the passage 13-'13 of the housing H.

`When the rotor is Vbeing driven in ounte'rclockwise direction as seen in Figure 4 passage 13 is one of the low pres sure inlets and accordingly the low pump suction or intake pressure will prevailthr'oughout the chambers llt-"13", cylindrical `opening 68, the interior of tubular valve stein 75, cylinder 69 and against the left-hand (Figure 4) end of piston 73. The pressure on the opposite' side of web 63 in passage 16-16 will however be the high pump discharge pressure. against the outer surface of the end wall 74 of piston 73 andalso against the left-hand side (Figure 4) of puppet valve 76. v A

It will be noted that the area of the poppe't valve 76 which is exposed to the pump discharge pressure is greater thanthe area of the piston 73 which is` exposed to the same pressure. Accordingly the pump discharge pressure willexert a force urging the valve 76 towards open position to the right in Figure 4) which is equal to the'r dirference in the exposed areas of valve 76 and piston end 74 multiplied by the pump outlet pressure in the passage 16. By making the diierence in the effective areas of the valve and piston relatively small a relatively small force willl be .exertedtending to move the valve-'piston assembly toward This high pressure will be effective ing by-pass control to be made in an exceedingly compact 'form and susceptible to easy and accurate adjustment.

`lbs. the pressure differential eifective to move valve 76 will be sufficient to Overcome the spring 78 and open valve 76 permitting fluid to be by-passed from the pump outlet 16 back into the low pressure inlet 13, thus preventing excessive pump discharge pressure. This by-pass pressure control is, of course, entirely automatic and the maximum discharge pressure may be varied by changing the spring 78 or by adjustments thereof through the screw 30 and abutment 79.

It is a feature of our invention that the automatic discharge pressure control mechanism just described may easily be reversed when it is desired to reverse the-rotation of the pump rotor. This reversal of the parts is possible because the cylindrical openingsv 67 and 68 are identical .and it is only necessary to remove the screws 70 and 72, reverse the positions of the cylinder 69 andend cover plate 71 and at the same time reverse the piston 73 and valve 76 so that the valve 76 will seat upon seat 65 on the opposite side of web 63. This operation may be effected in a very short time without special equipment or skill. As our improved pump includes automatic controls whereby the pump output pressure is applied to the inner l edges of the vanes regardless of the direction of pump rotation and automatic means for control of the bleed-off of oil passing through the main shaft bushing regardless of direction of pump rotation, it will be seen that with the pump disclosed herein it is only necessary to reversel the pressure control valve 76 in order to change over the pump fromoperation in one direction to operation in the opposite direction. The pump is exactly as effective and etcient in either direction of rotation.

If the pump discharge pressure control is not desired or necessary, the valve 76 may be blocked in closed position by interposing a suitable block member (not shown) between the screw Sil and the end of valve stern extension 7S to hold valve 76 seated on the web 63. When the pump is so operated with valve '76 locked in closed position it may be reversed without any attention whatever on the part of the operator. It will also be understood that for some service requirements or vconditions it may be desirable to supply pumps in which the discharge pressure control by-pass is omitted in which case the by-pass port 6ft will be omitted and the web 63 left solid. Such n pumps, of course, retain all of the other advantageous features of our automatically reversible vane type balanced rotor pump.

It will be seen from Vthe above description of our irnproved pump that We have provided a pressure control by-pass arrangement which eliminates the necessity for heavy springs and may readily be reversed to accommodate changes in pump rotation. The present application, which is directed to this arrangement, is a division of our prior application Serial No. 35,618, led June 28, 1948 for Rotary Pump, now Patent No. 2,696,787'dated December 14, 195.4.

An incidental feature of our improved pump design is the arrangement of the keys 23 and29 which effect driving connection between the main shaft D and the rotor R. As is seen in Figure l) the bore 22 in rotor R is provided with a circumferential groove 86. Opposed key slots S7 and @8 (Figure 9) are also formed in the bore ZZof rotor R aud corresponding key slots 89 and 9@ are cut into the shaft D. The keys 2S and 29 are held inA position the slots 87 and S3 of rotor R by a split expansion ring 9ll,v of spring wire or the like, which engages suitable grooves in the ends of keys 28 and 29 and also lies in the groove 86 of rotor R. This arrangement isA clearly illustrated in Figure 3 and it makes it possible to maintain thev inner end'of shaft D at the full diameter of the bore in bushing 18 while still permitting the shaft to be assembled after the rotor has been installed in the pump chamber 3. With the key Support illustrated and described the entire end unit B can be removed by taking out screws 2 and withdrawing the housing B and shaft D from the housing H. If the keys 28 and 29 were supportedrin the shaftin the usual manner, instead of being held in the shaft receiving hole in rotor R. this mode of assembly and disassembly would not be possible.

Although we have described the invention in considerable detail, it will be understood that variations and modications may be made in the form, proportions, and arrangement of parts. We do not wish to be limited to the specific structure shown and described but claim as our invention all embodiments thereof coming within the scope of the appended claims.

We claim:

l. A vane type rotary pump includingy a housing structure having a pump chamber, said pump chamber having an inlet portand a discharge port, a rotor supported substantially in line contact with the wall of said pump chamber for rotation therein, said housing having an inlet opening and a discharge opening and inlet and discharge passages leading respectively from said inlet opening to said inlet port and from said discharge port ,to said discharge opening, a wall between said passages having a bypass port extending therethrough, oppositely facing valve seats at said bly-pass port, said housing having a pair of identical cylindrical bores axially alignedy with said bypassport and disposed on opposite sides thereof, an open `ended cylinder removably secured in one of said bores,

v means between said abutment and said valve, said spring means tending to hold said valve seated, Vone end of said piston and ythe adjacent side of-saidvalve being exposed to uid in said pump discharge passage, the exposed area of said side of said valve being greater than the exposed area'ofsaid one end of said piston, and said tubular valve stem connecting said pump inlet passage to said cylinder whereby the other end of said piston is exposed to the pump inlet pressure.

-2. A vane type rotary pump including a housing structure having a pump chamber, said pump chamber having an inlet port and a discharge port, a rotor supported substantially in line contact with the wall vof said pump chamber for rotation therein, said housing having an inlet opening and a'discharge opening and inlet and discharge passages leading respectively from said inlet opening to said inlet port and from said discharge port to said discharge opening, a wall between said passages having a by-pass port extending therethrough, oppositely facing valve seats at said by-pass port, said housing having a pair of identical cylindrical bores axially aligned with said byn pass port and disposed on opposite sides thereof, an open ended cylinder removably secured in'one of said bores, an

lend cover plate removably secured at the outer end of the other ofsaid bores, apiston disposed in said cylinder,

' a tubular valve stem member projecting from said piston,

, :of said side fof said valve being greater than the exposed tion of said pump rotor.,

Y area of said one end of said piston, said tubular valve Vstern'` connecting said pump inlet passage to said cylinder `whereby the other end of said piston is `exposed to pump inlet pressure, said cylinder and end cover plate being nterchangeable and said piston,` valve stem, valve, and spring being reversible to accommodate reversal of rota- 10 Roessler Nov. 29, Peter June 6, Storch et al'. May, 2, Shoemaker Sept. 28, Kendrick Oct. 30, Robinson et al. Dec. 5, Wright Mar. 9, Jaworowski et al Dec. 14,

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