US2687696A - Diaphragm pump - Google Patents

Description

Aug. 31, 1954 v E. E. THEls 2,687,696 DIAPHRAGM PUMP Filed Feb. 8, 1951 2 Sheets-Sheet l Invenr [mer E.y Theis H 5 //forqy..

Filed Feb. 8, 1951 Allg. 3l, 1954 E E, TH E1s 2,687,696

DIAPHRAGM PUMP l2 sheets-sheet 2 Patented Aug. 31,1954 I 2,537,696

'rss PATENT OFFICE DIAPHRAGM PUMP Elmer E. Theis, Jacksonville, Fla. Application February 8, 1951, Serial No. 209,930 i3 Claims. (Cl. 103-150) UNITED t sT My invention relates to positive displacement ment; and Fig. 6 is a top View of a part of the pumps and parts thereof, and particularly condrive arrangement taken on line -i5 of Fig. 5 cerns diaphragm pumps. and comprising members shown in the right hand A general object of my invention is to provide portion of Fi 1. an improved diaphragm pump, and, more speci 5 Referring now tothe drawings, Fig. l discloses cally, to improve the reliability and operating a pump comprising a diaphragm I operating in, eiliciency of diaphragm pumps. and formingthe movable wall of, a displacement A` specific objectof my invention is to provide or pump chamber 2 in a casting 3. An inlet. an improved diaphragm pump of the type having vacuum, or suction chamber and an outlet, disa vertically disposed diaphragm, to minimize 10 charge, or compression chamber are providedin lubrlcation difficulties 1n such pumps, and to proa casting 4, and this casting 1s attached to the Vide self-priming characteristics and improved casting 3 with the inlet and outlet chambers valve operation thereof separated from the pump chamber by a valve It is a further specinc object to provide a selfassembly 5. A third maior casting B is attached priming diaphragm pump wherein the diaphragm to the pump chamber casting t by means of bolts is not subjected to the pressure of the outlet con-` 7, and COIHDI'SSS mOUDHg legs and 55 t0 SUD- duit when the pump is idle. port the whole pump assembly, a trough or basin Anotherobject is to provide a flap of flutter I0 partially filled with a quantity of oil II, and valve construction, particularly adapted for use bearings for a main drive shaft I2. Arms I 3` in positive displacement pumps, which is inex- 2o connect the trough to an annular flange portion A further specic object of my invention is to Clamp the peripheral portion l5 0f the Circular provide a diaphragm pump in which the load diaphragm between the flanges. A yoke or con-.-

imposed on the driving mechanism is maintained necng I'Od I7 iS arranged t0 drive the da approximately constant through a wide range of Dhragm il'l and Out 0f Dump Chamber 2 thfllgh differential pressures across the pump. the operation of a journal i8 having an eccen An additional object is to minimize, in a liquid bore which is carried on the shaft I2 and rotates pump, erratic operation and Wearing effects due with the shaft in a bearing I9 in boss iid of the to sand or other `foreign matter in the liquid. connecting rod I 1. Shaft I2 is rotated by a suit- The specific embodiment of my invention deable motor 2I, which, through belt 22, drives a scribed herein, and shown in the accompanying pulley 23 mounted on the end of shaft l2.

drawings, comprises a diaphragm pump particu- Diaphragm I may be a at sheet or disc of larly adaptedlfor pumping Water from a shallow rubber, synthetic rubber, leather, or other suit- Well and for similar purposes, but it will be able material, and it completely closes the circuare adapted to other apparatus and other uses. 3, being there held in place between the anges `'Ihese novel features which I believe to be charw I4 and I5 by means of the bolts l. These bolts acteristic of my invention are set forth with parpass through suitable openings in the frange ifi ticularity in the appended claims. My invention 4U andin the peripheral portion it of the diaitself, however, both as to its organization and phragm, and are threaded into bores in the method of operation, together with further 0b flange I5.

jects and advantages thereof, may vbest be under Connecting rod Il` terminates at the dia stood by reference to `the following description phragm in an enlarged plate 2t, of which the taken in connection with the accompanying face 25 in contact with the diaphragm is suitably drawings, in which Fig. l is a partially sectionbeveled from a flat central portion in the direcalong the line 2-2 of Fig. l; Fig. 3 is a top view diaphragm- Facing the plate 24 0H the Other of the inlet and outlet valve assembly for the 5o side of the diahpragm is a Second substantially pump of Figs. 1 and 2; Fig. 4 is a detail side View similar plate 26 bolted by bolts 27 through the of a portion of the valve assembly of Fig. 3; Fig. diaphragm to the plate 24. These bolts 2l eX or washer for each of the bolts 21 and the bolt holes in the plates 2li and 2E. Starting from the diaphragm, the connecting rod I1 is shaped or formed in an upward direction for most of its length, and terminates in a downward extension which, in part, comprises boss 20. Accordingl", boss 20 may be disposed in the bath of oil II in the trough l while the connecting rod extends up and over the retaining wall 28 of the trough, and any extension ofthe wall, such as is provided by the portion Z9 of splash cover 3o. This splash cover comprises a hoodlike central portion 3l which extends up over a portion of the connecting rod, and over the otherwise exposed portion of the trough, to prevent the oil from splashing out, to prevent foreign matter, such as water or undesired objects, from entering the oil bath, and to prevent accidental contact of external objects or parts of a person with this portion of the connecting rod.

The trough is conveniently filled to a predeter-, mined desired level of the oil bath II through a pipe elbow 32 closed by a plug 33. The plug is arranged so that when oil is poured into the elbow to the level of the top thereof, the oil in the trough is brought up to the desired level. This level is preferably at about the center of boss 2t, and shaft I2.

Bearing I9 in boss 20 of connecting rod I1 may comprise a bearing insert, as shown, or it may be simply a smooth cylindrical bore extending through the boss 2li. This bearing I9 cooperates with the cylindrical surface of journal member I8, through which extends an eccentric cylindrical bore to receive shaft I2. The eccentric journal member is keyed to the shaft by means of a set screw 34 threadably engaging in a threaded hole in the journal member, preferably at the thickest portion thereof. The set screw 34 may either bite into the surface of shaft I2, or it may, as shown in the drawing, extend into a keyway or indentation in shaft I2. Access to the set screw 34 is provided by means of an opening 35 extending through the boss 2t and bearing insert I9, the opening 35 being preferably large enough freely to pass set screw 34. Alternatively, set screw 34 may be sufficiently short to be withdrawable cornpletely into eccentric journal member I8 to clear the shaft l2 at the inner end and the surface of bearing I9 at the outer end. Adjustments to the set screw are made by rotating shaft I2 until the set screw aligns with the opening 35, permitting the insertion oi a set screw wrench or screwdriver, as required, through the opening 35. This operation is performed after the removal of the hood portion SI of splash member til, the hood being removably attached thereto by boltsl 3B.

The opening 35 which serves as the set screw access hole further operates to improve the lubrication of the bearing. Oil from the bath I I is free to enter or leave the bearing through this opening. The most satisfactory lubrication has been found to be obtained when an additional opening 36 is provided through the lower portion of the boss and bearing insert I9. When a lower opening is thus provided, oil is pumped through the bearing from the lower opening out through the upper opening 35. Whether or not opening 36 is provided, however, increased oil flow through the bearing and improved lubrication Vresult from the provision of opening 35.

Casting 4, which comprises an inlet, vacuum or suction chamber 3l, and an outlet, discharge or compression chamber not seen in Fig. 1Jv is provided with an 'inlet conduit 38 communicating with the suction chamber 3l, and an outlet conduit 353 communicating with the compression chamber. The inlet chamber is separated from the pump or displacement chamber 2 by the inlet portion @il of valve plate el covering a plurality of inlet valve ports 42 formed in the metal body member 43 of the valve assembly. The movable valve plate il is spring-loaded into the position to seal ports 52 by means of a compression spring et surrounding and bearing against the headil of a bolt threaded into a boss llt formed as part of the valve body t3. rfwo such springs, bolts, and bosses are provided for the inlet valve plate of the assembly 5 and an equal number for the outlet valve plate al'. As shown in Fig. l, in dotted lines, the outlet valve comprises a valve plate lil, biased toward closing position by compression springs i8 and 49.

llt will be understood that valve plate 4I isolates the suction chamber 3l from pump chamber 2 until the pressure in the pump chamber is sufficiently reduced to permit the pressure in chamber 3l to overcome the force of springs if-l and to lift, in. the downward direction, plate il from its seated position, thereby to partially uncover ports e2. The plate 6513 on the other hand, remains seated to isolate the compression chamber from the pump chamber until the pump chamber pressure is sufficient to lift plate l1 upwardly against the biasing force of springs uncover the outlet valve ports.

A suitable priming opening4 to permit the initial filling of chamber 3l and preferably conduit 38 is provided at the top of the suction chamber 3l and may be closed by a plug 50.

The motor 2 I, as shown in this ligure, is mounted on a platform pivotally supported by bolts Bil. Belt tension is readih7 adjusted by pivoting the motor and motor deck. about bolts 59', with the bolts slightly loosened, and thereafter tightening the bolts to hold the motor in its adjusted position. A further understanding of the motor mounting will be had from a later consideration of Fig. 5.

Rotation of shaft i2 and journal it in bearing I9 resulting from motor operation causes the boss 2t to travel in a circular path. This motion of the boss is translated into an horizontal rectilinear component at the center of face 25 of plate 2li. The whole plate, and with it, plate 26 and the central portion of diaphragm i, will be driven back and forth, in and out of chamber 2, to increase and decrease the volume and hence the pressure in the chamber. A slight tilting motion is also imparted to the plates but this is of small consequence and may be readily reduced if desired by increasing and diaphragm l. 28 are preferably at height above the ground or floor as the center of shaft 2t.

The centers of plates 256 and The motor 2 I, in a typical construction, may bev rated at one-third horsepower at i800 revolutions per minute, or a little less, and the ratio of pulley diameters may be such as to drive shaft 2b at a little more than 600 revolutions per minute. The diameter of eiective area of the diaphragm I., which is, of course, the diameter of the opening in chamber 2 covered by the diaphragm, may be. about 5 inches, and the diameter of plates 2li and 26, about Ll/z inches. The stroke of the diaphragm, taken at the center, may be of the order of one-quarter inch, and in pumping water from a shallow well in which the water level in the 5 the distance between shaft 2Q' approximately the same well isabout 18 feet below the pump and the threaded into suitable tapped openings in bosses water is being pumped against a tank pressure of 58 of body member 43. Two such bolts 62 are between 20 and 40 pounds per square inch, a pump provided for the plate 4l, and the compression with these dimensions constructed in accord with springs 48 and 49, as seen in Figs. 1, 2 and 4, bias my invention will have a capacity of approXithe plate 4l into the position to cover ports 59. mately 6 or 7 gallons per minute. When the pressure in chamber 2 increases suf- Referring now to Fig. 2, which is a sectional nciently, plate 4'! is lifted away from the surface view taken along line 2`2 of Fig. 1, it will be of seat member 6| to permit the escape of seen that the suction chamber 3l is separated liquid under the plate 4l' into outlet or compresfrom compression chamber 5I byvay dividing wall l0 -sion Chamber 5|.

52, and the bottom of each of` the side walls of The inlet valve arrangement is similar to that each chamber conforms to a predetermined of the outlet valve but is oriented to supply liquid formed as a part of casting 3 extending under l5 resilient member 63, which maybe affixed if portion of chamber 2 into two compartments. A tien 4G Of Valve bedy member 43- POrts 42 eX- of the valve assembly is disposed against the biases plate 4l into the seated DOstiOn against against the casting 4. A similar gasket 54 is arinlet Valve by COVerng p01ts 42.' It Will be linderranged between the under side of the valve body stood that a second spring similar t0 spring 44 is including the top of the web member 52', BOM-,S this second portion of the plate. The bolt head 55 and 5t in connection with suitable lug ex- 45 seen in Flesl and 2 which hOlds spring 44 tensions serve to hold the castings 3 and 4 tightly against plete 4| is arranged in e lJOSitiOn under together against the valve body member and bess 46, as seen in Fig. 3, and a Similar bolt heed,

gaskets. The remaining portions of the pump net Sh0Wn,1s arranged under boss 5l. The bolts inlet and outlet conduits 38 and 39, indicated tapped Openings t0 e depth suel'ent to prOVde in dashed lines, and plug su, motor 2|, belt 22, the desired proper biasing force against the pulley 23, trough 10,130155 1, flange |5, diaphragm plates and are individually adjusted to equalize l, and plate 2o are each identined in this figure to 35 the biasing force of each respective spring of accord with the above discussion in respect to` cach plate, whereby the plates are lifted directly F1g 1 away from their valve seats by the actuating The construction of the valve assembly is most pressure, and n0 Substantial amount 0f tiltiner readily understood from a consideration of Fig. 0f the plates OeCurS.

3, a top View of the assembly, and Fig. 4, a sec- 40 The bypass conduit or port 6!) is seen in Fig. 2

tional detail view of a portion of the assembly to connect or communicate between inlet charm.

The valve body member 43 'is essentially a flat In practice, the diameter 0f the Conduit te may plate, but it is provided with a cup-shaped inlet 45 be applOXimately one thirty-second (12) of an the drawings. The body member is provided bypass pOlt, eCCOldingly, is Of the Order 0f 250:1. with three aligned inlet ports 42, three similar These dnlensions are aDlGrOXilnate and are Set aligned outlet ports 59 and an inlet valve by.. forth to indicate the orders of magnitude only. pass @ondule 5g m the form of a, Smau openmg Fig 2 additionally discloses a sniftei' valve extendlng through the body member and ar.. i4 1X1 COInmllIllCELtlOn With the Chamber 2. AS ranged to communicate constantly, that 1s with SllOWn e Valve CeD 65 Closes this Valve In use out being closed at any time, between the inlet 1n e Diessure tenk Water supply system 110W- or suction chamber 3l and the pump chamber 2. eveil the Cep 1s replaced by e tube COIlneCtlng The outlet portion of the valve assembly com the shifter valve to a control which admits air prises the movable valve plate 41, `which is prefinto the chamber 2 whenever the water level in erably generally rectangular in shape. This` the pressure tank Of the System ISBS abOVe a plate seats against a resilient seat member 6|, 50 predetermined Peint. When this Occurs, air iS which is preferably made of synthetic rubber, admitted to the valve 64 and is sucked into the or the like, and which is preferably of the shape chamber 2 at each suction stroke of the pump t0 of plate 4'! but slightly larger in dimensions. be pumped into chamber 5i and thence to pass The resilient member 6l may be affixed to valve into` the pressure tank of the system. Such conbody member 43 by the use of a suitable adhe- 65 trol of pressure systems is known to those familiar sive, although it has been found that so long as with such systems. The shifter valve itself coninember 6l is not ailixed to the movable plate il veni'ently comprises a construction substantially rapidity. Ports 59, of course, extend through identied as valve 64.

both the member 43 and the member 6|. Bolts Fig. 5 is a view of the pump, partially cut away, 62, as best shown in Fig. 4, extend through the taken from the end opposite that shown in Fig. 2. plate 41 with a free or clearance t and through In Fig. `5, certain portions of the pump heretofore the resilient seat member 6I, and they are 75 described have been identied by the reference numerals corresponding to those used in Figs. l through e, and further description of many of these parts is not required in connection with this figure since the descriptions heretofore given apply in the same manner.

The drive arrangement for connecting rod l1 is clearly shown in Fig. to comprise shaft l2 supported to rotate in bearing inserts @6 and 61, which, in turn, are arranged in suitably bored bosses extending inwardly from the end walls into trough l. Oil is prevented iro-m leaking along the shaft l2 out oi the trough at opposed ends thereof by a sealing plug t8 and by a shaft oilv seal iid, respectively, the latter being preferably of the known type making use of a synthetic rubber member surrounding and held in contact with the shaft by means oi an annular tension spring. The shaft I2 is lubricated in bearings St and @l by means of grooves or ducts '153 formed on the lower inner surfaces oi these bearings, the ducts being below the normal level o the oil H. The oil so supplied is permitted to drain back into the oil bath through openings "il bored through the top and bottom portions oi bearings or bearing inserts B and @l and through the bosses carrying these bearings. It has been found that the provision of openings 'lil helps to retard pump of oil toward the ends of the shaft, thereby to minimize oil leakage through the seals Gli and t9. Housing 3e, including the raised central portion 3 l, prevents contamination of the oil passing through upward openings Tl, and prevents any or this oil from splashing out of the trough. The trough cover 39 is held in place by bolts l2, which thread into the trough body, and a gasket 'i3 is preferably provided under the cover to prevent any leakage out under the edges thereoi.

Fig. 6 is a top View taken along the line 6-6 of Fig. 5 and clearly discloses bosses 1d and 15 which, respectively, hold bearing inserts 56 and el, and which are formed as part of the end walls cf the casting comprising the trough.

Openings 'il extend down through the bosses to communicate with the bearing surfaces of shaft l2. Holes 'i6 extend into the trough body and are internally tapped to receive the cover hold-down bolts. The positions of theset screw access opening 35 and of the set screw 34 are further shown in Fig. 6. It will Ybe noted that the shaft is shown not in the position to provide access to the set screw in this view. Fig. 6 also showsl the oil fill opening 32 and plug 33.

Arms it are partly shown in each of Figs. 5 and 6, these arms being provided to connect the portion of casting El which comprises the oil trough lll to the portion or" this casting which includes the flange Hl for the outer face or" the diaphragm, as described in connection with Fig. l. It will be understood that the motor pivot bolts all' are threaded into suitable upward extensions or the arms I3 to support the motor mounting platiorm. This arrangement will be most readily understood by taking Figs. 1 and 5 together.

In typical operation of the pump in a shallow well and pressure tank water supply system, an extension of pipe or conduit t may lead down a well into a body of water, of which the level should not be more than about 22 feet below the pump, the conduit terminating below the water level in a foot valve, and an extension of pipe 39 may be connected to a pressure tank which is to be partially filled with water, the remainder of the tank above the water to contain a pocket vsome of the air originally in of air under pressure. The pressure in the tank may be maintained by the pump at from about 20 to about 40 pounds` per square inch, and suitable automatic controls are preferably provided to maintain the desired water level, or pressure, or both, in the tank. Such controls may, for example, start the pump motor when the tank pressure drops to a predetermined minimum, such as 20 pounds per square inch, shut ofi the motor when the pressure reaches a desired maximum, such as Ll() pounds per square inch, and may admit air to the displacement chamber through shifter valve GB when the water level exceeds a predetermined height in the tank, whereby the pump will force additional air into the tank.

The pump is prepared for' initial operation in such a system by removing priming plug 5t and `filling the inlet or suction chamber 31 and conduit 35 with clean water, thereafter replacing the plug. As the pump motor starts operating to drive plates 24 and 'i6 and diaphragm l in and out of chamber 2, it is necessary that the water in chamber 3'! be drawn into the pump chamber 2, since the pump chamber would otherwise continue ull oi air and no Valve operation or pump action would occur. As the pump starts operation, it is necessary, if water is to be drawn into the pump or displacement chamber from the suction chamber through the inlet valve, that the pressure in the pump chamber must be reduced below atmospheric pressure by an amount slightly greater than the head of water above 'the well level plus the spring biasing force against inlet valve plate lll.V To fuliill this requirement, the pressure in the pump chamber may have to be reduced, for example, by almost one-half atmosphere. The volumetric change in the pump chamber produced by a stroke of the diaphragm, however, is a small percentage of the total volume.

Accordingly, except for the provision of bypass opening 6D, it is probable that pumping would not start. This opening provides an escape for the pump chamber back into the suction chamber. On a suction stroke, as the pump is started, a very small amount of water is drawn into the pump chamber, although no water may be drawn well into conduit 3a through the foot valve, as permitted by expansion of the air trapped in the inlet system, and this will occur even though the amount or such air is very small. The water so sucked in falls to the bottom of the pump chamber, and on the following compression stroke some air is forced upwardly through bypass conduit S8 to bubble up to the top of the suction chamber. At the same time air may or may not be pumped through the outlet valve depending on the back pressure in the outlet system and the spring bias o-n the outlet valve plate. In either case, the next suction stroke will produce increased suction rorce, that is, a lower absolute pressure in the pump chamber, which will suck a larger amount oi water from the inlet chamber. The increased amount of air in the inlet system assists, of course, in this increase, as does the water in the pump chamber. The next compression stroke forces additional air through conduit G0 further to increase the intake of water into the pump chamber on the succeeding suction stroke. As more and more water enters the pump chamber, the tendency is to pump increasingly great amounts of air into the outlet chamber atl each compression stroke, since a greater from the 2,687,696, g w ,y 9 1o air pressure is produced when the pump chamdiaphragm and on plate 26. If the diiierence ber contains more water. in head between the diaphragm and the well As the pump chamber fills more and more water level is 1'7 feet, the differential pressure withwater, the absolute pressure in the pump will `be about 7 pounds per square inch. Of

may be l feet below the pump. rJhe remaining l0 deal more certain than would be starting, for

pletely in operation. phragin is also increased when it is subjected to The conduit `6!! further operates automatically the lower dilerential pressure during stand-by to overcome Obstacles which W0u1d otherwise l5 periods. It will be noted that the diiTerential prevent pumping. For example, if the well level pressure on the diaphragm during stand-by peis very low, or if the pressure in the outlet sysliods as given in the above example is with the tem or the bias on the outlet valve plate is high, assumption that the foot valve at the lower end or if the foot valve is leaky, a large pocket of of the inlet conduit is lea-ky. Asmentioned above,

watei In this case, the water level in the sucprovided as described will be appreelably less tion chamber may drop to the level of conduit 60 It is to be further noted that a small poclet but it will not ordinarily drop below It is beof air in the suction chamber will permit together lieved that the reason 1s that on suction strokes 20 with conduit BU, slow speed operation of the pump occurring after the water level reaches the conwith very low load on the motor since water may mixes with the water i'n the pump chamber and 30 ployed having astarting torque much lower than valve ports. O-n compression strokes some air motion of the diaphragm on starting may have and water are forced back into the suction chamto be against the full storage tank pressure.

ber through conduit 60 partially replenishing any A still further advantage of conduit 69 lies water that may have been sucked` through the 35 in its effect in maintaining more constant the 'inletvalve and the air in the pockets aroundthe load on the pump motor in pumping against this air into the outlet chamber, while retaining 40 tion chamber on each pressure stroke, since the c probably enough under most circumstances to valve against this low pressure, but as the tank keep the cup-shaped portion 4Q of valve body 4| pressure is increased, the pump chamber pressubstantially fille 45 sure will also increase. At greater pressures, When suicientair has thus been'pumped from however, more water will be forced back through `suction chamber will still contain a large volume which the motor must operate to overcome the of air. As pump operation continues, however, full tank pressure is decreased. Accordingly,

chamber. higher maximum pressure at lower rates without A `further important advantage of the conduit overheating or overloading the motor.

6U is in removing the starting'load on the pump From the foregoing discussion, it will be apmotor and in providing only a relatively small parentthat several of the advantages stemming force on the diaphragm during stand-by periods. fiom the piovision of conduit 6l) depend in part After a period of pumping, the motor being deon the specic location of the conduit above the diaphragm is thus equal to the force necessary motor load is 4concerned than in its priming-.functo maintain the water in conduit 38 above the tion earlier considered, wherein its location above level in the well, assuming that some leakage may the inlet valve and below the level of the connecoccur` through the foot valve. This force is of tion of the inlet conduit with the inlet chamber the order of one-half atmosphere or less and is are of more importance.

on` plate 24, and the lower pressure of the water may modications will occurto those skilled in in the pump chamber on the other face of the the art, and I therefore wish to have it under- 11 stood that I intend, in the appended claims, to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by United States Letters Patent is:

l. In a diaphragm pump, means forming a pump chamber having a top wall and a side wall comprising a substantially vertical flexible diaphragm, an inlet flap valve and an outlet nap valve in said top wall, means forming an inlet chamber and an outlet chamber each disposed above said pump chamber and arranged for periodic alternating communication therewith through said respective valves, and a conduit relatively much smaller than said inlet valve in communication between said inlet chamber and said pump chamber at least while said inlet valve is closed.

2. In a diaphragm pump, the combination in accord with claim l wherein said outlet valve and said conduit are each located higher than said inlet valve. f

3. In a positive displacement pump, means forming a pump chamber having a top wall and a horizontally movable side wall, inlet and outlet valves mounted in the top wall of said chamber, a suction chamber separated by said inlet valve from said pump chamber, and a conduit of much smaller capacity than said inlet valve and in bypassing relation thereto.

fi. In a diaphragm pump, a pump chamber having a top wall including inlet and outlet valve ports and a side wall including a movable diaphragm, said top wall being formed to dispose said inlet valve port approximately at the level of the top oi the movable portion of said diaphragm and to dispose said outlet valve port at a higher level, a suction chamber and an outlet chamber communicating with said pump chamber through said respective valves, inlet and outlet valve ports, said top wall having a relatively restricted opening therethrough in bypassing relation to said inlet valve port.

5. In a positive displacement ment chamber having a top opening, a valve assembly comprising a generally ilat base plate proportioned to cover said opening and having a iirst portion and a second cup-shaped portion, a port in said first portion, a second port in said cup-shaped portion, said base ing being arranged to be substantially horizontally disposed to position said ports at different respective upper and lower levels, a valve plate below said base plate biased to cover said lower level port and a second valve plate above said base plate bised to cover said upper level port.

6. In a positive displacement pump, a displacement chamber having a top opening, a valve assembly comprising a generally ilat .base plate proportioned to cover said opening and having a rst portion and a second cup-shaped portion, a port in said nrst portion, a second port 4in said pump, a displacecup-shaped portion, said base plate and top opening being arranged to be substantially horizontally disposed to position said respective ports at diierent respective levels, whereby one said port is at an upper level higher than the relatively lower level of the other said port, a valve plate below said base plate biased to cover said lower level port and a second valve plate above said base i plate biased to cover said upper level port, and an opening much smaller than ,said ports extending through said base plate at the approximate level oi said upper level port in bypassing relation to vsaid lower level port.

plate and top open- 7. In a positive displacement pump, a displacement chamber having a generally horizontal upper wall, said upper wall being provided with an opening, and an inlet chamber, a valve assembly comprising a generally flat base plate covering said opening, an inlet port and an outlet port extending through said base plate, a perforate resilient sheet member disposed against the lower face or said base plate to register a perforation therein with said inlet port, a second perforate resilient sheet member disposed .against the upper face o said base plate to register a perforation therein with said outlet port, a valve plate for each said port biased to seat against said respective sheet members, said inlet chamber being separated from said displacement chamber by a portion of said base plate partially covered by said rst sheet member and said inlet port valve plate, and an opening within the bounds of said portion of said base plate constantly in communication therethrough between said inlet chamber and said displacement chamber.

8. In a positive displacement liquid pump, a displacement chamber having a top opening, a valve assembly comprising a generally liat base plate proportioned to cover said opening, spaced perforations in said plate forming valve ports, a valve plate for each face oi said base plate to cover respective distinct ones of said ports therein and spring means to bias said valve plates toward port covering positions, thereby to form an inlet and an outlet valve, a resilient sheet member disposed between each said valve plate and said base plate and having periorations to register with Said ports to afford a resilient valve seat for each said valve plate, said base plate having a bypass opening through said base plate adjacent one of said ports therein which is part of said inlet valve, said bypass opening being continuously open and much more restricted than said ports.

9. In a positive displacement pump, a displacement lchamber having a top opening, a valve assembly comprising a generally iiat plate proportioned to cover said opening and having a eupshaped portion, an inlet port and an outlet port extending through said plate, one of said ports being in said cup-like portion and the other spaced irom said portion, movable valve members for said inlet and outlet ports, respectively, means to bias sai-d members toward said plate to cover said respective ports, and resilient sheet means disposed between said valve members and said plate perforated to register with said ports to provide a resilient seat for each said valve' member at each said port.

l0. In a positive `diplacement pump, an open top pump chamber and inlet and compression chambers, said inlet and rcompression chambers being vopen at the bottom and being disposed side by side :above said pump chamber, a valve assembly to be interposed between said pump chamber and said inlet and compression chambers, said valve assembly comprising a metal member shaped to lie against the rim bounding the top opening of said pump chamber on one side .and against the rims of said inlet and compression chambers on the other side, ka rst portion of said member separating said compression chamber from said pump chamber and a second portion separating said inlet chamber from said pump chamber, said first portion having a flat area on said compression chamber side and said second portion having a flat :area on said pump chamber side, respective resilient seat members for each said area covering at least .a portion thereof and respective- 13, ly disposed on respective faces of said metal members, at least two aligned ports for each said area, each said portextending through said metal memconduit being relatively much than said valve ports in said second portion.

11. In a positive displacement pump, an open top pump chamber and inlet and compression chambers, said inlet and outlet chambers being members, area, each said port extending through said metal member and said respective seat member, a movable valve member comprising a metal plate for each said area disposed to lie against said respective seat members to close said ports, means to spring-load said plates into port closing position and arranged to permit said ports to open 13. In a diaphragm pump, an inletvalve and an outlet a restricted, continuously open conduit communicating at a level below said inlet opening between said inlet chamber and said pump chamber.

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