Pump and method of driving same

1. Field of the Invention

This invention pertains to the art of pumping and particularly to diaphragm pumps for paint spraying and the like usage.

2. Description of the Prior Art

Diaphragm pumps driven by liquids which vaporize during the suction stroke of the pump are known in the art, for example in the Paul W. Schlosser U.S. Pat. No. 3,254,845 granted June 7, 1966. These pumps utilize cavitation to effect vaporization and condensation of the driving liquid. The repeated vaporization and condensation causes rapid erosion and corrosion of the pump parts and useful driving fluids are limited to low boiling liquids.

The deficiencies of the prior art liquid driven diaphragm pumps are completely eliminated and improved pumping efficiency and useful pump life are provided by this invention which eliminates vaporization and condensation of driving liquid in a liquid driven diaphragm pump. According to this invention, the pump diaphragm is variably driven from a reciprocating piston having a constant stroke through a variable volume of liquid having a gas dissolved therein under conditions which never allow the liquid to vaporize and which operate according to Henry's Law. While it is preferred that the driving liquid have the gas dissolved therein under one phase of operation, it is possible to use a driving liquid composed of a mixture of liquid and undissolved gas which expand under certain operating conditions.

An important feature of this invention is the complete elimination of vaporization of driving liquid in the operation of a liquid driven diaphragm pump and the maintenance of the liquid phase of the driving liquid at all times.

Another important feature of this invention is the provision of a dead space occupied only by air, paint solvent vapor or the like compressible material, on the pumping side of the diaphragm which allows the diaphragm to move to prevent vaporization of driving liquid even under conditions where the flow of liquid being pumped is throttled or completely stopped. In spray-gun usage of the pumps of this invention, interruption of the flow of paint or the like being pumped is sudden and may be quite frequent. Displacement of the diaphragm at least partially into the pumping chamber during these sudden stop periods provides for an enlarged volume in the driving liquid chamber with a reduced overflow of driving liquid on the first power stroke following throttling or shut-off so that the next suction stroke cannot result in vaporization of any driving liquid because sufficient gas will be released from the liquid to fill the chamber without reducing pressure sufficient to accommodate boiling of the liquid.

More particularly, according to this invention, the driving liquid is preferably a lubricant such as oil and the gas is preferably air dissolved in this oil. Under atmospheric temperature and pressure conditions, about 4-8 % by volume of air is dissolved in a lubricating oil of relatively low viscosity and relatively high boiling point. A light hydraulic oil is satisfactory. Gases other than air might be dissolved in a suitable driving liquid, such as for example, nitrogen, oxygen, hydrogen, carbon dioxide and the like. Where lubrication is not a problem, the driving liquid may be water.

In general, the gas containing driving liquid is maintained under temperature and pressure conditions which will allow release of the dissolved or entrained gas only on the suction stroke of the pump following the throttling or stoppage of the pumping operation. The released gas is reintroduced into the driving liquid upon resumption of the pumping operation.

To ensure against possible vaporization of the driving liquid, the pressure of the driving liquid is never released to a point even close to the vapor pressure of the liquid and the pressure is maintained from 10 to 100 times the pressure at which vaporization could occur.

Temperatures of the driving fluid are maintained sufficiently low to avoid vaporization even at the lowest operating pressures by reducing any required recirculating of the driving fluid to a minimum.

After throttling or complete stoppage of flow of the liquid being pumped, the remaining volume in the driving liquid chamber is harmonized with the piston stroke so that the lowest pressure produced on the suction stroke of the piston remains above the boiling pressure of the driving liquid and the return stroke volume of the chamber is completed with gas freed or expanded from the driving liquid thereby preventing vaporization. At the end of the suction stroke the driving liquid chamber is completely filled with a mixture of the driving liquid and the released gas.

To ensure that this remaining volume of the driving liquid is sufficiently great to contain enough gas for completely filling the driving liquid chamber, the aforementioned dead space is provided in the pumping chamber even during full pumping operation so that diaphragm movement into the pumping chamber is not completely stopped even upon full throttled no-flow standby conditions.

The pumping chamber is fed througn an inlet check valve and the pumped liquid is withdrawn through an outlet check valve and a control valve such as a spray-gun. The chamber on the opposite side of the diaphragm containing the driving liquid and the driving piston is connected to a source chamber through a bypass with a pressure limiting valve and through a refill passage for replenishing the pumping liquid. The pressure limiting valve is adjustable to control the delivery pressure of the pump.

The pump piston must not be retracted during the suction stroke with too great a velocity since the gas dissolved or entrapped in the liquid may not be given enough time to be freed from the liquid. If the suction stroke proceeds at a rate slow enough to release the dissolved or entrapped gas, only enough gas will be freed to maintain a constant stroke without ever releasing the pressure sufficient to permit boiling of the driving liquid. The gas separation thus obeys the law of Henry, and it is only when the pump piston is withdrawn with too great a velocity that a hollow space created ahead of the piston may be filled with vapor of the driving liquid which during the next pressure stroke, of course, leads to the undesirable cavitation. The maximum pump velocity is chosen so that the law of Henry may apply to the freeing of the gas. Preferably, the piston should not have a retracting velocity above 1.0 to 1.5 meters per second.

To prevent the dead space in the pumping chamber from becoming filled with the pumping liquid during the subsequent suction strokes after a throttling or stoppage of flow of pumping liquid, a spring loaded inlet valve is preferably provided such that the spring characteristic and the mass inertia of the valve will not permit the valve to be opened by reduced pressure in the dead space of the pumping chamber. A spring having a rate of 75 grams per millimeter and a closing load of 300 grams is sufficient to maintain the dead space.

It is then an object of this invention to provide an improved diaphragm pump capable of being fully throttled and method of pumping through a driving liquid without vaporizing the driving liquid.

Another object of this invention is to provide a liquid driven diaphragm pump, useful for spray painting, having a wide range of delivery pressures and delivery rates without bypassing the material being pumped and without effecting vaporization of the driving liquid.

A further object of this invention is to provide a method of driving a diaphragm or the like through a liquid containing a dissolved or admixed gas freed during a throttling of the diaphragm stroke to prevent vaporization of the driving liquid.

A still further object of the invention is to provide a liquid driven diaphragm pump operating according to the law of Henry.

Another object of the invention is to provide a diaphragm pump with a dead space on the pumping side of the diaphragm which will accommodate movement of the diaphragm even when flow of the pumping liquid is stopped.

Another object of the invention is to provide a diaphragm type paint spray pump with an inlet valve so correlated with a liquid driven diaphragm as to maintain a void filled only with compressible air, vapors or the like in the pumping chamber during all conditions of operation.

A still further object of the invention is to provide a diaphragm pump driven by a constant stroke reciprocating piston through a lubricating liquid having a gas dissolved therein which is released from the liquid when the pumping operation is throttled or stopped.

Another object of the invention is to provide a diaphragm pump driven by a constant stroke reciprocating piston through a lubricating liquid having a gas dissolved therein and a dead space on the pumping side of the diaphragm so correlated with an inlet valve as to accommodate limited movement of the diaphragm when flow of the pump material is stopped so that only a small amount of the driving liquid need be released to accommodate the limited stroke of the diaphragm.

Other and further objects of this invention will become apparent to those skilled in this art from the following detailed descriptions of the annexed sheets of drawings which, by way of a preferred embodiment, show one form of the invention.

FIG. 1 is a somewhat diagrammatic longitudinal sectional view with parts in elevation of a diaphragm pump according to this invention for pumping paint to a spray-gun and illustrating the positions of the parts at the end of a suction stroke;

FIG. 2 is a view similar to FIG. 1 but illustrating the positions of the parts at the end of a pressure stroke;

FIG. 3 is a view similar to FIGS. 1 and 2 but illustrating the position of the parts during a pressure stroke following full throttling of the pumping operation;

FIG. 4 is a view similar to FIGS. 1 to 3 but illustrating the positions of the parts and the condition of the driving fluid at the end of a suction stroke following a pressure stroke after full throttling, as shown in FIG. 3;

FIG. 5 is a longitudinal cross-sectional view, with parts in elevation and with parts broken away, of one form of diaphragm pump according to this invention;

FIG. 6 is an enlarged longitudinal sectional view of the pumping side of the pump of FIG. 4;

FIG. 7 is an enlarged longitudinal sectional view of the driving side of the pump of FIG. 4;

FIG. 8 is an enlarged side elevational detail view with parts shown in cross-section of the diaphragm and support plate of the pump of FIG. 4;

FIG. 9 is a plan view of the support plate taken along the line IX--IX of FIG. 8.

In FIG. 1 there is schematically illustrated a diaphragm pump 1 according to this invention having a casing defining a first or pumping chamber 2 fed from a supply container 3 with liquid to be pumped such as paint or the like. Liquid from the container 3 is supplied to the chamber 2 through an inlet pipe 4 and inlet check valve 5. The pressurized liquid or pumpage is discharged through an outlet check valve 6 to a supply hose 7 to a paint spray-gun 8 having a control valve 9 throttling or completely stopping flow from the pumping chamber 2.

The pump 1 has an axially movable diaphragm 10 forming one wall of the chamber 2 and separating this chamber from a driving liquid chamber 11 to which driving pressure is intermittently applied and relieved by means of a piston pump generally identified at 12 and including a cylindrical chamber 13 slidably mounting a cylindrical piston 14 driven by a wobble plate 15 rotated by a driving motor 16.

The wobble plate 15 rotates in a container 17 for the driving liquid which communicates with the driving liquid chamber 11 behind the diaphragm 10 by means of an overflow passage 18 containing an adjustable pressure limiting valve 19. A refill passage 20 also joins the bottom portion of the container 17 with a refill slot 21 in the cylindrical chamber 13 receiving the piston 14. The slot 21 is uncovered by the piston 14 only at the end of the suction stroke of the piston and is otherwise closed by the piston.

The container 17 is partially filled with the driving liquid L to a liquid level LL, and the top of the chamber 17 may be vented to the atmosphere as at V. A spring S urges the piston 14 against the wobble plate 15. The wobble plate 15 in the container 17 agitates the liquid L insuring aeration with air from vent V.

The wobble plate 15 drives the piston 14 through a relatively short stroke from the rearmost suction stroke illustrated in FIG. 1 to the forward end of the power stroke illustrated in FIG. 2, and this reciprocation of the piston drives the liquid L ahead of the piston forcing the diaphragm 10 from its rearmost position in the chamber 11 as shown in FIG. 1 to its foremost position in the chamber 2, as illustrated in FIG. 2. The loss of driving liquid by leakage past the piston 14 is replenished on each driving stroke through the refill slot 21.

When the valve 9 of the spray-gun 8 throttles the full discharge through the outlet hose 7, the displacement of the diaphragm 10 is reduced and since at the moment of throttling the driving liquid behind the diaphragm in the chamber 11 is sufficient to force a full diaphragm stroke or displacement, some of the driving liquid must be displaced from the chamber so that the remaining portion will permit the reduced stroke of the diaphragm. For this purpose, the pressure limiting valve 19 in the return or overflow passage 18 is a spring loaded needle valve which is unseated on the first pressure stroke of the piston 14 following throttling or stoppage of flow from the pumping chamber 2.

As shown in FIGS. 1 and 2, the volume of the driving liquid behind the diaphragm remains constant when the pump is operated at capacity under a full stroke of the diaphragm. However, as shown in FIG. 3, when flow from the pumping chamber 2 is throttled or stopped, the diaphragm movement is reduced and the volume of the driving fluid behind the diaphragm must be reduced because the stroke of the piston remains the same. Thus, the needle valve 19 will open, allowing escape of driving fluid back to the container 17 only in an amount sufficient to reduce the volume of liquid behind the diaphragm for accommodating the reduced displacement of the diaphragm into the pumping chamber caused by the throttling of the discharge from the pumping chamber. The valve 19 will only open under the increased pressure created in the pumping chamber 2 and in turn on the driving liquid by the throttling. Then, on the suction or return stroke of the piston 14 the valve 19 will immediately close and since the piston 14 moves through a full stroke, there will be insufficient driving liquid remaining between the piston and diaphragm to fill the chamber 11 and the cylinder space ahead of the piston. Under these conditions, as shown in FIG. 4, the pressure on the driving liquid is reduced and the gas dissolved in the liquid is released according to the law of Henry to fill the chamber with gas G and liquid L without ever allowing the liquid L to vaporize. Thus, the remaining volume of the mixture of gas and driving liquid is automatically adjusted during the suction stroke to fill the reduced chamber caused by the reduced movement of the diaphragm.

If leakage should occur during further working strokes of the piston pump following initial throttling since the pressure in the chamber 11 at the end of the suction stroke of the pump piston as illustrated in FIG. 1 will be lower than the pressure in the supply container, 17, a small amount of replacement driving liquid is fed to the chamber through the passageway 20 only during the short time when the slot 21 is uncovered by the piston. In the event excess liquid is supplied through the refill passage 20, it will be returned to the container 17 through the passageway 18 since the resulting increased pressure in the chamber 11 will reopen the spring loaded needle valve 19 for this purpose.

When the throttle valve 9 of the spray-gun 8 is again fully opened so that full pumping performance of the pump 11 is permitted, the outlet check valve 6 will open reducing the pressure in the pumping chamber 2 and again allowing the diaphragm 10 to resume its full stroke. The driving liquid behind the diaphragm is then replenished from the container 17 via the passage 20 and slot 21 until the volume of the driving liquid again fills the chamber 11 and the gas is again dissolved into the driving liquid. Each working stroke of the piston 14 decreases the amount of freed gas in the chamber 11 until full pumping operation is again achieved.

To minimize return of pumping liquid from the chamber 11 back to the container 17 and to thereby decrease freeing of gas from the driving liquid to fill the chamber behind the diaphragm, the diaphragm is arranged so that it will always have some movement on a pressure stroke even when the throttle valve 9 of the spray-gun is completely closed and no discharge is permitted from the pumping chamber 2. To accomplish this movement of the diaphragm 10 into the pumping chamber 2 even under complete stoppage of discharge from the pumping chamber, the inlet check valve 5 is sufficiently biased to a closed position and the walls of the pumping chamber are so shaped that the pumping chamber 2 will never be completely filled and a dead space or void will be provided in the pumping chamber as illustrated at D around the periphery of the pumping chamber. Then, even though the valves 5 and 6 are completely closed trapping incompressible pumpage such as liquid paint in the chamber 2, the air or paint solvent vapor in the dead space D can still be compressed on the pressure stroke of the diaphragm to permit some displacement of the diaphragm into the pumping chamber. This displacement of the diaphragm even under fully closed outlet operation of the pump maintains the volume in the driving liquid chamber 11 closer to the volume of the chamber under fully opened pumping operation so that only a small overflow of liquid through the passage 18 will be needed to accommodate the reduced volume in the driving liquid chamber from the full pumping volume of the chamber. This, of course, reduces the amount of gas freed from the liquid required to fill the remaining volume of the driving chamber.

It will be understood that the pressure stroke of the pump piston 14 following a complete closing of the throttle valve 9 urges the diaphragm 10 through a complete stroke and this compresses the pumping liquid present in the chamber 2 an amount permitted by the dead space or void. If this pressure in the chamber 2 exceeds the pressure of the limiting valve 19 on the driving side of the diaphragm, some driving liquid will be returned to the supply container 17. Then on the following suction stroke, the pump piston 14 moves the diaphragm to rest against a support plate 22 as shown in FIG. 4, and the continued suction stroke decreases the pressure on the driving liquid to release the gas therefom. When the pressure at the end of the suction stroke has decreased the pressure in the driving chamber 11 to a point where it is below the pressure of the supply container 17, additional liquid will be supplied through the refill passage 20 when the slot 21 is uncovered by the piston. Then in a subsequent pressure stroke, the previously freed air in the chamber 11 is redissolved into the driving liquid and the diaphragm is moved into the pumping chamber 2 an amount permitted by the dead space until the pressure of the driving liquid is again increased sufficiently to open the pressure limiting valve. Then, on the next suction stroke the diaphragm 10 is again caused to bottom on the support disc 22 which will reduce the pressure in chamber 2 a small amount insufficient to open the check valve 5. Any leakage during the following strokes of the pump piston 14 is replenished from the supply container 17 through the refill passage 20 and slot 21.

In no event during the operation of the pump as illustrated in FIGS. 1 to 4 can vaporization occur in the pumping chamber 11, nor will the diaphragm movement be completely arrested even during standby operation where the throttle valve is completely closed. Thus, the pumping chamber 2 is never completely filled with the pumping liquid and the diaphragm never rests firmly against the wall of this chamber. In this manner, the remaining volume of the driving liquid in the chamber 11 may be maintained at a maximum and more than a sufficient supply of air from the driving liquid is available to prevent vaporization in the chamber 11. The heretofore encountered erosion and corrosion caused by vaporization in liquid driven diaphragm pumps is thus completely eliminated.

In the detailed drawings of FIGS. 5 through 8, parts corresponding with parts illustrated in FIGS. 1 to 4 have been marked with the same reference numerals.

The casing for the pump 1 as shown in FIG. 5 is formed from two half sections 30 and 31 shown separately in FIGS. 6 and 7. The half section 30 as best shown in FIG. 6 has a recess 32 in the face thereof mating with the opposing face of the section 31. This recess 32 receives an insert 33 preferably composed of corrosion and erosion resisting plastic material such as "Teflon" (polytetrafluoroethylene) or polypropylene. The exposed face of the plastic ring 33 is contoured around its inner peripheral portion 33a to provide a seat for the diaphragm 10 as hereinafter more fully explained and is recessed around its outer peripheral face portion as at 33b to provide for the aforementioned dead space.

The inlet valve 5 includes a poppet valve 34 with a head 34a seating on a valve seat insert ring 35 and with a stem 34b slidably mounted in the bore of a plastic bearing 36 which has radiating fins or webs 36a pressed in the inlet bore 37 of the casing part 30. A coil spring 38 surrounds the plastic bearing 36 and is bottomed at one end against the fins 36a and at the other end against a washer 39 backed by a nut 40 threaded on the valve stem 34b. Liquid such as paint from the inlet 4 flows around the bearing 36 through the spaces between the ribs 36a thereof to the head 34a which when seated on the ring 35 will seal off the inlet of paint to the pumping chamber 2 and which when opened will allow flow of paint into this pumping chamber.

The outlet check valve 6 as shown includes a spring pressed ball 41 cooperating with a seat 42.

The casing 30 has a passage 43 from the pumping chamber to the spring pressed ball 41.

The pump casing part 31 shown in FIG. 7 has a recess 44 in the face thereof mating with the casing half 30 and this recess receives a diaphragm support plate as hereinafter described.

The cylinder bore 13 receiving the piston 14 is lined with a sleeve 45 slidably supporting the piston which is in the form of a hollow cup 46, the closed or head end of which has a projecting nose 46a for engaging the wobble plate 15 and the hollow interior 46b of which receives a spring 47 bottomed at one end against a plastic spacer 48 seated against the head and at the other end against a metal spring retaining collar 49 held in abutted relation against the end of the sleeve 45 by a fastener 50 threaded into the casing 31.

The piston cup 46 has a groove 51 around the periphery thereof and holes 52 through the bottom of the groove connect the groove to the interior of the cup 46b. The cylinder sleeve 45 has holes 53 at spaced intervals therearound adapted to register with the groove 51 when the piston reaches the end of its suction stroke as above described. These holes 53 through the sleeve 45 communicate with the refill slot 21 decribed above and the refill passage 20 to the container 17. A cylindrical filter screen 54 is provided in the passage 20 and may conveniently be carried in a casing 55 threaded into the casing part 31 and easily removed therefrom for cleaning.

The container 17 shown in FIG. 17 is defined by an integral cylindrical wall 31a of the casing part 31. The overflow passage 18 as shown in FIG. 7 is provided by two drilled holes in the casing connected through a well 56 receiving the spring loaded needle valve 19 described above.

As shown in FIG. 8, the diaphragm 10 is a molded plastic unit 57 having a thick rigid central portion 57a surrounded by a thin flexible peripheral membrane portion 57b. A cylindrical stem 57c extends from the center of the thick portion 57a and has a threaded end 58. One face of the thick portion 57a is stepped to mate with the step portion 33a on the inner periphery of the insert ring 33 shown in FIG. 6. The opposite face of this central portion 57a is contoured to mate with the face of a metal backup or support plate ring 59 which in turn is seated in and mates with the recess 44 of the casing part 31 shown in FIG. 7. This support plate 59 has a central aperture 59a slidably receiving the stem 57c therethrough and this aperture 59a is surrounded by a ring of apertures 59b as shown in FIG. 9 for passage of driving liquid through the support plate 59.

As shown in FIG. 8, a coil spring 60 surrounds the stem 57c and a nut 61 threaded on the end 58 of the stem compresses the spring 60 against the support plate 59, thereby drawing the diaphragm 57 into seated relation on this support plate.

As shown in FIG. 5, the stem 57a and spring 60 extend into the spring 47 in the cup portion 46b of the piston. In this manner, the piston is biased against the wobble plate 15 while the diaphragm is biased against the support plate 59. The diaphragm 10 is thus always biased away from the insert ring 33.

The motor 16, as illustrated in FIG. 5, is in the form of an electric motor 62 driving a shaft 63 on which is keyed a flywheel 64 in the container 17. A thrust bearing 65 rotatably supports the flywheel 64 in the container and the wobble plate 15 is mounted in angled relation on this flywheel through radial bearing 66 and thrust bearing 67. A seal 68 is provided around the shaft 63 to stop leakage between the motor and container 17.

When the motor is driven to rotate the wobble plate 15, the piston 14 will be moved forwardly from its rearmost position shown in FIG. 5 against the bias of the spring 47 and will act through the driving liquid to force the diaphragm 10 off of the seating plate 59. The forward movement of the diaphragm in the pumping chamber 2 will discharge paint from the pumping chamber past the check valve 6 to the spray-gun outlet. Then, on the return stroke the diaphragm 10 will be biased back to the position shown in FIG. 5 enlarging the pumping chamber 2 and drawing paint from the inlet 4 through the inlet valve 5. The load of the spring 38 on this inlet valve 5 is such that the valve will not open on the initial retraction of the diaphragm so that the pumping chamber 2 is never filled with a liquid material and the dead space D will be preserved. The contour 33b of the insert ring 33 and the thin membrane portion 57b overlying this contoured portion cooperate with the spring load on the inlet valve to maintain this small dead space D.

In one commercial embodiment of a diaphragm pump for airless spray painting usage according to this invention, the pump chamber 2 of the pump has a capacity of about 19 cc., the outlet check valve 6 is spring loaded at about 150 grams with the spring having a rate of 60 grams/m.m. and the inlet valve 5 is spring loaded at about 300 grams with a spring rate of 75 grams/mm. The diaphragm 10 is spring biased into the chamber 11 by spring 60 at 23.4 kilgrams with a rate of 2.93 kg/m.m. When the relief valve 19 is set to open at 240 kg, this pump will deliver a pressure of about 150 kg/cc 2 to a spray-gun 8 having a delivery orifice diameter of 0.31 inches. The relief valve 19 may be varied to open at different pressures with a resultant variation in delivery pressure. The orifice size on the spray-gun 8 may be changed to vary the delivery pressure at the same relief valve setting. The piston 14 has a stroke of about 8 m.m. and the wobble plate 15 is driven at about 1,480 RPM. When such a pump is fully throttled to stop flow from the pumping chamber 2, the amount of driving fluid released through the valve 19 will not be more than about 6 percent of the volume of driving liquid in the chamber 11. Then, when the spray-gun 8 is opened for full delivery, the driving liquid will be replenished through the passage 20 at the rate of about 0.45 c.c. on each stroke of the piston 14 until the chamber is again filled with the driving liquid and the gate is re-dissolved in this liquid. The wobble plate drive has a wide speed range and is driven slow enough so that the piston cannot retract at a faster rate than the gas can be released.

It should be understood that the pump form of FIGS. 5 through 9 represents only one embodiment of the pump of this invention, and details of construction may be widely varied from this illustrated form without departing from the principles and scope of this invention.

It should be understood that the herein described diaphragm is a preferred fluid propelling member but it could be replaced with a piston, a bellows or the like fluid propelling device without departing from the principles and scope of this invention.

It should be understood that while the invention is particularly described as embodied in a pump, the principles of the invention are generally useful in fluid power transfer machines including motors as well as fluid propelling machines and such usage is included within the scope of this invention.