GB2302712A

GB2302712A - Air-operated hydraulic motor

Info

Publication number: GB2302712A
Application number: GB9513284A
Authority: GB
Inventors: John Gerard Foster
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-06-29
Filing date: 1995-06-29
Publication date: 1997-01-29
Anticipated expiration: 2015-06-29
Also published as: GB2302712B; GB9513284D0

Abstract

In an air-operated hydraulic reciprocating pump comprising a pump piston (6) driven by an air motor piston (15), the reciprocation of the piston (15) is controlled by a control valve (20) and a spool valve (28), both disposed in the piston (15). Air for driving the motor piston (15) is supplied through an inlet (24) in a body (1) and enters an annular passage (14) around the piston (15). At the beginning of the pumping stroke air flows from the annular passage (14) through passages (26,33) and the valve (20) to cause rightward displacement of the spool (28). Thus air enters, via passages (26,26a,35), a chamber (36) in the body (1) to drive the pistons against the action of a spring (8). The return stroke occurs when the valve (20) is opened by its spindle (21) striking the body (1). This allows the air loading the large end (29) of the spool valve to flow out through an exhaust passage (9a). The consequential unbalancing of the spool valve causes it to return to its original position in which the chamber (36) is isolated from the air supply and is instead connected to atmosphere.

Description

FLUID PUMPS This invention relates to fluid pumps and more particularly to an improved air driven hydraulic pump.

Air driven hydraulic pumps are widely used in industry and have been available for many years. These pumps use the underlying principle that a large diameter piston driven by low pressure fluid can be used to generate higher pressure by moving a smaller diameter piston. The most common media used are low pressure air driving the low pressure stage and the high pressure stage generating pressure in hydraulic oil or water.

There are two basic types of air driven pumps, a single acting unit and double acting unit.

The single acting unit has air applied to only one side of a large diameter piston which actuates a smaller diameter piston rod as it moves, thus generating pressure. As the piston moves it also compresses a spring or stretches an extension spring so that at the limit of the piston stroke, means are required to shut off the air supply and to exhaust the chamber behind the low pressure piston to atmosphere to allow the compression spring to push the low pressure piston and high pressure piston rod back to a stop position which draws in more oil in the hydraulic section ready to start the next pressure stroke. At the end of the exhaust stroke, means are required to shut the flow path to atmosphere and then to reconnect the air supply.

It will be noted later that at least two low cost designs do not bother to shut off the air supply on the exhaust stroke although this inevitably wastes air. In principle, it can also be the case that the chamber is not vented to atmosphere, but is simply venting to a lower pressure.

In double acting pump units the means of switching air and exhaust is more complicated as the low pressure piston is driven by air pressure in either direction which means that the other side of the piston in each direction has to be connected to atmosphere to allow it to move.

Most designs of single and double acting pump units use some form of pilot valve to pneumatically actuate a spool which controls the air flow.

One disadvantage of such systems is that the control of air to the unit is complex and are thus expensive.

Another disadvantage is that the air piston strikes and actuates an air pilot valve at either end of its stroke. But in existing units air has to be routed to these valves which requires passages formed within the pump body casting or alternatively external pipework is provided for the air.

An aim of the present invention is to overcome the above mentioned disadvantages and provide an improved fluid pump with an integral low pressure large diameter piston and a high pressure smaller diameter piston generating pressure in a hydraulic fluid.

According to the present invention there is provided a fluid pump comprising a pump body having a chamber,an air piston assembly reciprocatable within the chamber, a piston having a smaller diameter end face than the air piston located between the air piston assembly and the pump body, the smaller piston being reciprocatable in a chamber in the pump body to pump a fluid into and out of the pump body, wherein the air piston incorporates a control valve in cooperation with a spool valve to pump air through the air piston to reciprocate the air piston within its chamber and to simultaneously reciprocate the smaller diameter fluid piston.

Conveniently, the air piston assembly is held at its reverse stroke by a compression spring encircling the fluid piston.

Preferably, the control valve comprises inlet and exhaust valves which are actuated by engagement with the pump body and end plate respectively.

The air piston assembly may include an annular chamber encircling the piston and cooperating with an air inlet in the air chamber wall.

Preferably, the spool valve has three ports for the inlet and operation of the spool valve within its chamber and an exhaust port connected to the outside of the pump body.

In an alternative construction the control valve may comprise two separate valve chambers with an inlet valve and an exhaust valve respectively, the valves being held on their respective seatings by spring loaded members.

The fluid pump barrel wall housing the air piston assembly may be formed with an annular air chamber to receive and supply air to the air piston.

This may comprise an outer plastics cylinder and an inner metal cylinder in which the air piston reciprocates, the inner and outer walls being sealed at their upper and lower ends to the pump body and base plate by plastics seals.

The annular chamber encircling the piston may be divided to form two annular chambers sealed from each other, one chamber being connected with an air inlet and the other chamber with an air outlet.

An embodiment of a fluid pump, according to the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is an axial cross-section of one embodiment of a fluid pump; Fig. 2 is a fragmentary section of one embodiment of a pilot valve; and Fig. 3 is a fragmentary axial cross-section of a modified air inlet of the fluid pump of Fig. 1.

The improved fluid pump illustrated is an hydraulic oil pump comprising a pump body 1 formed integrally with a central bearing 2, the body 1 extends downwards with an air barrel 3 and is closed at its base by a base plate 4. Slidably located within the air barrel 3 is an air piston assembly 5 the upper surface of which is engaged by a hydraulic piston rod 6 which is located in the bearing 2 and is sealed therein by a ring-seal 7. A compression spring 8 encircles the rod 6 and engages the upper surface of piston assembly 5 at its lower end and is located on bearing 2 at its upper end engaging the underside of the pump body 1. The compression spring serves to hold the piston assembly 5 away from the pump body 1 in the inoperative position.

The pump body 1 has a chamber 9 in which the piston rod 6 reciprocates, sucking oil into an inlet 10 past a spring loaded non-return ball valve 11 and plumping the oil through an outlet 12 also provided with a spring loaded non-return valve 13. Air from chamber 9 is exhausted to the atmosphere via an exhaust passage 9a.

The piston assembly 5 includes an annular passage 14 encircling the outside of a piston 15 which forms a fluid-tight seal with the air barrel 3 by two 'O'-rings 16 and 17 in respective grooves 18 and 19 in piston 15.

Incorporated within the piston 15 is an air control valve 20 having two spring loaded axial spindles 21 and 22. The spindle 21 connects the air valve 20 with an air chamber 23 at the top of the piston assembly 5 while the other spindle 22 controls the flow of air entering the pump through an inlet 24, formed in the air barrel 3 and is sealed in the piston 15 by an '0' ring seal 25.

The air inlet 24 is connected via the annular passage 14 with a passage 26 leading from the passage 14 to the lower spindle 22 leading to the air valve 20 and with a further passage 26a formed in the piston assembly with a chamber 27 housing a spool valve 28. The passage 26a may be drilled from the annular passage 14 direct to the spool chamber 27.

The spool valve 28 has an enlarged head 29 at one end sealed in the chamber 27 by an '0' ring seal 30 and a smaller head 31 at its other end also sealed in the chamber 27 by an '0' ring seal 32. The chamber 27 is connected at one end via the passage 33 with air valve 20 and at the other end via passage 34 with air chamber 9. A third passage 35 leads from the middle of spool valve 28 to an air chamber 36 below the piston assembly 5.

In operation as the piston rod 6 reciprocates in the pump body 1, oil is drawn in through inlet 10 past non-return valve 11 on the rear stroke of the rod and as the rod is pushed back into the bearing 2 pressure is generated to force the oil out past non-return valve 13 to the outlet 12.

The piston rod 6 is actuated by movement of the air piston assembly 5, which is moved by air acting on the pressure stroke on the full area of the piston at the base of the pump. The difference in area between the leading end of the hydraulic piston rod 6 and the surface of the lower end of piston 15 produces an intensification of the applied pressure such that low pressure air can generate high hydraulic pressure at the pump outlet.

During the pressure stroke of the piston assembly 5, the air piston 15 compresses the return spring 8 at the end of the pressure stroke and the spool valve 28 exhausts to atmosphere the volume of compressed air, driving the air piston 15 and the air piston moves back under the action of return spring 8 drawing in more oil through the non-return valve in the inlet 10 as piston 15 moves.

The valve 28 is a three port, two position spool valve actuated by means of the two air control valves 21 and 22. When the air piston moves on the pressure stroke air flows through the air barrel inlet port 24 and into the annular passage 14 encircling the air piston. Air from the passage 14 flows into the spool valve chamber 27 via passages 26 and 26a and into air chamber 36 below the air piston 15 corresponding to the full area of the piston.

At the end of the pressure stroke the spindle 21 strikes against the underside of the pump body 1 which opens the valve and instantaneously exhausts the chamber at the large head end of spool valve 28. The spool 28 then becomes unbalanced which causes it to move back, closing the path to the air pump and opening up a path from the pump chamber to the atmosphere. The air piston 15 then returns away from the hydraulic section under the action of the compression spring 8.

At the end of the exhaust stroke, the spindle 22 will strike against the base plate 4 and instantaneously the valve will be opened and air will move the spool 28 to open up the path from the air inlet to the pump chamber 9.

In a modification of the air pump the air inlet control valve is separated into two valves as shown in Fig. 2.

In this modified valve the air enters the piston assembly 5 through inlet 24 via a separate pressure valve 22a sealed in an '0' ring seal 25a and held in its closed position against a resilient seating 22b by a coil compression spring 22c.

Air from the pressure valve is led via passage 21f to a second valve 21 a which can be actuated to exhaust the air pressure. This valve is held in its closed position by a compression spring 21b against a resilient seating 21c..

In a further modification of the air pump as shown in Fig. 3 of the drawings, the pump body 1 is bolted by bolts 37 to a base plate 38. Between the pump body and base plate is located a cylindrical barrel member comprising an outer polyvinyl chloride (PVC) tube 39 spaced from an inner thin walled brass tube 40.

The air piston assembly 5 reciprocates in the brass tube 40 engaging the pump body and base plate at the ends of its strokes.

Interposed between the ends of the barrel tubes 39 and 40 are polyurethane gaskets 43 to seal the ends of the barrel and to form an annular air chamber 41 for air entering the chamber via an air inlet 42 in the pump body 1. An air inlet hole 42 is provided in the inner brass tube 40 to allow air to enter the control valves in the air piston assembly 5.

This modified construction provides a simple and inexpensive way of allowing inlet air to enter the air piston assembly. It is to be understood that Fig. 3 is a simplified diagram of the improved air pump and the other essential components are those described and illustrated in Fig. 1.

Various other modifications may be made to the improved air pump of the present invention. For example, the hydraulic piston rod is not rigidly attached to the air piston assembly to avoid any problem of dismantling and alignment during assembly of the air pump.

In a preferred construction the hydraulic piston rod is decoupled using a coiled compression spring engaging a loose washer at its lower end where it engages the air piston assembly, the lower end of the piston rod having a disc plate member which engages the upper surface of the air piston with the interposition of a buffer ring between the washer and disc plate.

A further modification is to provide a cushion between the base of the air piston and the base plate in the form of a buffer. This may be secured to the base of the air piston or to the base plate to cushion the impact of the piston as it moves towards the base plate on its exhaust stroke.

In another construction of the air pump the lower seal on the air piston is replaced with a strip of polytetrafluoroethylene (PTFR) bearing material or to remove the seal complete.

In some existing air pump designs the air supply is 'on' continually and the air is wasted on the exhaust stroke whereas the improved pump shuts off the air on the exhaust stroke.

Other modifications which may be incorporated in the improved air pump of the present invention include an air inlet tube through the base plate which is slidably engaged in the air piston to supply air to the air pump. The air may also be supplied through the base plate by a flexible tube connected with the base of the air piston.

Another arrangement would be to provide a fixed air inlet tube from the base plate to slidably engage the air piston and another tube from the pump body to slidably engage the air piston such that air is supplied in one tube and exhausted from the other tube. Independent inlet and exhaust tubes may be arranged side by side from the pump body to slidably engage the air piston for the supply and exhausting of air, this would permit double-acting operation.

Instead of one annular air supply chamber encircling the air piston, two annular chambers placed one above the other in the piston wall with ring seals to seal them from the barrel wall of the pump are provided. Air is supplied to one of the chambers while air is exhausted through the other chamber through an inlet and outlet respectively in the barrel wall of the pump. This would permit double-acting operation.

Claims

CLAIMS:

1. A fluid pump comprising a pump body having a chamber, an air piston assembly reciprocatable within the chamber, a piston having a smaller diameter end face than the air piston located between the air piston assembly and the pump body, the smaller piston being reciprocatable in a chamber in the pump body to pump a fluid into and out of the pump body, wherein the air piston incorporates a control valve in cooperation with a spool valve to pump air through the air piston to reciprocate the air piston within its chamber and to simultaneously reciprocate the smaller diameter fluid piston.

2. A fluid pump as claimed in Claim 1, wherein the air piston assembly is held at its reverse stroke by a compression spring encircling the fluid piston.

3. A fluid pump as claimed in Claim 1 or 2, wherein the control valve comprises inlet and exhaust valves which are activated by engagement with the pump body and end plate respectively.

4. A fluid pump as claimed in any preceding claim, wherein the air piston assembly includes an annular chamber encircling the piston and cooperating with an air inlet in the air chamber wall.

5. A fluid pump as claimed in any preceding claim, wherein the spool valve has three ports for the inlet and operation of the spool valve within its chamber and an exhaust port connected to the outside of the pump body.

6. A fluid pump as claimed in any preceding claim, wherein the control valve comprises two separate valve chambers with an inlet valve and an exhaust valve respectively, the valves being held on their respective seatings by spring loaded members.

7. A fluid pump as claimed in any preceding claim, wherein the fluid pump barrel wall, housing the air piston assembly, is formed with an annular air chamber to receive and supply air to the air piston.

8. A fluid pump as claimed in Claim 7, wherein the fluid pump barrel wall comprises another plastics cylinder and an inner metal cylinder in which the air piston reciprocates, the inner and outer walls being sealed at their upper and lower ends to the pump body and base plate by plastics seals.

9. A fluid pump substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

9. A fluid pump as claimed in Claim 8, wherein the annular chamber encircling the piston is divided to form two annular chambers sealed from each other, one chamber being connected with an air inlet and the other chamber with an air outlet.

10. A fluid pump substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

Amendments to the claims have been filed as follows 1. A fluid pump comprising a pump body having a chamber, an air piston assembly reciprocatable within the chamber, a piston having a smaller diameter end face than the air piston located between the air piston assembly and the pump body, the smaller piston being reciprocatable in a chamber in the pump body to pump a fluid into and out of the pump body, wherein the air piston incorporates a control valve in cooperation with a spool valve to pump air through the air piston to reciprocate the air piston within its chamber and to simultaneously reciprocate the smaller diameter fluid piston, the control valve comprising two separate valve chambers with an inlet valve and an exhaust valve respectively, the valves being held in their respective seatings by spring loaded members.

2. A fluid pump as claimed in Claim l, wherein the air pistoll assembly is held at its reverse stroke by a compression spring encircling the fluid pistol.

4 A fluid pump as claimed in any preceding claim, wherein the air piston assembly includes an annular chamber encircling tlle piston and cooperating with an air inlet in the air chamber wall.

5. A fluid pump as claimed in any preceding claim, wherein the spool valve has three ports for the inlet and operation of the spool valve within its chamber and an exhaust port collected to the outside of the pump body.

6 A fluid pump as claimed in ally preceding claim, wherein the fluid pump barrel wall, housing the air piston assembly, is fonned with an annular air clamber to receive and supply air to the air piston.

7. A fluid pump as claimed in Claim 6, wherein the fluid pump barrel wall comprises another plastics cylinder and an inner metal cylinder in which the air piston reciprocates, the inner and outer walls being sealed at their upper and lower ends to the pump body and base plate by plastics seals.

8. A fluid pump as claimed in Claim 7, wherein the annular chamber encircling the piston is divided to form two annular chambers sealed from each other, one chamber being connected with an air inlet and the other chamber with an air outlet.