WO1987005973A1

WO1987005973A1 - Anti-contamination flow control in liquids

Info

Publication number: WO1987005973A1
Application number: PCT/AU1987/000078
Authority: WO
Inventors: Wlodzimierz Rast
Original assignee: W. Rast Pty. Ltd.
Priority date: 1986-03-20
Filing date: 1987-03-20
Publication date: 1987-10-08
Also published as: EP0261180A4; DE3773098D1; AU596169B2; JPS63503237A; EP0261180B1; EP0261180A1; AU7203787A; ATE67561T1

Abstract

A method of and means for anti-contamination flow control in liquids in a system using a motor unit (1) adapted to be driven by a pressure liquid having its drive coupled to drive a pump unit (6) adapted to pump liquid under pressure to a consumer device (9), in which the liquid is discharged from the motor unit (1) through an air gap (4), and collected from the air gap (4) by the pump unit (6) whereby to continue flow of pressure liquid beyond the air gap (4) to the consumer device (9).

Description

"ANTI-CONTAMINATION FLOW CONTROL IN LIQUIDS"

This invention relates to a method of and means for preventing contamination in liquids flowing from a mains to a consumer device.

As a prior art reference, the specification of 5. United States Patent No. 4, 297,086 of Peter T. McGowan, assigned to The Garrett Corporation, is cited, which uses a first pump unit which acts as a motor unit is driven by a first pressure fluid, is coupled to drive a second pump unit which acts as a slave unit, which 10. second pump unit pressurises a second fluid system.

In that system, as the first pump unit of a first fluid system, the second pump unit is mechanically driven by the first pump unit and serves as a means of presurising the fluid of the second system.

15. The cited United States Patent refers to transfer¬ ring hydraulic power from one system to another.

Where only a single system is used to drive a consumer device, where pressure liquids flowing from a supply line require to terminate in a consumer device

20. such as a washing machine or the like where pressure fluid is required, a serious problem exists, there being danger that the liquid can be contaminated if liquid flow back into the supply line occurs. This readily happens when back-syphoning occurs, such as when

25. the pressure in the supply main ceases or is reduced. It is the object according to my invention to prevent back-flow in such a hydraulic system.

According to this invention the problem is solved by having an air gap in the pressure line between the 5. source of supply and the consumer device, the device of the invention being so arranged that no external pressure is required on the receiver side of the device to which the supply is taken, but the pressure is maintained on the consumer side by means on the supply side which act- 10. uate a pump to maintain the pressure at about the same level as the supply line.

This is achieved according to the invention by having a primary pump unit at the terminal end of the pressure line which is driven by liquid flow, the liquid being dis-

15. charged from this primary pump unit by free fall into a funnel or receiving means to be pumped from this to the consumer line by a secondary pump unit in the consumer line. The primary pump unit and the secondary pump unit are coupled to be driven simultaneously and both are

20. arranged to have as near as possible the same volummetric flow.

The primary pump unit is of a positive type so that it acts as a valve in the line when the primary pump unit is inoperative and if the secondary pump unit is main- 25. tained stationary no flow from the pressure line takes place from the primary pump unit to the reservoir or fun¬ nel. When however the consumer device is actuated, the secondary pump unit is free to operate and allows the primary pump unit to be driven by the pressure liquid, to discharge the liquid into the reservoir through the air gap which is simultaneously taken up by the secondary 5. pump unit under drive of the primary pump unit to dis¬ charge to the consumer device. If the consumer device flow is cut off the secondary pump unit stops and, as the primary pump unit is coupled to it, it also stops and flow of the liquid from the mains to the pump unit 10. and from the delivery unit to the consumer device stops.

The main object of the present invention thus is to achieve a highly effective method of operation of such a device, a further object being a form of construction which is both simple and effective and which if desired 15. can also act as a meter to meter the fluid being used, the later of course being an optional feature.

The method according to this invention comprises caus¬ ing flow of pressure liquid through a primary pump unit adapted to be driven by a pressure fluid having its drive

20. coupled to the drive of a secondary pump unit adapted to pump liquid under pressure to a consumer device, dis¬ charging the liquid from the primary pump unit through an air gap, and receiving the liquid discharged from the air gap by the secondary pump unit (6) whereby to continue

25. flow of the pressure liquid beyond the air gap to the consumer device. The apparatus comprises a primary pump unit to receive a pressure fluid and be driven thereby, means to discharge the fluid from the primary pump to a vessel through an air gap, means to couple the drive of the primary pump 5. unit to the drive of a secondary pump unit, the second pump unit drawing liquid from the vessel and pressurizing it into a flow line by reason of the drive of the second pump unit from the drive of the first pump unit.

The pump units can take various forms but have similar 10. capacities so that pressure liquid flowing through the gap flows on beyond the gap at the same relative pressure by means of the arrangement. When flow from the secondary pump unit is stopped, the secondary pump unit and the primary pump unit both stop because they are coupled to- 15. gether drive-wise but immediately the consumer device draws pressure liquid from the secondary pump unit the first pump unit is caused to supply the liquid through the gap in the same proportion as the liquid is used by the consumer device.

20. According to a preferred form of the present invention two pairs of cylinders are formed in a housing, the one pair of cylinders being the primary pump unit, having two cylinders, which may be of unequal diameter, in each of which is a piston coupled by a connecting rod to a

25. piston in the secondary pump unit so that a first piston in the primary pump unit drives a first piston in the secondary pump unit for synchronised operation, while a second piston in the primary pump unit drives a second piston in the secondary pump unit.

30. Each of these pistons of the primary pump unit is coupled by means of a connecting rod to valve means which control the flow of liquid into the second piston of the primary pump unit but the out-flow of the primary pump unit is taken via an air gap to the input of the secondary pump unit so that, as the primary pump unit delivers liquid 5. as it is allowed to be driven as a motor by the pressure liquid from the supply line, it simultaneously activates the pistons of the second pump unit to receive the liquid from the pump unit and pressurizes it and pass it on to the consumer device. Because both pump units are coupled

10. together, that is the first and second pistons of the primary pump unit are coupled to the respective first and second pistons of the secondary pump unit, displacement occurring of the pistons in the primary pump unit are matched by displacment occurring of the pistons in the

15. secondary pump unit so that while there is an air gap between the two units, the liquid flows from the supply line through the primary pump unit then through an air gap, and is then available to the secondary pump unit which maintains the pressure in the on-flowing liquid

20. because of the drive coupling of the primary and secondary units.

In order however that the nature of the invention will be fully appreciated, embodiments thereof will now be described with reference to the accompanying drawings 25. which are by way of example only as the primary and second¬ ary pump units can take various form.

In the drawings,

FIG. 1 is a flow diagram showing a primary pump unit and a secondary pump unit with a secondary pump unit driven 30. by the primary pump unit through a drive coupler, showing the air gap and vessel which forms the anti-contamination device in that it prevents back flow of liquid from the secondary pump unit to the primary pump unit,

FIG. 2 is a somewhat schematic sectional side ele¬ vation of a typical pump assembly comprising both a primary 5. pump and a secondary pump with each divided into two com¬ ponents, using pairs of pistons and cylinders with the pistons of each pair actuated successively,

FIG. 3 is a similar view to FIG. 2 but showing in modified form using two pistons and a single cylinder 10. for the primary pump unit and similarly for the secondary pump unit, so that the cylinders of each pair of co¬ extensive and the pistons therein operate in a common chamber,

FIGS. 4 and 5 are isometric views of a vertical and 15. horizonal arrangement respectively of the unit shown in FIG. 3.

FIG. 6 is a view similar to FIG. 3 but showing a single cylinder version, and showing also a replenisher arrangement for ensuring correct liquid flow control 20. should the liquid level in the receiving means vary from a selected volume, and showing also a shut-off device to be actuated when excess liquid accumulates in the receiving means. The flow of liquid in two extreme positions of the float of the replenisher being indicated at A and B.

25. Referring first to FIG. 1, which demonstrates the general principle, pressure liquid is fed to the primary pump unit 1 by a pressure line 2 and drives the primary pump unit, the liquid leaving the primary pump unit 1 through the discharge line 3 under low pressure from whence it flows through the air gap 4 to receiving means 5 such as a vessel when the primary pump unit 1 is driven by the pressure liquid.

5. The secondary pump unit 6 has its drive connected by a drive coupler 7 to the drive of the first pump unit 1 so that the primary and secondary pump units 1 and 6 are driven synchronously. The pressure liquid outlet from the secondary pump unit 6 is taken by the pressure line 8 10. to the consumer device 9.

In operation, when the consumer device 9 accepts pressure liquid, the secondary pump unit 6 is free to rotate and this allows the primary pump unit 1 to be driven by the pressure liquid connected to the primary 15. pump unit 1.

As the two pump units 1 and 6 are coupled, the pressure in the outlet line 8 for the liquid is similar to the pressure in the inlet line 2.

There is however no direct fluid connection between 20. the inflow pressure liquid line 2 and the outflow pressure liquid line 8 because of the interposed air gap 4.

Referring now to FIG. 2, which describes a piston type unit, to which the invention need however not be limited, the first and second cylinders 10 and 11 of the pump unit

25. 1 communicate with a valve chest 12 which has a series of ports in it connected to the IN pressure line 2 from the pressure supply and the discharge line 3 from the unit to the air gap 4. These ports are controlled by valves 13 and 14 shown as slide valves, one actuated by a first

30. piston 15 of the primary pump unit 1 and the other by a second piston 16 of the primary pump unit 1 in such a way that when the first piston 15 of the primary pump unit 1 is displaced by fluid, the valve 13 is moved when the piston reaches near the end of the stroke of that first 5. piston 15 to change the flow through the porting of the valve chest 14, the pressure liquid driving the first piston 15 forward to near the end of the stroke whereupon the slide valve 13 coupled to it moves to change the porting to apply the pressure to the second piston 16 of

10. the primary pump unit 1 to drive that piston 16 to the opposite end of its stroke. As the second piston 16 nears the opposite end of its stroke the valve 14, connected to it in the chest 12 is actuated to again establish the first described state- and the first piston 15 is driven in

15. the opposite direction until it reaches near the end of its stroke whereupon the valve 13 coupled to it is again repositioned to actuate the second piston 16 of the primary pump unit 1.

The arrangement of the secondary pump unit 6 is sim- 20. ilar to that of the primary pump unit 1 and has a liquid inlet 17 and is arranged so that alternately the two pis¬ tons 18 and 19 of the secondary pump unit supply the liqu¬ id pumping action. The first and second pistons 18 and 19 of the secondary pump unit 6 act in cylinders 29 and 25. 30.

The sequence of the pistons 18 and 19 is so arranged that when the first piston 18 is on a delivery stroke the other piston 19 of the unit is stationary but as the first piston 18 reaches the end portion of its delivery 30. stroke the valve 20 in the valve chest 21 is changed to drive the second piston 19 on its stroke, the first piston 18 of the unit having reached the end of its stroke re¬ maining there and cutting off flow until the second piston

19 reaches the end portion of its stroke whereupon the valve 22 in the valve chest 21 is changed and the first

5. piston 18 is actuated on its next delivery stroke.

The first piston 15 of the primary pump unit 1 and the first piston 18 of the secondary pump unit 6 are con¬ nected to move in unison by a drive coupler 7, this being in the nature of a piston rod 23, the second piston 16 10. of the primary pump unit 8 and the second piston 19 of the secondary pump unit are similarly connected to move in unison by a piston rod 24.

The valves 20 and 22 of the valve chest 21 are con¬ nected respectively to the piston rods 23 and 24, as are 15. the valves 13 and 14.

The stems 25 of each of the valves 13, 14, 20 and 22 are connected to be actuated by stops 27 in the piston rods 23 and 24 but have interposed springs 28.

The first cylinder is designated 29 and the second 20. cylinder 30 and house the pistons 18 and 19 respectively.

If desired one of the pistons 15 or 16 of the primary pump unit 1 may be the main driving piston of the primary pump unit and can be of a substantial diameter, the second piston being of a smaller diameter as its function is 25. essentially to take over the pumping action as the first piston nears the end of its stroke and continues the pump¬ ing action while the first piston rests until the second piston reaches near the end of its stroke and the valve is changed over whereupon the first piston is driven in 5. the opposite direction, this arrangement ensuring a contin¬ uous flow of liquid and doing away with problems such as water hammer which is one of the basic problems with the mechanisms of this type.

Referring to the modified form shown in FIG. 3, in 10. which similar references are used for corresponding parts, the primary pump unit cylinders 10 and 11 and the second¬ ary pump unit cylinders are coaxial and the cylinders 10 and 11 form a common chamber as do the cylinders 29 and 30. The pistons 15 and 16 of the primary pump unit 1 and 15. the pistons 29 and 30 of the secondary pump unit 6 dividing the cylinders into their two active areas.

The action however is still similar to the form first described but it will be noted that as the piston rods 23 and 24 are coaxial, the rod 24 is hollow and has a 20. cut-away 33 to give access to the stops 27 on the piston rod 23.

The piston rod 23 actuates the valves 13 and 20 of the primary and secondary pump units 1 and 6 respectively through a rocker arm 34 which has an intermediate pivot 25. 35 connecting it to a frame not shown, which also carries the cylinders 10, 11, 29 and 30, the rocker arm being actuated by the stops 27 on the piston rod 23.

The rocker arm 36 is similarly carried by a pivot 37 to engage the valve stem 25 of the valves 14 and 22 to 30. activate these valves from the piston rod 24. The operation of the primary pump unit 1 is as follows:-

The primary pump unit 1 with the valves 13 and 14 in the position shown in FIG 3, causes pressure liquid

5. to flow into the port A and the liquid moves piston 15 down, expelling liquid through the port B and valve 13 into air gap 4 outlet.

At the end of the stroke of the piston 15, the valve 14 is moved to cover the port C and uncover the

10. port B. Mains pressure is maintained through the port A on the piston 15. Mains liquid then flows through the port B and moves the piston 16 down, expelling liquid through the port C to the valve 13 and then to the air gap 4 outlet. At end of the stroke of the

15. piston 16 the valve 14 is moved to cover the port A, thus allowing.pressure liquid to flow through the port B and move the piston 15 upwards, expelling liquid through the port A and valve 14 to the air gap 4 outlet. At the end of the stroke of the piston 15, the

20. valve 13 is moved to cover the port B and uncover the port C, allowing pressure liquid to flow through the port C, moving the piston 15 upwards and expelling liquid through the port B to the valve 13 and air gap 4 outlet. At completion of the upstroke of the piston

25. 16, the valve 14 is moved to uncover the port A, completing the cycle of the unit.

The operation of the secondary pump unit 6 is as follows:-

This unit operates in direct sequence with the primary pump unit 1. As the piston 18 is moved down by the piston 15, liquid is expelled through the port F and valve 22 to the consumer outlet 8. As this pis¬ ton 18 moves down, liquid is drawn in from the 5. receiving means 5 via the port E and valve 20. The valve 20 is moved upwards. The piston 19 moves down expelling liquid through port E to the outlet 8. Liquid is drawn in through the valve 20 and port D to the topside of the piston 19. The valve 22 is moved

10. upwards. As the piston 18 moves upwards, liquid is expelled through the port E and valve 20 to the consumer outlet 8. Liquid is drawn in through valve 22 and port F to the underside of piston 19. The valve 20 is moved down. The piston 19 is moved upwards,

15. expelling liquid through the port D and valve 20 to the consumer outlet 8. The underside of the piston 19 draws liquid in through the valve 20 and port E. The valve 22 is moved downwards. This completes the cycle of the secondary pump unit 6 at the same time as the primary

20. pump unit 1.

It will be realised that whatever water or other liquid passes through the primary pump unit 1 will be taken up through the air gap 4 by the secondary pump unit, and the liquid will be pumped by the secondary pump unit 6

25. to the consumer device 9 at a pressure substantially that of the supply means pressure because both units are con¬ nected to operate synchronously, so that while the stream of liquid is interrupted by the air gap 4, the pressure liquid on the IN side of the primary pump unit 1 drives

30. that pump unit to actuate the secondary pump unit 6 to maintain the same substantial pressure on the consumer side of the line.

In FIG. 2 a mechanical meter 40 is shown to record volume of water or other liquid used. In the form illustrated in FIG. 6, where again similar numerals are used for corresponding ports, only a single cylinder 10 and piston 15 is used as the primary pump unit 1, and similarly a single cy- 5. linder 29 and piston 18 is used as the secondary pump unit 6.

The valve 14 of the primary pump unit 1 is similar to that of the earlier described embodiment but no second valve corresponding to the valve 15 is required.

10. The valves 42 on the inlet side of the cylinder

29 of the secondary pump unit 6 are one-way valves, and similarly the valves 43 on the outlet side of the cylinder 29 are one-way valves.

An accumulator 44 is used to limit pulsing of 15. the liquid during flow changeover.

The replenisher device comprises a valve 45 in a valve chest 46, and this valve is activated through a rod 38 by a float 39 in the receiving means 5.

20. The port G of the valve chest 12 communicates with one end of the cylinder 10, but the port G also is connected through a one-way valve 41 with the port H of the valve chest 46.

The port J of the valve chest 12 communicates 25. with the other end of the cylinder 10 but also with the port K of the valve chest 46. The outlet port L of the valve chest 46 com¬ municates with a smaller auxilliary cylinder 47 having a piston 48 in it connected to the rod 23 of the piston 15, this piston being in its cylinder 47 only 5. through part of its stroke, the cylinder 47 opening to the cylinder 10. The port L is connected to the port K by a one-way valve 49.

The rod 25 of the valve 14 is actuated by an over balancing arm 50 which is held by a compression 10. spring 51 but over balanced by stops 52 on an actu¬ ating arm 53 secured to the rod 23 of the piston 15.

The inlet 2 to the valve chest 12 has a stop cock 54 in it connected by a rod 55 to a pivoted 15 latch arm 56 loaded by a spring 57 and normally retain¬ ed by a pivoted latch 58 which is released from the latch arm 56 when the weight of liquid in the receiv¬ ing means exceeds a calculated amount.

The latch arm is actuated by a cam 59. A spring 20. 60 serves to control the position of the receiving unit 5 about a fulcrum 61.

The operation of the replenishing system, which is designed to maintain the liquid level at a correct value is as follows:-

25. The valve 45 is controlled by the float 39 so that when the liquid level in the receiving means 5 drops, the valve 45 moves to join the ports K and L. When the piston 15 moves upwards and the valve 14 is down, liquid is expelled through the port J to the air gap 4 as normal. As the auxiliary piston 48 enter its smaller cylinder 47, liquid is expelled through 5. the port L to the valve 45, then through the port K to the valve 14 and the air gap 4 outlet. This liquid from the small cylinder 47 raises the level in the receiving means 5 until the float 39 changes the valve 45 to the by-pass position.

10. When the receiving means 5 is filled to correct level, the ports L and H arc connected, K¹ is dis¬ connected. As the pistons 15 and 48 move upwards, the liquid in the small cylinder 47 is expelled thro¬ ugh the port L by piston 48 to the valve chest 46

15. and through the port H to the port G and the underside of the piston 15. This liquid is by-passed from the small cylinder 47 to the main cylinder 15 and is at a higher pressure, as the piston 15 is of larger area than piston 48.

20. The above action can be seen to comprise measur¬ ing the relative volumes of liquid in the primary pump unit 1 and the secondary pump unit 6, and regul¬ ating the volume in the primary pump unit 1 by a float valve 49 to control the pressure liquid flow

25. to the primary pump unit 1.

The mains cut-off system is designed to prevent overflow of the receiving means 5 and thus to prevent flooding and acts as follows:- The receiving means 5 is connected to a support by a pivot which acts as a fulcrum 61 and is pivotted off-centre and balanced by a spring 60 to be level when the liquid is at operation level. In the case 5. of line breakage or seal damage, the level in the receiving unit 5 rises, and the receiving unit tips on the fulcrum 61 to cause the face of the cam 59 to release a spring loaded latch arm 56 which closes the stop-cock 54, cutting off the liquid supply.

10. To reset, the liquid level in the receiving unit 5 is lowered and the mechanism reset to the normal position ready to be tripped at the next mal¬ function.

The operation of the device which forms this invention 15. as described and illustrated with reference to the fore¬ going embodiments will be readily appreciated if it is realised that the primary pump unit 1 will have the pressure from the supply means on it at all times but can only operate when the pump unit is free to move, because 20. the driven means are coupled on an equal-capacity basis to the driven means of the secondary pump unit 6 so that if there is no outflow from the secondary pump unit 6 to the consumer device 9 that unit is locked and holds the driven means of the primary pump unit similarly locked. While 25. the drive for the whole unit comes from the pressure exerted on the primary pump unit 1, the control of flow is by the consumer device 9 which controls the output of the secondary pump unit 6.

By using positive displacement means for the pump 30. unit and the delivery unit it will be realised that at the consumer end the effect is as though there is a direct pressure line connection between the supply line and the consumer device but because of the air gap no back flow can take place through the unit so that there is no risk 5. of contamination as the consumer device can not feed back liquid to the mains as such flow could not take place across the air gap.

It will be realised that other forms of the device using vanes instead of pistons or other types of liquid

10. pumps can be used to achieve the objective, but the form of unit illustrated is, because of its positive displace¬ ment and relative simplicity of construction, suited to most purposes and by selecting correct volummetric dimen¬ sions the pistons can be caused to operate relatively

15. slowly under normal conditions therefore greatly reducing wear and in the case of the liquid being water the con¬ struction can be at least in part of plastics which are water lubricated to ensure the reduction of wear and cor¬ rectness of operation.

20. The valves of course can be other than slide valves provided they control the liquid flow and in this respect it is also important to appreciate as previously stated that while the one piston is on a power stroke the other piston is at rest until the first piston reaches near the

25. end of its stroke whereupon the other piston takes over the displacement while the first piston stops at the end of its stroke and remains there until the second piston is near the end of its stroke whereupon the valves reverse flow and as the second piston readies the end of its stro-

30. ke, the other piston is already on its power stroke, there¬ by giving continuous flow without any interruption.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method of anti-contamination flow control in liquids in a system using a primary pump unit (1) adapted to be driven by a pressure liquid having its drive (7) coupled to drive a secondary pump unit (6)

5. adapted to pump liquid under pressure to a consumer device (9), characterised by discharging the liquid from the primary pump unit (1) through an air gap (4), and receiving the liquid from the air gap (4) at the secondary pump unit (6) whereby to continue flow of 10. pressure liquid beyond the air gap (4) to the consumer device (9) .

2. The method of claim 1 characterised in that the air gap (4) is disposed between a discharge line from the primary pump unit (1) and receiving means (5) , characterised by drawing the liquid from the receiving

5. means into the secondary pump unit (6).

3. The method of claim 1 or 2 characterised by measuring the relative volume of liquid in the primary pump unit (1) and the secondary pump unit (6), and regulating the volume of liquid in the primary pump unit

5. (1) by control by float means at the receiving means (5) of the pressure liquid flow to the primary pump unit (1).

4. The method of claim 1, 2 or 3 characterised in that the primary pump unit (1) comprises at least a piston (15) in a main cylinder (10) and valve means (13,14), and the secondary pump means (6) also comprises

5. at least a piston (18) and valve means (20,22), feeding pressure liquid to the valve means (13,14) of the primary pump unit (1) from a pressure line (2) and allowing the liquid to discharge from the primary pump unit (1) into an air gap (4), receiving the liquid from

10. the air gap (4) and pressurising it in the secondary pump means (6) to supply pressurised liquid at the consumer device (9) whereby the flow of liquid through the primary pump unit (1) is synchronised with the flow of liquid through the secondary pump unit (6) by the

15. drive couplings between the primary pump unit (1) and the secondary pump unit (6).

5. The method of claim 3 wherein the primary pump unit (1) contains two pump means (10,11) arranged as a pair and the secondary pump unit also contains two pump means (29,30) arranged as a pair, characterised by

5. alternately but synchronously activating the two pump means (10,11,29,30).

6. The method of claim 4 or 5 characterised by activating liquid replenisher means which comprises coupling a smaller capacity auxiliary cylinder (47) to communicate with a main cylinder (10) of the primary

5. pump unit (1), said auxiliary cylinder (47) having a piston (48) therein connected to the piston (15) of the main cylinder, causing liquid flow to and from the said cylinders (10,47) when the pistons (15 and 48) therein are driven by pressure fluid, adding fluid from the 10. pressure supply to the cylinders (10,47) when a float valve (47) is actuated by a drop in the level of liquid in the receiving means (5) whereby to balance the volume of liquid in the primary pump unit (1) with liquid in the secondary pump unit. 7. The method of any preceding claim characterised by the stops of measuring the liquid in the receiving means (5), and causing the flow of liquid to the primary pump unit (1) to cease when the receiving means (5) 5. reach a predetermined volume.

8. Apparatus for anti-contamination flow control in liquids in which a primary pump unit (1), arranged to be driven by pressure liquid, has its drive coupled to drive a secondary pump unit arranged to deliver the

5. pressure fluid to a consumer device (9), characterised by an air gap (4) disposed between a liquid outlet (3) of the primary pump unit (1) and a liquid inlet (17) of the secondary pump unit (6).

9. Apparatus according to claim 8 characterised in that the primary pump means (1) and the secondary pump means (6) each have positive liquid displacement means coupled to cause the displacement means of the

5. primary pump unit (1) to synchronously drive the dis¬ placement means of the secondary pump unit (6).

10. Apparatus according to claim 8 further char¬ acterised by at least a first main piston (15) in a cylinder (10) adapted to be driven through valve means (12,14) by pressure liquid from a pressure line (2) to

5_, form the primary pump unit (1) to deliver liquid through a discharge line (3), at least a first main piston (18) in a cylinder (29) adapted to act through valve means (20,22) as a pump for liquid to form the secondary pump unit (6) to deliver liquid to the consumer device (9),

10. drive coupling means (23) between the piston (15) of the primary pump unit (1) and the piston (18) to cause synchronous actuation of the pistons (15 and 18), said air gap (4) being positioned between said discharge line (3) of the primary pump unit (1) and receiving means (5)

15. discharging to the valve means (20,22) of the secondary pump means (6) .

11. Apparatus according to claim 8 further char¬ acterised by a first main piston (15) and a second piston (16) in first and second cylinders (10,11) in the primary pump unit (1) to form a pair, and a first main 5. piston (18) and a second piston (19) in first and second cylinders (29,30) in the secondary pump unit (6) to also form a pair, a first piston rod (23) coupling the first main piston (15) of the primary pump unit (1) to the first main piston (18) of the secondary pump unit (6), a

10. second piston rod (24) coupling the second piston (16) of the primary pump unit (1) to the second piston (19) of the secondary pump unit (6), means (34) coupling the first piston rod (23) to the valves (13,20), means (36) coupling the second piston rod (24) to the valves

15. (14,22), said couplings being arranged to cause said pistons to be driven alternately.

12. Apparatus according to claim 11 further char¬ acterised by stops (27) on the said first piston rod (23) and the second piston rod (24) positioned to engage the means (34,36) which actuate the valves (13,20 and

5, 14,22) near the end of the stroke of the pistons (15,16 and 18,19) whereby as a piston nears the end of its stroke the valves (13,20 or 14,22) are actuated to cause the other piston of each pair to be actuated.

13. Apparatus according to claim 11 or 12 wherein the first cylinders (10,29) of the primary and secondary pump units (1,6) are coaxial and the second cylinders (11,30) of the primary and secondary pump units (1,6)

5_Φ are coaxial.

14. Apparatus according to claim 12 wherein all the cylinders (10,11,29,30) are coaxial, the cylinders (10,11) of the primary pump unit (1) are co-extensive and, the cylinders (29,30) of the secondary pump unit

5. (6) are co-extensive, whereby the pistons (15,16) of the primary pump unit (1) are positioned in a common chamber and the pistons (18,19) of the secondary pump unit (6) are also positioned in a common chamber.

15. Apparatus according to claim 8 further char¬ acterised by: a main cylinder (10) having a piston (15) therein forming with valve means (14) the said primary pump unit (1), a main cylinder (29) having a

5. piston (18) therein forming with valve means (42,43) the said secondary pump unit (6), said cylinders being spaced apart but coaxial, a piston rod connecting the piston (15) of the primary pump unit (1) to the piston (18) of the secondary pump unit, valve means (14) arr-

10. anged to alternately connect pressure liquid to the two ends of the cylinder (10) of the first pump unit (1) and discharge liquid to an air gap (4), valve means (42,43) arranged to alternately direct liquid from the air gap (4) to the two ends of the cylinder (29) and

15. discharge pressure liquid to the line (8) to the con¬ sumer device, further characterised in that the valve means (14) of the primary pump unit (1) are actuated by stops (52) on an actuating arm (53) on the piston rod (23), and the valves (42,43) are pressure actuated one-

20. way valves.

16. Apparatus according to claim 15 further char¬ acterised in that the stops (52) on the piston rod (23) actuate a valve rod (25) of the valve (14) through an over balancing arm (50).

17. Apparatus according to claim 8 further char¬ acterised by replenishment means to maintain balance of the liquid in the primary pump unit (1) with liquid in the secondary pump unit (6) which means comprise:

5. an auxiliary cylinder (47) of lesser volume than the main cylinder (10) of the primary pump unit (1) and communicating therewith, a piston (48) in the auxiliary cylinder (47) coupled to the piston rod (23) of the piston (15) in the main cylinder (10), a valve (45) in a valve chest (46) coupled in one position to allow

10. pressure liquid to flow to the space between the closed end of the smaller cylinder (47) and the piston (48) therein while closing off flow from the opposite end of the main cylinder (10) whereby to add liquid to the primary pump unit, and means connecting the said valve

15. (45) in the valve chest (46) to a float (39) in a vessel forming the receiving means (5), whereby liquid is added to the secondary pump unit (6) when the level in the re¬ ceiving means falls below a selected volume.

18. Apparatus according to claim 10 further char¬ acterised by a stop-cock (54) in the pressure line (2) to the valve chest (12), means to measure the volume of liquid in the receiving means (5), and coupling means 5. (55) to close the stop-cock (54) when the volume of liquid exceeds a selected value.