GB2157778A - Fluid pumping systems - Google Patents

Abstract

The invention relates to a fluid pumping system wherein a number of pump units (1) are driven by a corresponding number of cams (14) on a common cam shaft (13). In such systems selective actuation of one or more of the units enables an individual pump unit to serve an individual end use, a number of units to be grouped to serve a common end use or all the units to be grouped to serve a single end use. Each unit comprises a piston (41) reciprocable in a respective cylinder (3) by the drive cam (3). Each cylinder has an inlet valve (18) and an outlet valve (37), the flow of fluid to the inlet valve being from an inlet (16) and a passage (15) when a respective fluid- operated valve (25) is open. Fluid pressure is admitted to an associated cylinder (33) containing an actuating piston (34, 30) for the valve (25). All of the fluid-operated valves are connected to a common control means operable to direct fluid to the cylinders of those units which are required to be operated. <IMAGE>

Description

SPECIFICATION Fluid pumping systems This invention relates to fluid pumping systems and is particularly concerned with pumping systems in which a number of pump units units are associated with and driven by number of cams on a common cam shaft.

Thus, it is known to provide number of pump units in side-by-side relationship, and where each unit has a piston which itself, or its piston rod, extends out of the unit and into contact with a respective cam on the cam shaft, the pressure in the fluid being pumped on a return spring acting on the end of the piston to cause the return stroke and maintain contact between the opposite end of the piston or the end of the piston rod, and the respective cam.

Each pump may deliver pressure fluid to a separate driven unit, or the outputs from several pumps may be collected to deliver pressure fluid to a driven unit. On other occasions, the outputs from all the pumps are collected to deliver pressure fluid to a single driven unit.

With such systems, it is frequently the case that where several driven units are involved, they need to be activated selectively, and when a single driven unit is involved, it frequently requires variation in its power supply.

This presents difficulties in pumping systems of the type under discussion, where some but not all pumps are required to be active and yet all pistons are driven by cams on a common drive shaft.

The object of the invention is to provide simple and efficient means of deactivating any one pump in a pumping system of the type under discussion.

According to the present invention, a pumping system comprises a number of pump units, each of which has a piston, which of itself or by a piston rod extends to respective drive cam, and where all the drive cams are on a common cam shaft, each pump unit having a fluid inlet, a line connecting the fluid inlet to a cylinder in which lies the piston, and a line connecting the cylinder to a valved fluid outlet, and there being in the line from the inlet to the cylinder, a first valve to isolate the cylinder from the inlet, and a second pilot valve to isolate the first valve from the inlet, all the said pilot valves being connected to a common control means, and whereby each pump unit or groups of pump units can be selectively activated.Preferably, both the first valve and pilot valve of each pump unit have a valve head spring loaded towards a valve seat, the spring loading on the valve head of each first valve being such that with the pilot valve closed, the pressure drop in the fluid in the line from the pilot valve to the first valve, allows the first valve to close, and with the pilot valve open, the pressure of fluid in that line overcomes the spring-loading to open the first valve and connect the pump cylinder to the fluid inlet.

The pilot valve of each pump unit may incorporate a stem contacting the valve head to the opposite side to the spring, the stem extending to a piston in a cylinder unit secured to the pump unit. Here, the cylinder unit may be connected to a control means in the form of a control valve to admit pressure fluid to the cyinder unit, to drive the piston along the cylinder and hence drive the stem against the pilot valve head, to open the pilot valve against its spring loading.

Thus, with all the pilot valves connected to a multi-position control valve, pressure fluid can selectively be delivered to activate the pilot valve of a single pump unit, a group of pump units or all the pump units as operating conditions may require.

One embodiment of the invention is illustrated in the accompanying drawing, which is a semi-schematic section through a pump unit controlled in accordance with the invention.

In the drawing, a pump unit 1 has a body member 2 formed with a blind bore to serve as a cylinder 3 for a piston 4 that extends as a sliding fit through a centre orifice 5 of a cap 6 closing the open end of the cylinder. Within the cylinder are a number of seals 7 surrounding the piston, compressed into sealing engagement with the outer face of the piston and the walls of the cylinder by a spring 8 and located at the closed end of the cylinder on a spigot member 9. To ensure that any pumped fluid that leaks past the seals 7 does not freely emerge outside the body, the cap 6 has an annular chamber 10 connected to a passageway 11 through the cap, leading to a drainage port 1 2 through the body.

Externally of the body, a cam shaft 1 3 is provided on which is mounted a cam 14 to act on the exposed end of the piston.

To one side of the body member 2 a fluid passageway 1 5 is provided, connecting a fluid inlet 1 6 to an inlet port 1 7 to the cylinder. In the passageway 15, a main inlet valve 1 8 is provided. Thus the body member has a blind bore 1 9 into which the passageway 1 5 emerges, with a valve seat 20 located in the end of the bore. The bore 1 9 is closed by a plug member 21, the stem 22 of which is counter bored to provide location for a spring 23 which acts on a valve member 24 to urge the valve member towards the valve seat 20.

Also in the passageway 15, and between the inlet 1 6 and the main inlet valve 18, is a pilot valve 25.

The body member 1 is provided with a blind bore 26, into which the inlet 1 6 emerges, and mounted in the bore 26 is a valve seat 27, below which is a valve member 28 urged towards the seat by a spring 29.

Extending along the bore 26 is a valve stem 30 slidably mounted on a closure plug 31 with a sealing ring 32 provided to prevent the egress of fluid. The stem 30 extends into a cylinder 33 mounted externally of the body member to be contacted by a piston 34, and the cylinder to the opposite side of the piston is connected to a source of fluid pressure such as air.

At the opposite side of the cylinder 3 to the inlet port 1 7 an outlet port 35 is provided, leading to a fluid outlet 36, there being between the outlet port from the cylinder and the fluid outlet from the body, an outlet valve 37, of essentially the same construction as the main inlet valve 1 8.

Thus at the onset of operation of the pump unit, with pressure fluid connected to the inlet 1 6 and in the absence of pressure air to the pilot valve, pressure fluid acts on the valve member 28 to increase the closing force.

Admission of pressure air to the cylinder 33 drives the piston 34 to urge the stem 30 against the valve member and open the pilot valve. The spring-loading on the valve member 24 of the main inlet valve 1 8 is such that with the pilot valve open, the fluid pressure in the passageway 1 5 is such as to open the inlet valve to flow of fluid into the cylider 3, but with the piston 4 stationary, fluid pressure is insufficient to open the outlet valve 37 against its spring loading.

With pressure fluid in the cylinder 3, the piston 4 is urged outwards into contact with the cam 14, and on rotation of the camshaft 1 3 the piston is caused to reciprocate along the cylinder to produce increased pressure on each drive stroke sufficient to open the outlet valve 37, and allow fluid to be pumped through the fluid outlet 36.

Thus, with the pump unit described above being one of a number of pump units each driven by a respective cam on the common cam shaft 13, pressure air supplied to all pilot valves results in fluid being pumped by all units, with individual units serving an individual end requirement, the units grouped and the combined outputs of each group serving a smaller number of end requirements, or the outputs from all the units combined to serve a single end requirement.

If output from a single unit or the combined output of one group, or the combined output of all the units is temporarily not required, the the supply of compressed air to the or the required selection of pilot valves can be interrupted, and when the pressure at the inlet causes the respective pilot valve to close. The immediate drop in pressure in the respective passageway 1 5 then allows the respective main inlet valve to close, preventing further supply of fluid to the respective cylinder.

Thus, despite the fact that the cam shaft continues to rotate to permit those units that are required to continue pumping so to do, continued reciprocaiton of the pistons of those selected units from which pumping is to be suspended is reduced to an idling action, until such time as pumping is again required, and effected simply by reconnecting compressed air to-the respective pilot valve.

Although not shown, each pilot valve can be connected to a relatively simple multiposition valve, for selective connection of compressed air to the pilot valves.

Claims (6)

1. A pumping system comprising a number of pump units, each of which has a piston, which of itself or by a piston rod extends to a respective drive cam, and where all the drive cams are on a common cam shaft, each pump unit having a fluid inlet, a line connecting the fluid inlet to a cylinder in which lies the piston, and a line connecting the cylinder to a valved fluid outlet, and there being in the line from- the inlet to the cylinder, a first valve to isolate the cylinder from the inlet, and a second pilot valve to isolate the first valve from the inlet, all the said pilot valves being connected to a common control means, and whereby each, pump unit or groups of pump units can be selectively activated.

2. A pumping system as in Claim 1, wherein both the first valve and pilot valve of each pump unit have a valve head spring loaded towards a valve seat, the spring loading on the valve head of each first valve being such that with the pilot valve closed, the pressure drop in the fluid in the line from the pilot valve tothe first valve, allows the first valve to close, and with the pilot valve open, the pressure of fluid in that line overcomes the spring-loading to open the first valve and connect the pump cylinder to the fluid inlet.

3. A pumping system as in Claim 1 or Claim 2, wherein the pilot valve of each pump unit incorporates a stem contacting the valve head to the opposite side to the spring, the stem extending to a piston in a cylinder unit secured to the pump unit.

4. A pumping system as in Claim 3, wherein the cylinder unit is connected to a control means in the form of a control valve to admit pressure fluid to the cylinder unit, to drive the piston along the cylinder and hence drive the stem against the pilot valve head, to open the pilot valve against its spring loading.

5. A pumping system as in Claim 4, wherein the control valve is a multi-position control valve whereby pressure fluid can selectively be delivered to activate the pilot valve of a single pump unit, a group of pump units, or all the pump units, as operating conditions may require.

6. A pumping system substantially as here inbefore described with reference to the ac companying drawing.