GB2164728A - Valve system - Google Patents

Abstract

A valve comprises a valve housing containing inlet 32 and exhaust passages (62, not shown) and first and second flow passages 36, 36' for supplying pressurised fluid to and discharging exhaust from the operating chambers of a pump. A valve member 38 is movable within the valve housing to bring the inlet and the exhaust passages alternately into communication with each of the first and second flow passages. This member has recesses 92,92', 94,94' to conduct fluid, which recesses do not extend around the complete circumference and which are preferably flat-bottomed. <IMAGE>

Description

SPECIFICATION Valve systems This invention concerns a valve system for use particularly but not solely in a double diaphragm pump. The invention also relates to individual parts of the valve system.

Conventionally, a double diaphragm pump features two diaphragm housings face to face with one another and each containing an operating chamber and a pump chamber separated by a diaphragm. The pumping chambers are connected to a common inlet through respective one-way inlet valves and to a common outlet through respective one-way outlet valves. In use, the diaphragms are displaced in unison to and fro within their housings by appropriate supply of compressed fluid to the operating chambers so that the suction stroke of one diaphragm coincides with the pumping stroke of the other and vice versa. A valve system mounted between the two housings controls the supply of compressed fluid.

One known valve system for a double diaphragm pump comprises a main inlet for pressurised fluid, a main outlet for exhaust fluid, a poppet valve for controlling communication between the main inlet and main outlet and the operating chambers of the pump, and a reciprocating piston arrangement operable by the two diaphragms to cause the poppet valve to switch the supply of compressed fluid alternately between the two operating chambers and correspondingly, the two operating chambers alternately into communication with the main outlet.

The poppet valve in this known valve system has a valve housing formed with a cylindrical chamber for the valve member. The main inlet opens into one side of this chamber and, on another side, there is a row of four openings, two of which communicate with the main outlet and the other two of which respectively communicate with the two operating chambers. The valve member, which is slidable within the cylindrical chamber, is constructed to place selected pairs of openings in communication according to its position. This is determined as follows: The valve member is a loose fit in its chamber so that compressed fluid supplied to the main inlet leaks around the member. At each end of the chamber, there is a pilot signal opening, and, at intermittent intervals, these are vented to the main outlet by the reciprocating piston arrangement.When this occurs, the pressure in one end of the valve chamber falls whilst the pressure in the other end of the chamber, generated by leakage from the pressurised fluid supply, remains substantially the same. A pressure differential is thus generated across the valve member to cause it to shoot to the low pressure end of the chamber. Here it remains, whilst pressure builds up at this end of the chamber, until the opposite end is vented to the main outlet, when it pops back to its original position. In order to allow free sliding movement of the valve member, a supply of lubricating oil is provided in the valve.

Thus, the poppet valve relies for its operation on fluid leakage, which gives rise to various problems. Firstly, the pressure differential created across the valve member for moving it may not be sufficient to overcome the retarding affect of any dirt particles which may become lodged between the valve member and its housing. Frequent maintenance may therefore be necessary. And secondly, fluid leakage tends to occur not only where desired but also between the flow of pressurised fluid to the pump operating chambers and the flow of exhaust fluid from these chambers, which reduces efficiency.

The other main element of the known valve system, the reciprocating piston arrangement, comprises a relatively simple piston housing containing passages to each of the pilot signal openings in the valve housing and a passage to the main outlet. A piston having a considerably more complex structure is received in the housing and is oil lubricated so that it is freely slidable. A network of recesses and passages in the piston allows it to connect the pilot signal passages alternately with the outlet passage as it reciprocates.

By virtue of the intricate formation of channels and grooves in the piston, it is an expensive item to produce and contributes significantly to the overall cost of the pump.

It is an object of the present invention in one form or another to overcome the problems just described.

More especially, one aim of the invention is to enable a valve system to generate a pressure signal which instead of developing gradually as a result of fluid leakage, is positively applied to a respective side of the valve member of e.g. a poppet valve for moving the member in its valve chamber.

According to a first aspect of the invention, therefore, a valve system comprises a main inlet for pressurised fluid, a main outlet for exhaust fluid, first and second flow passages for supplying pressurised fluid to and discharging exhaust fluid from first and second operating chambers, valve means operable to communicate the main inlet and the main outlet alternately with the first and the second flow passages respectively, said valve means comprising a valve member movable within a valve housing, and a reciprocating piston arrangement for operating the valve means, the reciprocating piston arrangement comprising a piston movable within a piston housing and the reciprocating piston arrangement providing, in each of two pre-determined positions of the piston, a fluid connection between the main inlet and one side of the valve member and a fluid connection between the other side of the valve member and the main outlet for creating a pressure differential thereacross for moving the valve member within the valve housing.

By connecting opposite sides of the valve member respectively to the main inlet and the main outlet through the reciprocating piston arrangement, when the piston is in each of the two pre-determined positions, a distinct pressure signal is positively directed at the valve member for moving it and the force on the valve member at this moment may be arranged to be substantially greater than is possible in the prior poppet valve described above. Operation of the valve is less likely, therefore, to be affected by the ingress of small particles into the valve housing. Further, since fluid leakage within the valve is not a requirement for its operation, the valve member can be made a snug fit in the valve housing to reduce fluid leakage generally and thereby enhance the efficiency of the valve system as a whole.

A further aspect of the invention relates to the design of the reciprocating piston arrangement rather than the valve and may, if desired, be employed in a valve system having a conventional poppet valve in which the fluid pressure for moving the valve member is established by leakage from the main inlet rather than being applied in a burst.

This second aspect of the invention features a valve assembly comprising a main inlet for pressurised fluid, a main outlet for exhaust fluid, first and second flow passages for supplying pressurised fluid to and discharging exhaust fluid from first and second operating chambers, a valve having a valve member movable within a valve housing, the valve being operable in dependence upon the position of the valve member within the valve housing to control communication between the main inlet, the main outlet and the first and the second flow passages, and a reciprocating piston arrangement for operating the valve, the reciprocating piston arrangement having a piston housing and a piston movable within the piston housing and the reciprocating piston arrangement being adapted, in each of two pre-determined positions of the piston, to cause a pressure drop on a respective side of the valve member to cause the valve member to move within the valve housing, the piston housing containing first and second pilot signal openings in communication with corresponding openings in the valve housing and an exhaust opening in communication with the main outlet, the first and second pilot openings and the exhaust opening being arranged such that a first simple recess in the piston surface communicates the first pilot signal opening with the exhaust opening in one of the two pre-determined positions and a second simple recess in the piston surface communites the second pilot signal opening with the exhaust opening in the other of the two pre-determined positions.

In this instance, the piston is of simple construction and the complex network of passages required for interconnecting the various parts of the valve system is provided in the piston housing. Such a construction offers considerable advantages over one employing a simple design of piston housing but a complex design of piston. This is because the function of the housing generally allows for greater tolerances in its construction and the manufacturing process for the housing is inherently simpler than that for the piston, so it is preferable for the housing to be the more intricate of the two.

In a preferred form of the invention, the piston housing does in fact contain an inlet opening in communication with the main inlet as well as an exhaust opening in communication with the main outlet, and the piston contains two further simple recesses arranged respectively for communicating the inlet opening with the first and the second pilot signal openings in the two pre-determined positions.

For example, the recesses arranged to cooperate with the exhaust opening may be flats in the surface of the piston, and the recesses arranged to co-operate with the inlet opening may be annular grooves in the piston surface.

In the valve system described below, no other recesses are provided.

For ease of manufacture, the piston housing advantageously comprises a housing body with a sleeve fitted into it for receiving the piston. The inlet and the outlet openings and the first and the second pilot signal openings may then be in the form of recesses in the surface of the housing body facing the sleeve,and the sleeve may include first and second pilot signal ports opening into the first and the second pilot signal openings, first and second inlet ports opening into the inlet opening and at least one exhaust port opening into the exhaust opening.

The particular design envisaged in this application includes a sleeve formed with two rows of these ports extending in its longitudinal direction. One row includes the first and second inlet ports, and the other row includes the first and the second pilot signal ports and the or each exhaust port. The other row may, in addition, include a first auxiliary port opening into the first pilot signal opening in the housing body and facing the first inlet port, and a second auxiliary port opening into the second pilot signal opening in the housing body and facing the second inlet port.

Further aspects of the invention reside in the poppet valve and the reciprocating piston arrangement themselves. Both of these are designed for oil free operation with one or more of the sliding surfaces in each being provided by a self lubricating material.

The invention is described further by way of example, with reference to the accompanying drawings: FIGURE 1 is a diagrammatic view of a double diaphragm pump incorporating a valve system according to the present invention, showing the valve system in a first stage of its operating cycle; FIGURE 2 is a diagrammatic view of the valve system in a second stage of its operating cycle; FIGURE 3 is a diagrammatic view of the valve system in a third stage of its operating cycle; FIGURE 4 is a diagrammatic view of the valve system in a fourth stage of its operation; FIGURE 5 is a section through a poppet valve of the valve system shown in Figures 1 to 4; FIGURE 6 is a section along the line 6-6 in Figure 5; FIGURE 7 is a section along the line 7-7 in Figure 5;; FIGURE 8 is a longitudinal section through a reciprocating piston arrangement of the valve system illustrated in Figures 1 to 4, showing a piston of the reciprocating piston arrangement in a first position; FIGURE 9 is a longitudinal section through the reciprocating piston arrangement along the line 9-9 in Figure 8, showing the piston in outline in the same position as in Figure 8; FIGURE 10 is a longitudinal section through the reciprocating piston arrangement along the line 10-10 in Figure 8, showing the piston in outline in the same position as in Figure 8; FIGURE 11 is a view similar to Figure 8 but showing the piston in a second position; FIGURE 12 is a view similar to Figure 8 but showing the piston in a third position; FIGURE 13 is a section through-a modified poppet valve for use in the valve system illustrated in Figures 1 to 4;; FIGURE 14 is a section along the line 14-14 in Figure 13; FIGURE 15 is a section along the line 15-15 in Figure 13; FIGURE 16 is a perspective view of the valve member of the valve illustrated in Figure 13; and FIGURE 17 to 19 illustrate further applications of the valve system illustrated in Figures 1 to 16; Referring firstly to Figure 1, a double diaphragm pump includes first and second diaphragm housings 10,10' each separated into a pumping chamber 12,12ft and an operating chamber 14,14' by a diaphragm 18,18'. The pumping chambers 12,12' are connected by way of respective one-way inlet valves 18,18' to a common pump inlet 20 and by way of respective one-way outlet valves 22,22ft to a common pump outlet 24.As described below, the diaphragms 18,18ft are movable in unison to and fro within their housings 10,10' so that the volume of one pumping chamber increases while that of the other decreases. Consequently, the suction stroke of one diaphragm coincides with the pumping stroke of the other.

During the suction stroke of a respective diaphragm 18, the associated inlet valve 18 is drawn open to admit fluid from the pump inlet 20 to the pumping chamber 12 while the associated oultet valve 22 is held closed to prevent such fluid from passing to the pump outlet 24. In the pumping stroke, the diaphragm 18 forces the fluid out through the outlet valve 22 to the pump outlet 24 and the pressure in the pumping chamber 12 holds the inlet valve 18 closed.

In the condition illustrated in Figure 1, the diaphragm 16 is about to commence its pumping stroke and the diaphragm 16' is about to commence its suction stroke.

Operation of the diaphragmsl6,16' is controlled by a valve system shown diagrammatically in Figures 1 to 4 and generally designated 26. This valve system is normally integrated into a unit mounted between the two diaphragm housings 10,10'. It has two main elements, namely a poppet valve generally designated 28 and a reciprocating piston arrangement generally designated 30.

The poppet valve 28 is operable to control the supply of pressurised fluid from a main inlet 32 for pressurised fluid to each of the pump operating chambers 14,14' and to control venting of each of the pump operating chambers 14,14' to a main outlet (not shown) for exhaust fluid. And the reciprocating piston arrangement 30 operates the poppet valve 28.

For this purpose, the valve 28 comprises a valve housing 34 into which the main inlet 32 opens and which contains fluid flow passages 36,36' in communication with the pump operating chambers 14,14', and exhaust passages (not shown) connected to the main outlet; A generally cylindrical valve member 38 is movable within a generally cylindrical valve chamber 40 in the housing 34 to connect the main inlet 32 and the main outlet alternately with each of the flow passages 36,36'. The valve housing 34 also contains two pilot signal openings 42,42' at opposite ends of the chamber 40, and these serve to transmit a pressure signal into the chamber 40 for moving the valve member 38 to switch over the connections between the main inlet 32, the main outlet and the two operating chambers 14,14';.

The reciprocating piston arrangement 30 comprises a piston housing 44 within which a piston 46 is slidable. The piston 46 is secured at its opposite ends to the two diaphragms 16,16' so that it is movable to and fro by the diaphragms within its housing. The piston housing 44 contains an inlet opening 48 connected directly to the main inlet 32 and an exhaust opening 50 communicating with the main outlet. Additionally, the piston housing 44 contains two pilot signal openings 52,52' which are connected to the pilot signal openings 42,42' respectively in the valve housing 34.

The construction of the valve 28 and the reciprocating arrangement 30 will be described in greater detail below. First, the operating cycle of the valve system 26 will be explained with reference to Figures 1 to 4.

This cycle is repetitive but it is convenient to consider the condition illustrated in Figure 1 as the first stage. At this moment, the piston 46 is at one extreme end of its travel and, in this position, it provides fluid connections firstly between the inlet opening 48 and the pilot signal opening 52' in the piston housing 44 and secondly between the pilot signal opening 52 and the exhaust opening 50 in the piston housing 44. Consequently, the main inlet 32 for pressurised fluid is connected to the pilot signal opening 42' in the valve housing 34 and the pilot signal opening 42 in the valve housing 34 is connected to the main outlet. A pressure differential is thereby created across the valve member 38 to move it to the position indicated. The valve member 38 then connects the main inlet 32 to the pump operating chamber 14, and the pump operating chamber 14' to the main outlet.

Turning to Figure 2, it can be seen that the valve 28 now remains in the state in which it was set in the stage of the operating cycle represented in Figure 1. Thus, pressurised fluid is being supplied to the operating chamber 14 so that the diaphragm 16 pumps fluid from the pumping chamber 12; and the operating chamber 14' is being exhausted to cause the diaphragm 16' to draw fluid into the pumping chamber 12'. On the other hand, the piston 46 has been dispiaced by the diaphragmsl6,16' away from the extreme end position illustrated in Figure 1 and closes the inlet and exhaust openings 48,50 and the pilot signal openings 52,52' in the piston housing 44.

In the next stage of the operating cycle, shown in Figure 3, the piston 46 has reached the other extreme end of its movement. The piston again connects the inlet and the outlet openings 48,50 to the pilot signal openings 52,52' but in reverse. As a result, the inlet opening 48 is connected to the pilot signal opening 52 and the pilot signal opening 52' is connected to the exhaust opening 50. The main inlet 32 is therefore connected to the pilot signal opening 42 in the valve housing 34 whereas the pilot signal opening 42' is in communication with the main outlet. A burst of pressure from the main inlet 32 is thus introduced into the associated end of the valve housing 34 while its other end is vented to the exhaust, and this pressure signal, positively applied to the valve member 38, moves it to the opposite end of its chamber.This places the pump operating chamber 14 in communication with the main outlet, and the main inlet 32 in communication with the pump operating chamber 14'.

The movement of the diaphragms 16,16' is thus reversed, as illustrated in Figure 4, with the diaphragm 16 performing a suction stroke and the diaphragm 16' performing a pumping stroke. Figure 4 shows again how the piston 46 closes the inlet and exhaust openings 48,50 from the pilot signal openings 52,52' once it has moved from the extreme end position.

Next, the piston 46 returns to the position illustrated in Figure 1 and the cycle is repeated.

The construction of the poppet valve 28 is shown in greater detail in Figures 5 to 7.

As indicated, the main inlet 32 is located at the top of the valve housing 34 and supplies pressurised fluid into a tube 54 which projects into the valve chamber 40. The valve member 38 contains a slot 56 receiving the tube 54 and opening into two supply passages 58,58' located within the body of the valve member 38. These supply passages 58,58' are spaced axially in the central region of the valve member 38 and are angled slightly towards the front of the valve housing 34 (see Figure 6).

This enables the supply passages 58,58' to communicate with the fluid flow passages 36,36', which are disposed towards the front of the housing 34 and are also spaced apart in the axial direction. The arrangement of the passages 58,58' and the passages 36,36' is such that a respective pair of these passages is aligned in each end position of the valve member 38.

Behind the fluid flow passages 36,36' are the exhaust passages 62,62'. At the ends of the valve member 38 there are two annular grooves 60,60' for bringing the fluid flow passages 36,36' into communication with the exhaust passages 62,62'. The arrangement of these annular grooves 60,60' is such that, when one of the supply passages 58' is aligned with the associated fluid flow passage 36', the annular groove 60 remote from that supply passage 58' is aligned with the other fluid flow passage 36. Hence, when the main inlet 32 is connected through the valve member 38 to the fluid flow passage 36' as illustrated in Figure 6, the fluid flow passage 36 is connected to the exhaust passage 62 as illustrated in Figure 7. It should be noted from Figure 6, that the valve member 38 closes the exhaust passage 62' which is situated behind the fluid flow passage 36'.

In Figure 5, the pilot openings 42,42' can be seen at opposite ends of the bottom of the valve housing 34. A narrow region 64,64' of enlarged diameter is provided between each pilot signal opening 42,42' and the extreme end of the valve chamber 40. The valve member 38 is formed with a raised central portion 66 66' at each end, and this raised central portion and the enlarged region of the valve chamber 40 together define an annular space when the valve member 38 is at the associated end of the chamber 40 into which pressurised fluid can flow through the adjacent pilot signal opening 42,42'. This allows the pilot signal to be positively applied to the relevant end of the valve member 38.

In this instance, the valve member 38 is formed from carbon filled PTFE, which is an impact resistant, self-lubricating, material. Consequently, no lubricating oil is required in the valve 28 to assist movement of the valve member 38. The member 38 is a snug sliding fit within the housing 34 and is maintained in the appropriate orientation by the engagement of the tube 54 in the slot 56. Should the valve member 38 jam within the housing 34 for any reason, it can be released by a punch 68 situated in one end wall of the housing 34.

A connection line 70 extending from the main inlet 32 towards the bottom of the valve housing 34 is shown in dotted lines in Figure 6. This connection line 70 leads to the piston housing 44 and is in communication with the inlet opening 48 therein.

Details of the reciprocating piston arrangement are shown in Figures 8 to 12.

The piston housing 44 comprises a housing body 72 and a sleeve 74 fitted into the body for receiving the piston 46. The sleeve is formed from bronze filled PTFE which is a self-lubricating load bearing material so that no lubricating oil is required within the piston arrangement 30.

The interior surface of the body 72 is formed with a complex array of recesses separated by dividing walls.

These recesses and walls can best be seen in Figures 8 to 10 and include an axial recess on one side of the body 72 (see Figure 10) extending almost the full length of the housing 44 and providing the inlet opening 48 into which the connection line 70 from the valve housing 40 opens. A continuous wall 76 surrounds the opening 48 to separate it from other recesses in the body 72.

On the opposite side of the body 72, a labyrinthine wall 78 defines a central square recess providing the exhaust opening 50 in the piston housing 44, and two F shaped recesses providing the pilot signal openings 52,52'. These F shaped recesses are inverted relative to one another and intermeshed about the exhaust opening 50 as illustrated in Figure 9.

The sleeve 74 contains two rows of ports opening into the various recesses. More especially, one row contains only two inlet ports 80 situated at opposite ends of the enlongate recess providing the inlet opening 48. The other row contains six ports. The central two, 82, of these six ports open into the exhaust opening 50. On each side of the exhaust ports 82, there is a respective pilot signal port 84,84' opening into an associated one of the pilot signal openings 52,52'. Finally, at each end of this second row, there is a respective auxiliary pilot signal port 86,86' also opening into the associated pilot signal opening 52,52'.

The piston 46 itself is of relatively simple construction having a respective annular groove 88,88' adjacent each end and a respective flat 90,90' spaced a little way in from each end on the side of the piston facing the row of six ports in the sleeve 74.

In Figures 8 to 10, the piston is illustrated in the extreme end position corresponding to the stage in the operating cycle of the valve system represented in Figure 1. In this position, the annular groove 88 allows communication between one inlet port 80 in the sleeve 74 and the auxiliary pilot signal port 86'. The main inlet 32 is thus connected by way of the connection line 70 in the valve housing 40 to the pilot signal opening 52' in the housing body 72, and thence to the pilot signal opening 42' in the valve housing 40. Simultaneously, the flat 90 in the piston surface connects the pilot signal port 84 in the sleeve 74 to one of the exhaust ports 82. The pilot signal opening 52 in the housing body 72, and thence the pilot signal opening 42 in the valve housing 40, is thus connected to the exhaust opening 50.

Figure 11 shows how the piston 46 closes the ports 80 to 86 when it is in an intermediate position. It follows that the main inlet 32 and the main outlet are blocked from the pilot signal openings 52,52' in the piston housing 44 and from the pilot signal openings 42,42' in the valve housing 40 at this time.

The piston 46 is at the opposite extreme end of its travel in Figure 12 and here connects the other inlet port 80 to the auxiliary pilot port 86 by way of the annular groove 88, and the pilot port 84' to the other exhaust port 82 by way of the flat 90'.

A modified form of poppet valve is shown in Figures 13 to 16. For ease of understanding, like parts are designated by the same reference numerals as in Figures 1 to 12.

The main differences between this valve and the previous one lie in the disposition of the main inlet 32 and in the design of the valve member 38. The fluid flow passages 36,36', the exhaust passages 62,62' and the pilot signal openings 42,42' are arranged as described above.

In this instance, the main inlet 32 branches into two inlet passages 32a and 32b which open into the valve chamber 40 generally opposite the fluid flow passages 36,36' respectively. The valve member 38 is formed with a pair of simple slots 92,92' in its surface for connecting the supply passages 32a, 32b with the fluid flow passages 36,36'. A further pair of simple slots 94,94' is provided in the surface of the valve member 38 for connecting the fluid flow passages 36,36' with the exhaust passages 62,62'. The slots 92,94 are angled relative to one another as shown in Figure 16 with the slots 92 being situated between the slots 94.

Narrow bores 96,96' are also formed through the valve member 38 at its ends to provide a bleed path from the inlet 32 to the previously pressurised end of the valve chamber 40 in each position of the valve member 38. This bleed path functions to maintain the pressure level in that end of the chamber 40 and thus to hold the valve member 38 in its existing position until the pilot signal is applied to switch the valve 28 over to the new position. The bores 96,96' must be narrower than the pilot signal openings 42,42' in order to avoid generating pressure in apposition to the pilot signal.

As a minor variation on the construction illustrated in Figures 5 to 7, the present valve features a central recess 98,98' in each end of the valve member 38 and a channel 100, 100' extending from the recess to the bottom of the chamber 40 for ensuring that pressure in the pilot signal openings 42,42' can reach and act on the end surfaces of the valve member when the member abuts the ends of the valve chamber 40.

A pin 102 mounted at one end of the valve chamber 40 is arranged to project into a blind bore 104 in the valve member 38 for locating the member in the correct orientation within the chamber.

As before, the valve member 38 is manufactured from a self-lubricating material such as carbon filled PTFE.

Finally, Figures 17 to 19 exhibit other applications of the valve system previously described. In each case, the valve system is contained within a unit generally designated 106 and it operates in the manner already specified.

Referring initially to Figure 17, this shows portions of a gas intensifier generally designated 108 having booster housings 110,110'.

The booster housings contain piston drive assemblies 112,112' movable within the housings by appropriate supply of compressed fluid through the unit 106 and the passages 36,36'. The piston 46 is mounted between the piston drive assemblies 112,112' as indicated.

A first staging chamber 114' is provided in the housing 110' and a second, smaller, staging chamber 114 is provided in the housing 110. Reciprocation of the piston drive assemblies 112,112' causes gas to be drawn into the chamber 114' and compressed therein and subsequently supplied by passages (not shown) to the chamber 114 for further compression.

Figure 18 relates to a generally similar type of construction intended for the high pressure pumping of caustic materials. This construction includes slightly modified piston drive assemblies 112,112' and pumping chambers 114,114' of similar rather than differing dimensions. In other respects, the operation is substantially the same as described with reference to Figure 17.

In Figure 19, the valve system is employed in a conveyor system. The unit 106 controls the supply of pressurised fluid into two extension pipes 116,116' leading to cylinders 118,118'. The piston 46 extends between these cylinders and has mounted thereon a pair of hinged fingers 120,120'. These fingers depend downwardly from the piston 46 towards a conveying surface 122 on which packages 124 stand. As the piston 46 reciprocates by appropriate application of pressure to the cylinders 118,118' under the control of the unit 106, the fingers 120,120' advance the packages in the following manner.

When the piston moves to the left, the fingers are carried with it and are lifted on their hinges by the packages 124. The fingers drop behind the packages and when the piston 46 moves to the right they engage the rear ends of the packages and move them forwards.

The present invention thus offers a valve system having various applications, which operates efficiently and economically and which is relatively simple to manufacture.

The invention resides not only in the valve system as a whole but also in the individual parts of it in their own right.

Claims (19)

1. A valve system comprising a main inlet for pressurised fluid, a main outlet for exhaust fluid, first and second flow passages for supplying pressurised fluid to and discharging exhaust fluid from first and second operating chambers, valve means operable to communicate the main inlet and the main outlet alternately with the first and the second flow passages respectively, said valve means comprising a valve member movable within a valve housing, and a reciprocating piston arrangement for operating the valve means, the reciprocating piston arrangement comprising a piston movable within a piston housing and the reciprocating piston arrangement providing, in each of two pre-determined positions of the piston, a fluid connection between the main inlet and one side of the valve member and a fluid connection between the other side of the valve member and the main outlet for creating a pressure differential thereacross for moving the valve member within the valve housing.

2. A system as claimed in claim 1, in which the piston housing contains first and second pilot signal openings in communication with corresponding openings in the valve housing, an inlet opening in communication with the main inlet, and an exhaust opening in com munication with the main outlet, the piston being adapted to communicate the inlet and the outlet openings with the first and second pilot signal openings respectively, in one of the two pre-determined positions, and with the second and the first pilot signal openings respectively, in the other of the two pre-determined positions.

3. A system as claimed in claim 2, in which the piston housing comprises a housing body, and a sleeve fitted into the housing body for receiving the piston, and in which the inlet and the outlet openings and the first and the second pilot signal openings are in the form of recesses in the surface of the housing body facing the sleeve, the sleeve including first and second pilot signal ports opening into the first and the second pilot signal openings in the housing body respectively, first and second inlet ports opening into the inlet opening in the housing body, and at least one exhaust port opening into the exhaust opening in the housing body.

4. A system as claimed in claim 3, in which the sleeve is formed with two rows of the ports extending in its longitudinal direction, one row including the first and the second inlet ports and the other row including the first and the second pilot signal ports and the at least one exhaust port.

5. A system as claimed in claim 4, in which the other row further includes a first auxiliary port opening into the first pilot signal opening in the housing body and facing the first inlet port, and a second auxiliary port opening into the second pilot signal opening in the housing body and facing the second inlet port.

6. A system as claimed in any of claims 2 to 5, in which the surface of the piston is formed with recesses arranged to communicate the associated openings in each of the two pre-determined positions.

7. A system as claimed in claim 6, in which the recesses include a first annular groove for communicating the main inlet with one side of the valve member in one of the two pre-determined positions and a second annular groove for communicating the main inlet with the other side of the valve member in the other of the two pre-determined positions.

8. A system as claimed in claim 6 or 7, in which the recesses include a first flat for communicating one side of the valve member with the main outlet in one of the two pre-determined positions and a second flat for communicating the other side of the valve member with the main outlet in the other of the two pre-determined positions.

9. A system as claimed in any preceding claim, in which the valve housing contains a generally cylindrical valve chamber formed with first and second pilot signal ports at opposite ends thereof for transmitting the pressures from the main inlet and the main outlet to the opposite sides of the valve member.

10. A system as claimed in any preceding claim, in which the valve member and the valve housing are formed from materials permitting oil free sliding of the valve member within the valve housing.

11. A system as claimed in any of claims 2 to 8, in which the piston housing and the piston are formed from materials permitting oil free sliding of the piston within the piston housing.

12. A valve system comprising a main inlet for pressurised fluid, a main outlet for exhaust fluid, first and second flow passages for supplying pressurised fluid to and discharging exhaust fluid from first and second operating chambers, a valve having a valve member movable within a valve housing, the valve being operable in dependence upon the position of the valve member within the valve housing to control communication between the main inlet, the main outlet and the first and the second flow passages, and a reciprocating piston arrangement for operating the valve, the reciprocating piston arrangement having a piston housing and a piston movable within the piston housing and the reciprocating piston arrangement being adapted, in each of two pre-determined positions of the piston, to cause a pressure drop on a respective side of the valve member to cause the valve member to move within the valve housing, the piston housing containing first and second pilot signal openings in communication with corresponding openings in the valve housing and an exhaust opening in communication with the main outlet, the first and second pilot openings and the exhaust opening being arranged such that a first simple recess in the piston surface communicates the first pilot signal opening with the exhaust opening in one of the two pre-determined positions and a second simple recess in the piston surface communicates the second pilot signal opening with the exhaust opening in the other of the two pre-determined positions.

13. A double diaphragm pump including a valve system as claimed in any preceding claim.

14. A poppet valve for use in a valve system as claimed in any of claims 1 to 12 or in a double diaphragm pump as claimed in claim 13, in which a portion at least of the valve member and/or a portion at least of the valve housing is formed from a material permitting oil free operation of the valve.

15. A reciprocating piston arrangement for use in a valve system as claimed in any of claims 1 to 12 or in a double diaphragm pump as claimed in claim 13, in which at least a portion of the arrangement is formed from a material permitting oil free reciprocation of the piston.

16. A poppet valve substantially as herein particularly described with reference to and as illustrated in the accompanying drawings.

17. A reciprocating piston arrangement substantially as herein particularly described with reference to and as illustrated in the accompanying drawings.

18. A valve system substantially as herein particularly described with reference to and as illustrated in the accompanying drawings.

19. A double diaphragm pump substantially as herein particularly described with reference to and as illustrated in the accompanying drawings.