GB2476075A

GB2476075A - Solenoid operated valve

Info

Publication number: GB2476075A
Application number: GB0921629A
Authority: GB
Inventors: Dennis Majoe
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-12-10
Filing date: 2009-12-10
Publication date: 2011-06-15
Also published as: GB0921629D0; WO2011070558A2; WO2011070558A3

Abstract

A valve 30 comprises a chamber 32 having a first port 34, a valve seat 44 disposed within or formed by a wall of the chamber, and a tubular valve member 40 movable by a solenoid 38 and spring 46. A first end 42 of the valve member is movable relative to the valve seat between a closed position in which the first end of the valve member engages the valve seat, and an open position in which the first end of the valve member is spaced from the valve seat. The valve member leads from its first end to a second port 36 of the valve outside the chamber. The operating force required to open the valve is reduced compared to a similar valve with a solid valve member. The valve member acts as the armature of the solenoid.

Description

TITLE

Valves

DESCRIPTION

This invention relates to valves.

The invention was conceived in connection with a solenoid-operated pneumatic control valve for a robotic actuator. However, the invention is also applicable to valves for other gases and liquids, for other uses and operated by other means.

Figures 1A and lB of the accompanying drawings schematically show a simple solenoid-operated pneumatic valve 10 of the direct-acting type for use with a robotic actuator. A chamber 12 has an inlet port 14 and an outlet port 16. The chamber 12 contains a solenoid 18 having an armature 20 which is formed at one end with a valve head 22. The armature 20 and valve head 22 are movable between (a) a closed position shown in Figure 1A in which the valve head 22 engages an annular seal 24 around the outlet port 16 so that air cannot pass from the chamber 12 into the outlet port 16 and (b) an open position shown in Figure lB in which the valve head 22 is spaced from the seal 24 so that air can pass from the chamber 12 into the outlet port 16 and can therefore flow from the inlet port 14 to the outlet port 16. A light spring 26 urges the valve head 22 towards the closed position, and the solenoid 18 can be activated to pull the valve head 22 to the open position.

In the simple example shown, the force FSTART that the solenoid 18 needs to exert on the armature 20 in order to start opening the valve 10 is approximately given by: FSTART = SMIN + lt.(PIN.D12 -POuTD22)/4 where: SMIN is the force of the spring when the valve is closed; PIN is the pressure at the inlet port 14; POUT is the pressure at the outlet port 16; Di is the outer diameter of the annular seal 24; and D2 is the inner diameter of the annular seal 24. To a rough approximation, this simplifies to FSTART = (PIN -POUT).A, where A is the solid cross-sectional area of the valve head.

Typically, the inlet port pressure PIN may be the pump pressure of the pneumatic system, and the outlet port pressure POUT may be atmospheric pressure, and so the operating force that the solenoid 18 needs to exert on the armature 20 in order to start opening the valve can be substantial. It should be noted, however, that, once the valve is open, the solenoid 18 needs to exert only a small force on the armature 20 sufficient to keep the light spring compressed in order for the valve to stay open.

The valve 10 of Figures 1A and lB cannot operate properly if the pressure at the port 16 is higher than the pressure at the port 14 (i.e. the inlet port becomes the outlet port, and vice versa) unless the solenoid 18 is oppositely acting, or double-acting, and can therefore apply a pushing force to the armature 20.

In order to reduce the operating force required of the solenoid, more complex indirect-acting or servo-assisted valves have been developed. In an example of such a valve, a small direct-acting pilot valve controls air flow through a small passageway between a chamber on one side of a diaphragm and an outlet port. The opposite side of the diaphragm can block and open a large passageway between an inlet port and the outlet port to close and open the valve as a whole. The diaphragm is perforated by a small hole between the inlet port and the chamber.

Although an indirect valve of this type requires only a small force to operate the pilot valve, there is a delay, upon opening of the pilot valve, while air flows through the small passageway and the pilot valve to enable the diaphragm to move to open the valve as a whole. Furthermore, there is a delay, upon closing of the pilot valve, while air flows through the small hole in the diaphragm to enable the diaphragm to move to close the valve as a whole. Moreover, there can be a problem with blockage of the small hole, small passageway and pilot valve by debris. It should also be noted that this type of indirect-acting valve will open if the outlet pressure becomes higher than the inlet pressure. Furthermore, the force required of the solenoid to open the pilot valve needs to be maintained to keep the valve as a whole open.

An aim of the present invention, or at least of specific embodiments of it, is to provide a valve which is simple in construction, which is relatively small, which for its relatively small size can handle high pressures and flow rates, which for its high pressure and flow rate capability requires a relatively small actuating force and has a relatively fast response time, which can operate with a single-acting actuating force despite reversal of the pressure difference across the valve, and which is relatively immune to clogging.

In accordance with the present invention, there is provided a valve comprising: a chamber having a first port; a valve seat disposed within or formed by a wall of the chamber; and a tubular valve member movable relative to the chamber along the longitudinal axis of the tubular valve member. As a result of such movement, a first end of the valve member is movable relative to the valve seat between: a closed position in which the first end of the tubular valve member engages the valve seat so that the valve seat closes the first end of the tubular valve member, and an open position in which the first end of the valve member is spaced from the valve seat. The tubular valve member leads from its first end to a second port of the valve outside the chamber.

The valve of the invention is therefore based on the direct-acting valve described with reference to Figures 1A & B and does not suffer the disadvantages of the indirect-acting valve.

Furthermore, by providing a tubular valve member, the operating force required to open the valve can be substantially reduced. As discussed above, in the prior art of Figures 1A & B, the force FSTART pressing the valve member against the valve seat is approximately proportional to the product of the pressure difference across the valve member and the solid cross-sectional area of the valve member. By contrast, in some embodiments of the invention, the pressures are not applied to the tubular valve member in its direction of movement when the valve is closed and therefore have no effect. In other embodiments, one of the pressures is applied to the valve member in its direction of movement, but acting only on the annular cross-section of the tubular member. By providing the tubular member with a thin wall thickness, this area can be reduced to a small fraction of the solid cross-sectional area of the valve member of the prior art.

The valve preferably includes an actuating means operable to move the tubular valve member so that the first end thereof moves between the closed and open positions. The actuating means preferably includes a solenoid which can be actuated to move the tubular valve member so that the first end thereof moves from one of the closed and open positions to the other of those positions. A resilient element may be arranged to urge the tubular valve member in the opposite direction to the solenoid. The solenoid may be mounted inside the chamber.

The tubular valve member preferably acts as an armature of the solenoid and passes through a stator of the solenoid.

The valve preferably further includes sealing means for sealing the tubular valve member to a wall of the chamber such that the valve member can move relative to the chamber.

In various embodiments of the invention, the sealing means comprises an 0-ring or the like sliding seal, a flexible diaphragm and a variable length hose.

A specific embodiment of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figures 1A & B are schematic views of a direct-acting valve following the teachings of the prior art, in closed and open states, respectively; Figures 2A & B are schematic views of a direct-acting valve of a first embodiment of the invention, in closed and open states, respectively; Figures 3A & B are schematic views of a direct-acting valve of a second embodiment of the invention, in closed and open states, respectively; Figure 3C is an isometric view showing the shape of a diaphragm used in the valve of the second embodiment, when the valve is closed; Figures 4A & B are schematic views of a direct-acting valve of a third embodiment of the invention, in closed and open states, respectively; Figures 5A & B are schematic views of a direct-acting valve of a fourth embodiment of the invention, in closed and open states, respectively; and Figure 5C is a section view of the valve of Figure 5B taken on the section line 5C-5C.

Referring to Figures 2A & B, the first embodiment of valve 30 for use with a robotic actuator has a chamber 32 with a first port 34 and a second port 36. The chamber 32 contains a solenoid 38 having a tubular armature 40 passing through a stator of the solenoid 38. One end 42 of the armature 40, to the right of the solenoid 38, is aligned with and can make sealing contact with a seal 44 fixed to a wall of the chamber 32. The seal may be provided by a disc of silicone. A light compression coil spring 46 acts to urge the end 42 of the armature 40 to the right against the seal 44 as shown in Figure 2A so that the valve 30 is closed, but the solenoid 38 can be actuated by an electric current supplied through wires (not shown) to overcome the force of the spring 46 and pull the end 42 of the armature 40 to the left away from the seal 44 so that the valve 30 becomes open, as shown in Figure 2B. The other end 48 of the tubular armature 40, to the left of the solenoid 38, is slidable through an 0-ring 50 mounted in a hole in the wall of the chamber 32 leading to the second port 36.

The tubular armature 40 has outer and inner diameters Di and Dz, respectively. The absolute pressures at the first and second ports 34,36 when the valve 30 is closed are Pi and P2, respectively. The spring force of the spring 46 when the valve 30 is closed is SMIN. Assuming that the tubular armature 40 makes contact with the seal 44 across its whole wall thickness, then the force FCLOSED urging the end 42 of the armature 40 against the seal 44 when the valve is closed and the solenoid 38 is not actuated is given by FCLOSED = lt.P2.(Di2 -D22)/4 + SMIN. The force FCLOSED is independent of the pressure difference Pi -P2 across the closed valve 40 and will always be positive. The valve 40 will therefore remain closed regardless of whether Pi is greater than or less than P2.

Ignoring friction between the armature 40 and the 0-ring 50, the force FCLOSED is equal and opposite to the force FSTART which the solenoid 38, when actuated, needs to apply to the armature 40 in the opposite direction in order to start opening the valve 30. For a thin-walled tubular armature 40, as Di -D2 tends towards zero, the force FCLOSED tends towards SMIN, and the force FSTART tends towards -SMIN. The spring 46 is light, and therefore both forces FCLOSED and FSTART are relatively small.

As the valve 30 opens to its fully open state, the force in the spring 46 increases to SMAX. The pressure PFLOW throughout the valve 30 will be approximately constant and not exert any net force on the armature 40. The solenoid 38 therefore needs to be able to maintain a force FHOLD on the armature equal and opposite to the maximum spring force SMAX in order to hold the valve 30 open.

When the solenoid 38 is deactivated, provided the maximum spring force SMAX is sufficient to overcome the stiction between the 0-ring 50 and the armature 40, the valve 30 will begin to close, and provided the spring force which decreases to SMIN is sufficient to exceed the friction between the 0-ring 50 and the armature 40, the valve 30 will return to its fully closed state.

Figures 3A & B show a second embodiment of valve 30 which is similar to the first embodiment of Figures 2A & B except in the following respects and which is arranged to eliminate friction between the tubular armature 40 and the wall of the chamber 32.

In the valve 30 of Figures 3A to C, the 0-ring 50 is omitted, and instead an annular diaphragm 52 seals the end 48 of the tubular armature 40 to the wall of the chamber 32. The diaphragm 52 is very thin and very flexible, but substantially inextensible. The wall section of the diaphragm 52 when relaxed is quarter circular. The diaphragm 52 lies, at its outer edge, tangentially to a common plane both when the valve 30 is filly closed (Figure 3A) and when it is fully open (Figure 3B) and is secured to the wall of the chamber 32 at a diameter D3. At its inner edge, the diaphragm 52 lies tangentially to the outer cylindrical surface (diameter Di) of the tubular armature 40 both when the valve 30 is fully closed (Figure 3A) and when it is fully open (Figure 3B). It will therefore be appreciated that, when the valve 30 is fully closed, the diaphragm 52 applies a force FDIA to the right on the tubular armature given by FDIA = -it.(Pi -P2).(D32 -Di2)/4. At the other end 42 of the tubular armature 40, it is belled out from its outer and inner diameters Di, D2 to enlarged outer and inner diameters D4, D5 for contacting the valve seat 44. When the valve is closed, the pressure Pi at the first port 34 is greater than the pressure P2 at the second port 36 and the solenoid 38 is deactivated, the forces that combine to form the force FCLOSED pressing the belled end 42 of the armature 40 against the seat 44 are: -it.(Pi -P2).(D32 -Di2)/4 applied by the diaphragm 52; lt.P2.(Di2 -D22)/4 applied on the left end 48 of tubular armature 40; -lt.P2.(D52 -D22)/4 applied on the inside of the belled end 42 of the armature 40; lt.Pi.(D42 -Di2)/4 applied on the outside of the belled end 42 of the armature 40; and SMIN applied by the spring 46.

Summing these forces gives FCLOSED = SMIN + lt.{Pi.(D42 -D32) + P2.(D32 -D52)}/4.

The diameter D3 at which the diaphragm 52 is attached to the wall of the chamber 32 may be chosen to be equal to the outer diameter D4 of the belled end 42 of the armature, so that the equation simplifies to FCLOSED = SMIN + lt.P2.(D42 -D52)/4. Similarly to the first embodiment of Figures 2A & B, the term lt.P2.(D42 -D52)/4 tends to zero as the wall thickness D4 -D5 of the belled end 42 of the armature 40 tends to zero. Also, the force FCLOSED is independent of the pressure difference Pi at the first port 34. However, if the pressure Pi is less than the pressure P2 when the valve 30 is closed, the diaphragm 52 will flip compared to the shape shown in Figure 3A so that, at its inner edge, the diaphragm 52 lies tangentially to the plane of the left end 48 of the armature 40. The diaphragm 52 will therefore not contribute to the force FCLOSED, which then becomes FCLOSED = SMIN + lt.{Pi.(D42 -D22) + P2.(D42 -D52)}/4. This force will always be positive, and the valve 30 will therefore remain closed regardless of whether Pi is greater than or less than P2.

Figures 4A & B show a third embodiment of valve 30 which is similar to the first embodiment of Figures 2A & B except in the following respects and which, again, is arranged to eliminate friction between the tubular armature 40 and the wall of the chamber 32.

In the valve 30 of Figures 4A & B, the chamber 32 has a long extension portion 52 between the solenoid 38 and second port 36. A flexible hose 54 of silicone having the same outer and inner diameters Di,D2 as the tubular armature 40 is a loose fit in the chamber portion 52 and is bonded the left end 48 of the armature 40 and to the chamber portion wall immediately next to the second port 36. The hose 54 may be sufficiently flexible that it applies negligible force to the armature 40 when the hose 54 contracts and extends in length as the valve 30 opens and closes. Alternatively, the hose 54 may be chosen so that it performs the same function as the spring 46, and the spring 46 may be omitted. In order to prevent the hose 54 collapsing on itself when the valve 30 is closed and the pressure Pi is substantially greater than the pressure P2, the hose 54 is lined with a coil 56 of fine steel wire having a small coil pitch. Additionally, or alternatively, in order to prevent the hose 54 barrelling out when the valve 30 is closed and the pressure P2 is substantially greater than the pressure Pi, the hose 54 may be wrapped with a coil (not shown) of fine steel wire having a small coil pitch.

The fourth embodiment of Figures 5A to C is similar to the first embodiment of Figures 2A & B except that: the valve seat 44 is provided inside the chamber 32 on a dividing wall 58 which is perforated around the valve seat 44; the first and second ports 14,16 are aligned; and the solenoid 38 is disposed to the opposite side of the 0-ring 50 so that the solenoid 38 is always exposed to the pressure at the second port 16, rather than always being exposed to the pressure at the first port 14.

It should be noted that the embodiments of the invention has been described above purely by way of example and that many modifications and developments may be made thereto within the scope of the present invention.

Claims

CLAIMS(The reference numerals in the claims are not intended to limit the scope of the claims.) 1. A valve (30) comprising: a chamber (32) having a first port (34); a valve seat (44) disposed within or formed by a wall of the chamber; and a tubular valve member (40) movable relative to the chamber along the longitudinal axis of the tubular valve member so that a first end of the valve member is movable relative to the valve seat between: a closed position in which the first end of the tubular valve member engages the valve seat so that the valve seat closes the first end of the tubular valve member, and an open position in which the first end of the valve member is spaced from the valve seat; wherein the tubular valve member leads from its first end to a second port (36) of the valve outside the chamber.
2. A valve as claimed in claim 1, further including: actuating means (38,46,54,56) operable to move the tubular valve member so that the first end thereof moves between the closed and open positions.
3. A valve as claimed in claim 2, wherein: the actuating means includes a solenoid (38) which can be actuated to move the tubular valve member so that the first end thereof moves from one of the closed and open positions to the other of those positions.
4. A valve as claimed in claim 3, wherein: the actuating means includes a resilient element (46,54,56) arranged to urge the tubular valve member in the opposite direction to the solenoid.
5. A valve as claimed in claim 3 or 4, wherein: the solenoid is mounted inside the chamber.
6. A valve as claimed in any of claims 3 to 5, wherein: the tubular valve member acts as an armature (40) of the solenoid and passes through a stator of the solenoid.
7. A valve as claimed in any preceding claim, further including: sealing means (50,52,54) for sealing the tubular valve member to a wall of the chamber such that the valve member can move relative to the chamber.
8. A valve as claimed in claim 7, wherein: the sealing means comprises an 0-ring (50) or the like sliding seal.
9. A valve as claimed in claim 7, wherein: the sealing means comprises a flexible diaphragm (52).
10. A valve as claimed in claim 7, wherein: the sealing means comprises a variable length hose (54).
11. A valve substantially as described with reference to the drawings.