Valve assembly
A valve assembly including a housing and a first movable member which divides the housing into a control chamber and a main chamber. A second movable member has a first valve part and a second valve part and is movable to engage the first valve part with a corresponding inlet valve part to substantially prevent flow of fluid into the main chamber via an inlet port. The first movable member is provided with an exhaust valve part and is movable to engage the second valve part of the second movable member to substantially prevent flow of pressurized fluid out of the main chamber via an exhaust port. A support part is secured relative to the housing, there being a first seal between the second movable member and the support part and a second seal between the support part and the first movable member.
1. A valve assembly including a housing and a first movable member which divides the housing into a control chamber and a main chamber, the housing being provided with an inlet port, a delivery port and an exhaust port which connect the main chamber with the exterior of the housing, the valve assembly further including a second movable member which has a first valve part and a second valve part and which is movable parallel to an axis of the valve assembly to engage the first valve part with a corresponding inlet valve part secured relative to the housing, engagement of the first valve part with the inlet valve part substantially preventing flow of fluid into the main chamber via the inlet port, the first movable member being provided with an exhaust valve part and movable so that the exhaust valve part engages with the second valve part of the second movable member, engagement of the exhaust valve part with the second valve part initiating closing of the exhaust port, closing of the exhaust port substantially preventing flow of pressurized fluid out of the main chamber via the exhaust port, characterized in that the valve assembly is further provided with a support part, there being a first seal between the second movable member and the support part and a second seal between the support part and the first movable member.
2. The valve assembly according to claim 1 wherein the support part is fixed relative to the housing.
3. The valve assembly according to claim 1 wherein the valve assembly is provided with a third seal which provides a substantially fluid tight seal between a portion of the housing around the exhaust port and the second movable member so that fluid in the main chamber can only flow through the exhaust port via an aperture provided in the second movable member.
4. The valve assembly according to claim 1 wherein the inlet valve part is provided on a tubular extension which extends through an aperture provided in the first movable member and provides a conduit for flow of fluid from the supply inlet to the main chamber.
5. The valve assembly according to claim 4 wherein the valve assembly is provided with a fourth seal between the first movable member and the tubular extension.
6. The valve assembly according to claim 5 wherein the areas enclosed by the second seal and fourth seal are equal.
7. The valve assembly according to claim 6 wherein the areas enclosed by the second seal, third seal and fourth seal are equal.
8. The valve assembly according to claim 6 wherein the area enclosed by the third seal is greater than the areas enclosed by the second and fourth seals.
9. The valve assembly according to claim 6 wherein the area enclosed by the third seal is less than the areas enclosed by the second and fourth seals.
10. The valve assembly according to claim 7 wherein the second seal, third seal and fourth seal all form circles.
11. The valve assembly according to claim 8 wherein the second seal, third seal and fourth seal are arranged coaxially about the axis of the valve assembly.
12. The valve assembly according to claim 3 wherein the area enclosed by the line of contact between the exhaust valve part and the second valve part of the second movable member is greater than the area enclosed by the third seal.
13. The valve assembly according to claim 4 wherein the area enclosed by the first seal is less than the area enclosed by the second, third and fourth seals.
14. The valve assembly according to claim 1 wherein the area enclosed by the first seal is substantially identical to the area enclosed by the points of contact between the inlet valve part and the first valve part of the second movable member.
15. The valve assembly according to claim 1 wherein the support part is supported on a mounting part which is located in the exhaust port.
16. The valve assembly according to claim 15 wherein the support part includes a rod part, a first end of which is secured to the mounting part, a reaction piston being provided on the second end of the rod part.
17. The valve assembly according to claim 16 wherein the reaction piston has a first part which provides the first seal and a second part which provides the second seal.
18. The valve assembly according to claim 1 wherein the valve assembly further includes at least one electrically operable valve to control flow of fluid into and/or out of the control chamber.
19. The vehicle braking system including a source of pressurized fluid, a fluid pressure operated brake actuator and a valve assembly according to claim 1 wherein the inlet port of the valve assembly is connected to the source of pressurized fluid, and the delivery port of the valve assembly is connected to the brake actuator.