Influence of hardness and particle load on leakage of hydraulic seat valves

Seat valves constitute the biggest part of hydraulic valves sold nowadays. Compared to spool valves, they provide the advantage of being able to isolate a hydraulic pressure nearly Without leakage. However, in certain applications any leakage whatsoever is prohibited. Therefore, efforts are carried Out to increase the tightness of metallic sealing. A test rig was designed and built to investigate valves made from steel with different values of surface hardness. They can be tested with varying hydraulic and mechanical parameters, Such as particle load of the oil. To adjust the contact force between piston and seat, an adjustable pressure supply is being used. A second adjustable high pressure supply, which provides pressures of 350 bar, is used to create leakage. To exclude influences of other seals oil the leakage, the flow is measured at the low pressure side of the seat. This paper presents the contact force depending leakage of three valves with different hardness. It is shown that I harder valve material requires higher contact forces to achieve acceptable tightness. Furthermore, the characteristic of leakage over time and its change with increasing particle load of the oil IS discussed.