Valves regulate the flow in a fluid system.Small particles, especially those of approximately clearance size, can wedge themselves between the surfaces in the valve.When clearance-size particles become wedged in this way, the valve requires an additional amount of force to move.Eventually this stiction can actually lock the valve in place, potentially causing a system failure.
案例研究：Valve Shifting Force vs.Contamination in Fluid
Conditions of directional valve:
About 15 gpm, 3000 psi
Radial clearance, 8µm
Valve held stationary and under pressure before shifting force was measured.
The study illustrates that the force required for valve shifting is greatest when challenged by particles in the operating clearance size range.Valve clearances will exclude the larger particles and are less sensitive to the smaller ones.The conclusion is that particles in the clearance size range will be caught in the clearance space and thereby require greater force to get the valve to shift.