The sensitivity of hydraulic devices to dirt is determined by the interaction between functional gaps and the particle size of the solid dirt. In doing so, a distinction must be made between hard and soft particles. While soft particles simply clog gaps, the hard particles also cause scoring and wear on the sliding areas.
This primarily involves particles of around the size of the gap: they can score the sliding surfaces, while the larger particles gather in front of the gap and the smaller particles are carried along.
Increasing the gap under pressure has a particularly unfavourable effect: Particles that enter the gap are clamped in place when the pressure is released.