During dispersion, solid particles in between the guiding surfaces of the pumps can lead to jamming of the movable closing unit. If solid particles are trapped, this prevents the complete closing of a valve. Thus, the fluid can flow back through the remaining gap. If the valve opens only slightly (e.g., with very small stroke lengths or high spring load), solid particles larger than the opening gap may not pass of i.e. a valve.
At low flow velocities (small stroke length, small stroke frequency), solid particles can be deposited in the flow dead spaces of the valve. The consequences of this are non-constant flow rate, increased wear, increase in pressure loss, reduced flow rate up to the failure of a pump.