The gap size of the water ring vacuum pump has a significant impact on the performance. The essence of this effect is the effect of gas leakage on pump performance, or the effect of volume loss or volumetric efficiency on pump performance.

The clearance of the water ring vacuum pump is divided into radial clearance and axial clearance.

Radial clearance means that when the water ring vacuum pump is working, the inner boundary of the water ring on the upper part of the pump body is not tightly attached to the contour, and there is a gap between them, so the gas in the compression chamber can leak into the suction chamber through this gap. This volume loss tends to be large, eg as high as 35-38% at 60% vacuum.

The existence of radial clearance will reduce efficiency, increase water consumption, work unevenly, and generate noise.

For axial single-acting pumps, the axial clearance refers to the end face clearance between the impeller and the pump body.

It can be seen that when the gap exceeds a certain value, the relative evacuation time required by the pump with the same axial gap is related to the required vacuum degree. For the same vacuum degree, the relative evacuation time increases with the increase of the axial gap.

Relative evacuation time is more important for fuel pumps and fire pumps. Ship water pumps and vacuum diversion devices of large and medium-sized pumping stations also have certain requirements for the relative evacuation time.