Liquid enters the meshing space volume under the action of pressure difference. When the volume increases to its maximum, forming a sealed cavity, the liquid continuously moves axially within each sealed cavity until it reaches one end of the discharge cavity. At this point, the meshing space volume of the screw at the discharge cavity gradually decreases, discharging the liquid.
The working principle of a three-screw pump is similar to that of a gear pump, except that a screw replaces the gears in its structure. The table shows the characteristics and applications of various screw pumps.
Three-screw pumps have very small flow and pressure pulsations, low noise and vibration, and self-priming capability, but the screw is more difficult to manufacture. Pumps are available in single-suction and double-suction structures, but single-screw pumps are only available in single-suction type. Three-screw pumps must be equipped with a safety valve (single-screw pumps do not need one) to prevent damage to the pump or prime mover due to reasons such as blockage of the discharge pipe causing the pump's outlet pressure to exceed the allowable value.
