The pump body adopts a round valve with special structure, which is opened when the outlet pressure is higher than the working pressure. Then, some medium will return to the inlet of the pump or storage tank through this annular valve. At the same time, the pump can be started under full pressure, thus greatly reducing torque.

The special design shall be adopted for the import and export civilization to ensure that there is enough medium left in the pump. Even if all the medium in the suction pipe is discharged, the pump still has good self-priming performance.