PURPOSE: To allow a pump to start idle and also to facilitate cleaning by designing the water ring pump to a vertical type instead of vane type, arranging a lower discharge/drain part joining with an upper discharge part outside the pump and mounting it on the bottom of a casing, free from riser and kept open at all times.

CONSTITUTION: A synthetic casing and horizontal pump is designed to a vertical type straight as it is; when a pump runner 3 stops running, operating water in a casing 1 is drained away outside the pump by way of a lower discharge/drain part 9 which is kept open at all times. The pump is therefore ready for starting idle. From feeding necessary quantity in the pump, the operating water circulates in the casing 1 along its inner periphery according to a running of the runner 3 and operates as in the case of normal pumps. Thus the pump can be activated smoothly without shock or vibration, the runner can be prevented from being damaged and a starting torque can further by minimized.