To solve problems wherein (1) when an air pipe opening is provided in a lifting pipe (pump discharge side), if backflow of pumped water from the air pipe is jetted during original pump operation, this causes troubles of pumping and a facilities and (2) when the air pipe opening is provided in a draft pipe (pump suction side) and a pump is used for suction such as a hand pump, suction of air from the air pipe makes the suction effect impossible and prevents operation of the pump.

(1) A check valve is attached to an air pipe to prevent jetting of pressurized water by a pump. During stoppage, although temperature change and malfunction of a pump foot valve may cause suction of air from the air pipe through the check valve, since small amount of the air is sucked for a short time, this serves as mechanical relief. Since it is unnecessary to operate the check valve, it can be installed in the vicinity of an opening. Thus, if the air pipe is broken, effects on the original pump can be minimized. (2) A closing valve is attached to the air pipe. During operation of an auxiliary pumping system, the valve is opened to send air. When the auxiliary pumping system is not operated, the valve is closed to prevent suction of air.