PURPOSE: To prevent the idling even when there is no supply of the liquid, by monitoring the flow between a pressurizing pump and a liquid feeder/receiver then controlling said pump such that said flow will come within the predetermined range.

CONSTITUTION: The pressure P and the flow Q in a piping 15 in front of a liquid feeder/receiver 16 are same with those in a pressure monitor system if the pump is not pressurized but varies on a curve 27, and under the latching state P and Q will move on the curve 21 to the right upon opening of a flow regulation valve 17 then a pressurizing pump 9 will start at the point A' while when P and Q move over the curve 43 to reach to the point B', it will move over the curve 22 upon the opening/closing of the valve 17 while when the valve 17 is reduced to reach to the point C' the pressurizing pump 9 will stop to reach to the point D' and when reaching to the point C' where Q is decreased to the setting flow 42 said pump 9 will stop, thereby it will move over the pressure loss curve 46 to reach to the point D' thus to control the pressure drop normally. When the liquid feed capacity in the conduit will deteriorate (For example the curve 49.), the flow will increase only to the cross point 50 even if the valve 17 is fully open thereby the pump will never function.