PURPOSE: To provide sufficient control performance even when the water demand has reduced, by performing ON-OFF operation of pump through a low water demand detection sensor comprised of a pressure sensor and flow sensor for commanding deceleration.
CONSTITUTION: After starting a speed change motor M and pump P with minimum speed Nmin, the open-close decision of a high pressure side pressure sensor PSH is executed and if it is opened the waiting time (t) is provided to provide sufficient starting frequency and after executing the waiting time, the open- close decision of the high pressure side pressure sensor is executed again while if it is closed the speed change motor M and the pump P are stopped. If it is not opened, it is jumped to next step under the continuously operating state, thereby sufficient control characteristic is achieved even when the water demand has reduced.
MITA YASUHIRO
TAGAWA YUKIO
