PURPOSE: To eliminate possibility of water supply interruption during backup operation for eventual failure in a water supply arrangement consisting of a plurality of pumps by driving pumps not with a variable speed driving means but with a direct power supply in the even of failure.
CONSTITUTION: In an arrangement in which No.1 pump 4-1 and No.2 pump 4-2 are alternately driven by a variable speed driving means INV, when excessive load is applied to either of the pumps, the corresponding thermal relay is actuated to close the contact TH1a or TH2a, and now the contact R1c of relay R1 is changed over from the (b) side to (a) side, to be connected with direct power supply according to position of the contact Z2c of an alternate relay Z2 so as to energize an electromagnetic contactor MC1 for putting the pump into operation. This provides perfect backup in the event of failure in the pumps with a quick rise, which assures free from generation of pressure drop.
MORIMOTO HIROSHI
ISHIDA SHINOBU
HAMANO FUKUO
INAGAKI MASANOBU
OGURA MICHIO
HITACHI KEIYO ENG