... discharging 3-way valve,first,second change valve(N.O,N.C solenoid valve)and first water discharging stop ... water monitor would transmit alarm signal,change valve(N.O,N.C solenoid valve)operating,first stage discharging water ... way valves,drive piston downward,close the N.O port,open the N.c port,bilge water enter into the ... .Sea water(F.W)enter pump suction through N.C port from pump outlet,to be back ...