Pump Priming System

FOOT VALVES
A foot valve is a form of check valve installed at the bottom, or foot, of a suction line.When the pump stops and the ports of the foot valve close, the liquid cannot drain back to the suction well if the valve seats tightly. Foot valves were very commonly used in early installations of centrifugal pumps. Except for certain applications, their use is now much less common.

PRIMING CHAMBERS
Chamber primer is a tank with a bottom outlet thatis level with the pump suction nozzle and directly connected to it. An inlet at the top of the tank connects with the suction line. The size of the tank must be such that the volume contained between the top of the outlet and the bottom of the inlet is approximately three times the volume of the suction pipe. When the pump is shut down, the liquid in the suction line may leak out, but the liquid in the tank below the suction inlet cannot run back to the supply. When the pump is started, it will pump this entrapped liquid out of the priming chamber, creating a vacuum in the tank. The atmospheric pressure on the supply will force the liquid up the suction line into the priming chamber.

PRIMING INDUCTORS
If a separate source of liquid of sufficient capacity and pressure is available, it can be used to fill the suction line of the pump to be primed through the use of an inductor. For water, the pressure must be equal to about 4 lb/in2 for each foot (90 kPafor each meter) of head necessary to prime the pump, measured from the lowest liquid level in the sump from which priming must be accomplished to the top of the pump. The amount of liquid necessary depends on the pressure.

CENTRAL PRIMING SYSTEMS
If there is more than one centrifugal pump to be primed in an installation, one priming device can be made to serve all the pumps. Such an arrangement is called a central priming system. If the priming device and the venting of the pumps are automatically controlled, the system is called a central automatic priming system.