In either of these methods (1) and (2) , the pump will remain primed, provided foot valve is tight.
Any failure, however, of foot valve when pump is standing idle, will permit the pump to lose its
prime. During long idle periods, the pump can also lose its prime through leakage from stuffing
boxes.
The valve in bypass can be left open, in which event, during idle periods, loss through foot valve
is constantly replenished from discharge line. This system is used for automatic operation where
idle periods are of short duration and there is no danger of exhausting all liquid from discharge
line, due to a leaky foot valve. The foot valve must be capable of withstanding static head pres-
sure of the system.
3.
Bypassing Around Discharge Check Valve
This method can be used only when there is liquid under some pressure in the discharge line.
The original prime must be effected from some outside source. After subsequent idle periods,
open air vent valves and open valve in bypass line around discharge check and gate valves until
liquid flows from air vent openings. Close air vent valves and bypass valve, start pump and open
discharge gate valve.
Figure 26:
Priming by ejection
On suction lift installation, an ejector, operated by steam, compressed air, or water under pressure, and
connected to tapped opening in top of casing can be used to remove air from casing and suction line,
thus priming the pump. See Fig. 27.
Close discharge gate valve, open valve "E'' in steam, air or water pressure supply line. Open valve "S" in
suction pipe of ejector connected to pump casing. Air will be evacuated and liquid will be drawn up into
suction pipe and pump casing. When all air is evacuated, start pump, dose valve "S" and valve "E", and
open discharge gate valve.
4.3 Priming
30
3107 Installation, Operation and Maintenance Instructions
