Specifications

156

case. This air / water separation is what makes the self primer different. Although the self

priming centrifugal pump will remove all air from its suction piping, it will not “dry prime”. The

pump case must be filled with water before starting. The foot valve, used at the bottom end of

suction pipe should withhold water in the suction pipe. The should be no leakage of water from

the foot valve. Also, there must be a way for the air to escape the discharge of the pump. If the

discharge piping is not open to atmosphere, an air release valve must be installed.

14.11 Automatic operation of a pump

A pumping installation can be easily wired for automatic control by installing a float switch

on the High Level storage tank. This ensures that the pump is started when the water level falls

down to, say, half the tank and automatically stopped when the tank becomes full. The only thing

to be ensured is that the pump is kept fully primed always. Therefore, the suction system and

the foot valve should be well maintained so that water is retained by the valve for long periods

and the pipe joints are air tight so that no air may leak in. One condition which should be always

ensured is that water level in the well should not fall below the foot valve. This can be taken care

by providing a low-level float switch in the well, arranged to cut off the power supply to the motor,

if the water level falls unduly in the well. Quite often pumps are unattended for long periods.

Where pumps are not working continuously and are likely to be off for long periods, it is best to

ensure priming of the pump before the pump is started.

14.12 Troubles Shooting

Troubles with centrifugal pumps and remedies

Maintaining case histories and statistical records of all installations will be very much useful

in trouble shooting. While investigating troubles, proceed from the most probable reason to the

least possible.

(a) Failure to start : Gland packing may be too tight. Check whether spindle is freely rotating.

Motor is not getting electric supply. Check voltage at the motor terminals and the mains.

Connections may not be tight (if starters used check relevant connections like star delta starters).

Check for loose connections.

(b) Failure to deliver water: Check if pump is properly primed and delivery valve/s is open.

Check suction valve if provided. Check if water level in the well is above the foot valve. Check

speed, it may be too low. Foot valve or suction line may be leaking. Foot valve strainer or impeller

may have become clogged up. If installation is new, the pump installed may not be the right one.

Note the suction and delivery gauge readings and check against the Maker’s characteristic

curves and installation data. If the pump is erected after overhaul one of the pipe joints may have

been improperly connected or wrongly connected.

Foot valve and impellers may have become clogged and neck rings badly worn out probably

due to working for a long time. Pump to be overhauled. Check for leaks on the delivery line.