also is insurance against damage due to running the pump against a closed discharge valve or
very low flow conditions.
3.
Bearing temperature relay which will shut the unit down if the bearing temperature exceeds a
predetermined maximum.
4.
Low suction pressure control which will shut off the unit should the suction pressure drop below a
pre-established minimum. A centrifugal pump should never be throttled for capacity adjustment
on the suction side.
5.3 Operating at reduced head
On motor driven pumps, when discharge head or pressure is allowed to drop considerably below the rat-
ed point for any length of time, the motor should be watched for heating because the pump capacity in-
creases with reduced head, as does horsepower consumption. If this condition is likely to persist, ar-
rangements should be made either to manually or automatically throttle the discharge valve to build up
head to a safe point.
5.4 Operating with surge conditions in line
If a pump is installed with a quick closing valve in discharge line that doses when pump is running, dan-
gerous pressure surges may be built up that can cause damage to the pump or line. In services of this
kind, some cushioning arrangement must be provided to protect the pumping equipment.
5.5 Operating under freezing conditions
When exposed to freezing conditions and pump is standing idle, liquid inside the pump should be
drained by removing drain plugs in bottom of casing and opening air cocks at top. Liquid inside cooling
jackets or glands should also be drained.
5.3 Operating at reduced head
3107 Installation, Operation and Maintenance Instructions
35
