16
STOPPING
The pump may be stopped with the discharge valve open without causing
damage. However, in order to
prevent water hammer effects, the discharge valve should be closed first.
1. Close discharge valve.
2. Stop driver.
3. Close water seal valves.
4. Close valve in the pump suction line. If danger of freezing exists, drain
the pump completely.
Minimum operating Flow
;
All centrifugal pumps have limitations on the minimum flow at which they
should be operated. The most common limitation is to avoid excessive
temperature buildup in the pump because of absorption of the input
power into the pumped fluid. Other less understood reasons for
restrictions are:
1. Increased radial reaction at low flows in single volute casings.
2. Increased NPSHR at low flows.
3. Noisy, rough operation and possible physical damage due to internal
recirculation.
4. Increased suction and discharge pulsation levels.
5. The size of the pump, the energy absorbed, and the liquid pumped are
among the considerations in determining these minimum flow limitations.
For example, most small pumps such as domestic home circulators,
service water pumps and chemical pumps have no limitations, except for
temperature buildup considerations while many large, high horsepower
capacity.
