Goulds Pumps 3408A - IOM - Manual (Page 25)

Figure 10:
Unbalanced loading of a double suction impeller due to
uneven flow around an elbow adjacent to the pump.
When operating on a suction lift, the suction pipe should
slope upward to the pump nozzle. A horizontal suction line
must have a gradual rise to the pump. Any high point in the
pipe will become filled with air and thus prevent proper
operation on the pump. When reducing the piping to the
suction opening diameter, use an eccentric reducer with the
eccentric side down to avoid air pockets.
NOTE: When operating on suction lift, never use a
straight taper reducer in a horizontal suction line, as it
tends to form an air pocket in the top of the reducer
and the pipe.
To facilitate cleaning pump liquid passage without
dismantling pump, a short section of pipe (Dutchman or
spool piece), so designed that it can be readily dropped out
of the line, can be installed adjacent to the suction flange.
With this arrangement, any matter clogging the impeller is
accessible by removing the nozzle or pipe section.
Valves in Suction Piping
When installing valves in the suction piping, observe
the following precautions:
a.
If the pump is operating under static suction lift
conditions, a foot valve may be installed in the
suction line to avoid the necessity of priming
each time the pump is started. This valve should
be of the flapper type, rather than the multiple
spring type, sized to avoid excessive friction in
the suction line. (Under all other conditions, a
check valve, if used, should be installed in the
discharge line. See the section entitled Valves in
Discharge Piping.
b. When foot valves are used, or where there are
other possibilities of “water hammer,” close the
discharge valve slowly before shutting down the
pump.
c. Where two or more pumps are connected to the
same suction line, install gate valves so that any
pump can be isolated from the line. Gate valves
should be installed on the suction side of all
pumps with a positive suction pressure for
maintenance purposes. Install gate valves with
stems horizontal to avoid air pockets. Globe
valves should not be used, particularly where
NPSH is critical.
d. The pump must never be throttled by the use of
a valve on the suction side of the pump. Suction
valves should be used only to isolate the pump
for maintenance purposes, and should always be
installed in positions to avoid air pockets.
e. A pump drain valve should be installed in the
suction piping between the isolation valve and
the pump.
Discharge Piping
If the discharge piping is short, the pipe diameter
can be the same as the discharge opening. If the
piping is long, pipe diameter should be one or two
sizes larger than the discharge opening. On long
horizontal runs, it is desirable to maintain as even a
grade as possible. Avoid high spots, such as loops,
which will collect air and throttle the system or lead
to erratic pumping.
Valves in Discharge Piping
A triple duty valve should be installed in the
discharge. The triple duty valve placed on the pump
protects the pump from excessive back pressure, and
prevents liquid from running back through the pump
in case of power failure.
Pressure Gauges
Properly sized pressure gauges should be installed in
both the suction and discharge nozzles in the gauge
taps, provided on request. The gauges will enable
the operator to easily observe the operation of the
pump, and also determine if the pump is operating in
conformance with the performance curve. If
cavitation, vapor binding, or other unstable
operation should occur, widely fluctuating discharge
pressure will be noted.
Pump Insulation
On chilled water applications most pumps are
insulated. As part of this practice, the pump bearing
housings should not be insulated since this would
tend to trap heat inside the housing. This could lead
to increased bearing temperatures and premature
bearing failures.
3408A IOM 6/08
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