Goulds Pumps 3996 - IOM - Manual (Page 22)

SUCTION PIPING
s
! CAUTION
NPSH
A
must always exceed NPSH
R
as shown on
Goulds performance curves received with order.
(Reference Hydraulic Institute for NPSH and pipe
friction values needed to evaluate suction piping).
$
CAUTION
Pump must never be throttled from suction side.
Properly designed and installed suction piping is a
necessity for trouble-free pump operation. Suction piping
should be flushed BEFORE connection to the pump.
1. Use of elbows close to the pump suction flange
should be avoided. There should be a minimum of
two (2) pipe diameters of straight pipe [five (5) pipe
diameters is preferred] between the elbow and
suction inlet. Where used, elbows should be long
radius.
2. Use suction pipe one (1) or two (2) sizes larger than
the pump suction, with a reducer at the suction
flange. Suction piping should never be of smaller
diameter than the pump suction.
3. Reducers, if used, should be eccentric and located at
the pump suction flange with sloping side down.
4. A suction screen should be installed prior to initial
start-up and when suction system has been opened
for work. The screen should be of the cone type with
a net area equal to at least three (3) times the cross
sectional area of the suction pipe. The mesh of the
screen should be sized to prevent particles larger than
1.6 mm (1/16 in.) from entering the pump and should
be installed in a spool piece to allow removal for
cleaning. The screen should remain in the system
until periodic inspection shows system is clean.
5. Separate suction lines are recommended when more
than one pump is operating from the same source of
supply.
Suction Lift Conditions
1. Suction pipe must be free from air pockets.
2. Suction piping must slope upwards to pump.
3. All joints must be air tight.
4. A means of priming the pump must be provided.
Suction Head/Flooded Suction Conditions
1. An isolation valve should be installed in the suction
line at least two (2) pipe diameters from the pump
suction to permit closing of the line for pump
inspection and maintenance.
2. Keep suction pipe free from air pockets.
3. Piping should be level or slope gradually downward
from the source of supply.
4. No portion of the piping should extend below pump
suction flange.
5. The size of entrance from supply should be one (1) or
two (2) sizes larger than the suction pipe.
6. The suction pipe must be adequately submerged
below the liquid surface to prevent vortices and air
entrainment at the supply.
DISCHARGE PIPING
Properly designed and installed discharge piping is a
necessity for trouble-free pump operation. Discharge
piping should be flushed BEFORE connection to
the pump.
1. Isolation and check valves should be installed in
discharge line. Locate the check valve between
isolation valve and pump; this will permit inspection
of the check valve. The isolation valve is required
for priming, regulation of flow, and for inspection
and maintenance of pump. The check valve prevents
pump or seal damage due to reverse flow through the
pump when the driver is turned off.
2. Increasers, if used, should be placed between pump
and check valves.
3. Cushioning devices should be used to protect the
pump from surges and water hammer if quick-closing
valves are installed in system.
BYPASS PIPING
Systems that require operation at reduced flows for
prolonged periods should be provided with a bypass line
connected from the discharge side (before any valves) to
the source of suction.
A minimum flow orifice can be sized and installed in
bypass line to preclude bypassing excessive flows.
Consult nearest sales office or factory for assistance in
sizing orifice.
An automatic recirculation control valve and/or solenoid
operated valve should be considered if a constant bypass
(i.e. orifice) is not possible.
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3996 IOM 9/2010
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