Flowserve Pump Division - 13
DRY PIT INSTALLATION
Piping Strains
Satisfactory operation cannot be maintained when the piping imposes a force on the pump. Misaligned
piping flanges can spring and pull a pump out of position when their bolts are drawn up. Flanges must
have flat faces and be brought squarely together before the bolts are tightened. To avoid breaking the
flanges when tightening the bolting, mating pipe flanges should also have flat faces and full face gaskets
should be used. Suction and discharge pipes, and associated equipment, should be supported and
anchored near, but independent of the pump so that no strain will be transmitted to the pump casing.
CAUTION: PIPE COUPLINGS WHICH ARE NOT AXIALLY RIGID ARE SOMETIMES USED IN
THE DISCHARGE AND/OR SUCTION PIPING TO AVOID TRANSMITTING ANY
PIPING STRAINS CAUSED BY SYSTEM PRESSURE, THERMAL EXPANSION, OR
PIPE MISALIGNMENT. SUCH PIPE COUPLINGS ALLOW TRANSMITTAL TO THE
PUMP, A FORCE EQUAL TO THE AREA OF THE EXPANSION JOINT TIMES THE
PRESSURE IN THE PIPING. THESE FORCES CAN HAVE A SIGNIFICANT
MAGNITUDE AND IT IS IMPRACTICAL TO DESIGN THE PUMP CASING, SUPPORT,
ETC., TO WITHSTAND THEM. CONSEQUENTLY, WHEN PIPE COUPLINGS LACK
AXIAL RIGIDITY, A SUITABLE PIPE ANCHOR MUST BE INSTALLED BETWEEN IT
AND THE PUMP. ALTERNATELY, ADEQUATE RESTRAINING DEVICES SHOULD
BE USED AND PROPERLY ADJUSTED TO PREVENT THESE FORCES FROM
BEING TRANSMITTED TO THE PUMP.
Suction Piping
Experience has shown that the major source of trouble in centrifugal pump installations, other than
misalignment, is traceable to a faulty suction line. The utmost attention must be given to this portion of
the installation to ensure that the pump receives hydraulically stable flow. The suction piping should be
direct as possible and its length held to a minimum. If a long suction line is required, increase the pipe
size to reduce friction losses. Then gradually reduce the pipe size in steps before entering the pump.
The piping should be run without having high spots and should have a continual rise toward the pump.
This prevents air pockets which inevitably cause trouble. Clean out all debris from the suction line and
wet well prior to operating the pumps.
Care should be exercised to keep the suction piping air tight and sealed against leakage. An isolation
valve is recommended in the suction line if a positive head exists above the top of the casing. Isolation
valves on suction and discharge lines are recommended to facilitate future inspection and repairs.
Discharge Piping
A check valve and a gate valve are normally installed in the discharge line. The check valve is normally
placed between the pump and the gate valve to protect the pump from any excessive back pressure and
reverse rotation which may be caused by water running back through the pump casing during a driver or
power failure. Any reverse flow through the pump or excessive back pressure should be kept to an
absolute minimum. The check valve will also prevent suspended solids from accumulating in the casing
and will increase wearing ring life.
Instrumentation
A compound pressure gauge should be connected to the suction and a pressure gauge connected to the
discharge side of each pump. Mount the gauges at a convenient location as they are necessary for any
adequate check on pump performance.
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