Doc No: OMM50002312
Rev: C Page 12 of 54
Subject to contractual terms and conditions to the contrar
y, this document and all the information contained herein are the confidential and exclusive
property of FMC Technologies, and may not be reproduced
, disclosed, or made public in any manner prior to express written authorization by FMCTI.
4.3 Suction Piping Recommendations
Poor suction piping practices are a very common source of pump problems. To ensure
proper operation it is very important to follow good design practice in the installation of
the suction system before the pump is operated. A small amount of additional planning
and investment in the piping system usually provides for better pump performance and
longer periods between service requirements. It is difficult to diagnose many pump
problems without the aid of a suction pressure gage. For this reason, FMC recommends
that a gage is always installed in the suction line directly before it enters the pump.
The suction line from the fluid source to the pump should be as short and direct as
possible. Use rigid piping, non-collapsible hose or a combination of both as
circumstances require in your installation. The suction pipe size should be at least equal
to or one size larger than the pump inlet. Long piping runs, low suction heads, or
indirect pipe routing may require even greater over-sizing of the suction line for proper
operation of the pump. A suction pulsation dampener is recommended to reduce the
effects of acceleration head to help when suction conditions are not optimal. In some
cases, it may be necessary to install a booster pump in the suction line to obtain
sufficient pressure for the pump to operate satisfactorily.
The suction line must be configured so there are no high spots in the line where air
pockets can collect. These pockets may make the pump difficult to prime and cause
rough, erratic operation. A drain valve or plug should be installed at the low point of the
suction line to allow for draining before freezing conditions or for maintenance.
FMC recommends that all piping is supported independently of the pump. By supporting
the piping this way, vibrations are reduced and stress on the pump is kept to a
minimum. The use of elbows, nipples, unions, or other fittings should be minimized.
Make sure that all joints and connections are airtight. Air leaks reduce the capacity of
the pump and can result in cavitation, rough operation, and/or loss of prime. To help
isolate mechanical and hydraulic vibrations, FMC recommends the use of flexible pipe
couplings or hose connections between the pump and any rigid piping.
Always ensure that calculated system Net Positive Suction Head available, NPSHa,
exceeds pump Net Positive Suction Head required, NPSHr, by at least 5 feet (1.5
meters) of water for proper operation of the pump. NPSH requirements for each pump
model are provided on the product data sheets available through FMC or your
authorized FMC reseller. FMC does not recommend using the pump in static lift
conditions without prior factory approval.
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