A few things you should know about your pump's piping system
- There should be at least 10 diameters of pipe between the
suction of the pump and the first elbow. This is especially
critical in double-ended pump designs as the turbulent inlet flow
can cause shaft thrusting, and subsequent bearing problems. If an
elbow must be installed be sure it is in a plane at right angles
to the pump shaft to prevent an uneven flow to both sides of a
double suction impeller.
- Pipe from the pump suction flange to the pipe rack, not the
other way around.
- Make sure eccentric reducers are not installed upside down at
the pump suction. The top of the reducer should go straight into
the suction flange.
- Piping should be arranged with as few bends as possible. If
bends are necessary use a long radius when ever possible
- If an expansion joint is installed in the piping between the
pump and the nearest point of anchor in the piping, It should be
noted that a force equal to the area of the expansion joint (which
could be a lot larger than the normal piping size) times the
pressure in the piping will be transmitted to the pump proper.
Pipe couplings that do not provide an axially rigid connection
have the same affect. If an expansion join or non-rigid coupling
must be used, it is recommended that a pipe anchor be installed
between it and the pump.
- Be aware that radial forces are being generated in the pump
housing from the pressure in the piping system acting on the
volute area. The magnitude and direction of the forces is
dependent upon the piping arrangement along with the areas and
- It is always a good idea to increase the size of the suction
and discharge pipes at the pump nozzle in order to decrease the
head loss from pipe friction.
- Suction piping should be at least one size larger than the
suction flange at the pump.
- If increasers are used on the discharge side to increase the
size of discharge piping, they should be installed between the
check valve and the pump.
- Both a check and gate valve should be installed in the
discharge piping with the check valve placed between the pump and
the stop valve to protect the pump from reverse flow and excessive
back pressure. Manually operated discharge valves that are hard to
reach should have some facility for quick closing. A sprocket rim
wheel and chain or a remotely operated motor are two alternatives
you might consider.
- Suction piping must be kept free of air leaks.
- The installation of check valves should be avoided in the
suction piping although they are often used to reduce the number
of valves that have to be operated in switching between series and
parallel pump operation.
- A foot valve is often installed in the suction piping to aid
priming. Do not install them if the pump is operating against a
high static head because failure of the driver would allow liquid
to rush back suddenly causing water hammer. This is especially
true for vertical turbine and submersible pumps that are not
designed for use with a foot valve.
- Foot valves should be of the low loss flap type rather than
the multiple spring variety and have a clear passage for the
liquid at least the same area as the suction piping.
- A horizontal suction line should have a gradual rise or slope
to the pump suction.
- Cast iron pumps should never be provided with raised face
flanges. If steel suction or discharge piping is used, the pipe
flanges should be of the flat face type and not the raised face
type. Full-faced gaskets must be used with cast iron flanges.
- The optimum control valve location is within five feet (1,5
meters) of the pump discharge to prevent too much surging of fluid
in the system when the discharge is throttled.
- The optimum pipe size will consider the installed cost of the
pipe (the cost increases with size) and the pump power
requirements (the power required increases with pipe friction)
- Try to limit the friction loss at design flow to 2-5 feet
for each 100 feet (1-2 meters for each 30 meters) of
- To prevent the settling of solids you need a minimum
velocity of about 4 to 7 feet per second (1.5 to 2.5 meters per
- Velocities of no more than 10 feet (3 meters) per second
are recommended in the suction side piping to prevent abrasive
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