Flowserve Gearex Rotary Gear Pumps External and Internal Bearing - Manual (Page 26)

EXTERNAL GEAREX USER INSTRUCTIONS ENGLISH 71569246 (2167B-E1)
Flowserve Pump Division 26
®
4.7 Piping
Protective covers are fitted to the pipe
connections to prevent foreign bodies entering during
transportation and installation. Ensure that these
covers are removed from the pump before connecting
any pipes.
4.7.1 Suction and discharge pipework
In order to minimize friction losses and hydraulic noise
in the pipework it is good practice to choose pipework
that is one or two sizes larger than the pump suction
and discharge. Typically main pipework velocities
should not exceed 2 m/s (6 ft/sec) suction and 3 m/s
(9 ft/sec) on the discharge.
Take into account the available NPSH which must be
higher than the required NPSH of the pump.
Never use the pump as a support for
piping.
Maximum forces and moments allowed on the pump
flanges vary with the pump size and type. To
minimize these forces and moments that may, if
excessive, cause misalignment, hot bearings, worn
couplings, vibration and the possible failure of the
pump casing, the following points should be strictly
followed:
•
Prevent excessive external pipe load
•
Never draw piping into place by applying force to
pump flange connections
•
Do not mount expansion joints so that their force,
due to internal pressure, acts on the pump flange
Information regarding maximum allowable forces and
moments on the suction and discharge flanges is
provided on the General Arrangement drawing.
Suction and discharge piping and associated
equipment should be supported and anchored near to
but independent of the pump. If an expansion joint or
non-rigid coupling must be used, a pipe anchor must
be installed between it and the pump to ensure that
any flange loads do not exceed the specified limits.
If operational difficulties are encountered, suction and
discharge pressure readings must be determined to
establish the cause of the problem. In anticipation of
such problems, pressure taps, located in a straight
section of pipe between the pump and first fitting
should be provided on the suction and discharge
lines.
Ensure piping and fittings are flushed
before use.
Ensure piping for hazardous liquids is arranged
to allow pump flushing before removal of the pump.
4.7.2 Suction piping
a) The suction piping should be as short and as
direct as possible.
b) The inlet pipe should be one or two sizes larger
than the pump inlet bore and pipe bends should
be as large a radius as possible.
c) Pipework reducers should have a maximum total
angle of divergence of 15 degrees.
d) On suction lift the piping should be inclined up
towards the pump inlet with eccentric reducers
incorporated to prevent air locks.
e) On positive suction, the inlet piping must have a
constant fall towards the pump.
f) Flow should enter the pump suction with uniform
flow, to minimize noise and wear. This is
particularly important on large or high-speed
pumps which should have a minimum of four
diameters of straight pipe on the pump suction
between the elbow and inlet flange. See section
12.3 Additional sources of information
for more
detail.
g) Inlet strainers, when used, should have a net `free
area' of at least three times the inlet pipe area.
h) Do not install elbows at an angle other than
perpendicular to the shaft axis. Elbows parallel to
the shaft axis will cause uneven flow.
i) Except in unusual circumstances strainers are not
recommended in inlet piping. If considerable
foreign matter is expected a screen installed at
the entrance to the wet well is preferable.
j) Fitting an isolation valve will allow easier
maintenance.
k) Never throttle pump on suction side and never
place a valve directly on the pump inlet nozzle.
4.7.3
Discharge piping
A non-return valve should be located in the discharge
pipework to protect the pump from excessive back
pressure and hence reverse rotation when the unit is
stopped.
Pipework reducers should have a maximum total
angle of divergence of 15 degrees. Fitting an isolation
valve will allow easier maintenance.
4.7.4
Relief Valves
Gearex Pumps are of the positive displacement type
and will build up considerable pressure if discharge
line is blocked through closing of valve, etc. It is
therefore necessary for the protection of the pump
and discharge line to provide a relief valve. This