CPX, CPXR, CPXN and CPXP USER INSTRUCTIONS ENGLISH 71569117 02-10
Page 14 of 44
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1) The discharge pipework regulating valve, if fitted,
may be partly opened during the priming cycle to
freely vent the air.
2) An automatic air release valve may be fitted to the
discharge pipework, between the pump and any
valves, providing that gases and vapours given off
are environmentally safe and acceptable for
release into the atmosphere.
3) An air bleed pipe may be run from the discharge
pipework, between the pump and any valves, back
to the suction tank or sump. This arrangement will
require a manual or automatic control during normal
operation to prevent continuous re-circulation of the
pumped liquid.
4.6.2 Suction piping
4.6.2.1 CPX, CPXR and CPXN suction piping
a) 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.
b) On suction lift the piping should be inclined up
towards the pump inlet with eccentric reducers
incorporated to prevent air locks.
c) On positive suction, the inlet piping must have a
constant fall towards the pump.
d) The pipe next to the pump should be the same
diameter as the pump suction and have a minimum
of two pipe diameters of straight section between
the elbow and the pump inlet flange. Where the
NPSH margin is not large, it is recommended that
the pipe straight is 5 to 10 pipe diameter. (See
section 10.3, Reference 1.) Inlet strainers, when
used, should have a net 'free area' of at least three
times the inlet pipe area.
e) Fitting isolation and non-return valves will allow
easier maintenance.
f) Never throttle pump on suction side and never
place a valve directly on the pump inlet nozzle.
4.6.2.2 CPXP suction piping
a) The inlet pipe should be as short as possible,
airtight and the smallest volume as practical for the
pump flow rate so as to be able to prime in quickly.
Where inlet pipe volume is large an inlet ball-foot
valve or flap valve will be required.
b) It is recommended that the pump inlet pipe is no
larger than the pump inlet bore or such that the
suction velocity is in the range of 3 to 5 m/sec
(10 to 16 ft/sec). The piping should slope down
towards the pump casing suction flange.
c) Allow a minimum of two pipe diameters of straight
section between the elbow and inlet flange.
d) Fitting an isolation valve will allow easier
maintenance.
e) Never throttle pump on suction side and never
place a valve directly on the pump inlet nozzle.
4.6.3 Discharge piping
4.6.3.1 CPX, CPXR and CPXN discharge piping
a) 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.
b) Fitting an isolation valve will allow easier
maintenance.
4.6.3.2 CPXP discharge piping
a) 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 discharge. Typically main pipework velocities
should not exceed 3 m/s (9 ft/sec) on the discharge.
Pipework expanders should have a maximum angle
of divergence of 9 degrees.
b) If a non-return valve is located in the discharge
pipework then a vent/bleed pipe should be fitted
from the discharge pipe back to the sump or
source tank.
c) A regulating valve should be fitted in the discharge
pipework unless pump flow is controlled by the
delivery system design.
4.6.4 Auxiliary piping
The connections that are to be piped
up will have been fitted with protective metal or
plastic plugs which will need to be removed.
4.6.4.1 CPX, CPXR and CPXN pumps fitted with
packed glands
When suction pressure is below ambient pressure
and differential head is less than 10 m (32.8 ft), it may
be necessary to feed gland packing with liquid to
provide lubrication and prevent the ingress of air.
4.6.4.2 Pumps fitted with mechanical seals
The conical design of the cover provides excellent
liquid circulation around the seal and will not normally
require a separate flush for single internal seals.
Single seals requiring re-circulation will normally be
provided with the auxiliary piping from pump casing
already fitted.
