Flowserve CPXV fitted with Mark 3 ASME hydraulics - Manual (Page 23)

CPXV with Mark 3 ASME hydraulics ENGLISH 71569291 12-14
Page 23 of 44
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Where pumps operate in a hazardous area
refer to section 1.6.4.3 and 4.7 for the requirements
for monitoring and protective systems.
5.8.7 Shaft seal at sole plate
Seal maximum temperature to be defined by seal
vendor for that specific application.
5.8.8 Stop/start frequency
Pump sets are normally suitable for the number of
equally spaced stop/starts per hour shown in the
table below. Check capability of the driver and
control/starting system before commissioning.
Motor rating kW (hp)
Maximum stop/starts
per hour
Up to 15 (20) 15
Between 15 (20) and 90 (120) 10
Above 90 (120) 6
Where duty and standby pumps are installed it is
recommended that they are run alternately every week.
5.9 Stopping and shutdown
a) Close the outlet valve, but ensure
that the pump runs in this condition for no more
than a few seconds.
b) Stop the pump.
c) After stopping a jacketed pump,
leave the steam supply on for approximately 20
minutes. Keep steam circulating in stand-by
pumps.
d) Switch off flushing and/or cooling/heating liquid
supplies at a time appropriate to the process.
e) For prolonged shut-downs and
especially when ambient temperatures are likely to
drop below freezing point, the pump and any
cooling and flushing arrangements must be drained
or otherwise protected.
5.10 Hydraulic, mechanical and electrical
duty
This product has been supplied to meet the
performance specifications of your purchase order,
however it is understood that during the life of the
product these may change. The following notes may
help the user decide how to evaluate the implications
of any change. If in doubt contact your nearest
Flowserve office.
5.10.1 Specific gravity (SG)
Pump capacity and total head in metres (feet) do not
change with SG, however pressure displayed on a
pressure gauge is directly proportional to SG.
Power absorbed is also directly proportional to SG. It
is therefore important to check that any change in SG
will not overload the pump driver or over-pressurize
the pump.
5.10.2 Viscosity
For a given flow rate the total head reduces with
increased viscosity and increases with reduced
viscosity. Also for a given flow rate the power
absorbed increases with increased viscosity, and
reduces with reduced viscosity. It is important that
checks are made with your nearest Flowserve office if
changes in viscosity are planned.
5.10.3 Pump speed
Changing pump speed effects flow, total head, power
absorbed, NPSH
R
, noise and vibration. Flow varies
in direct proportion to pump speed, head varies as
speed ratio squared and power varies as speed ratio
cubed. The new duty, however, will also be
dependent on the system curve. If increasing the
speed, it is important therefore to ensure the
maximum pump working pressure and critical shaft
speed are not exceeded, the driver is not overloaded,
NPSH
A
> NPSH
R
, and that noise and vibration are
within local requirements and regulations.
5.10.4 Net positive suction head (NPSH
A
)
NPSH available (NPSH
A
) is a measure of the head
available in the pumped liquid, above its vapor
pressure, at the pump suction branch.
NPSH required (NPSH
R
) is a measure of the head
required in the pumped liquid, above its vapor pressure,
to prevent the pump from cavitating.
It is important that NPSH
A > NPSH
R
. The margin
between NPSH
A
> NPSH
R
should be as large as
possible.
If any change in NPSH
A
is proposed, ensure these
margins are not significantly eroded. Refer to the
pump performance curve to determine exact
requirements particularly if flow has changed.
If in doubt please consult your nearest Flowserve
office for advice and details of the minimum allowable
margin for your application.