Flowserve PHL - Manual (Page 19)

PHL USER INSTRUCTIONS ENGLISH 00079593 – 10/10
Page 19 of 31
5.10 Stopping and shutdown
a) Close the outlet valve, but ensure
that the pump runs in this condition not longer
than a few seconds.
b) Stop the pump.
c) Switch off flushing and/or cooling/heating liquid
supplies at a time appropriate to the process.
d) For longer 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.
5.11 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 to decide how to evaluate the
implications of any change. If in doubt, contact your
nearest Flowserve office.
5.11.1 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.
5.11.2 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.
5.11.3 Pump speed
Changing pump speed effects flow, total head, power
absorbed, NPSH
R
, noise and vibration. The flow is
directly proportion of the 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 is not exceeded, the driver is not
overloaded, NPSH
A
> NPSH
R
, and that noise and
vibration are within local requirements and regulations.
5.11.4 Net positive suction head (NPSH
A
)
NPSH available (NPSH
A
) is a measure of the head
available in the pumped liquid, above vapour
pressure, at the pump suction branch.
NPSH required (NPSH
R
) is a measure of the head
required in the pumped liquid, above its vapour
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.
5.11.5 Pumped flow
Flow must not fall outside the minimum and
maximum continuous safe flow shown on the pump
performance curve and or data sheet.