Flowserve VTP Wet Pit - Manual (Page 46)

VERTICAL TURBINE PUMPS (VTPS) CENTRIFUGAL PUMPS ENGLISH 71569224 – 10-13
Page 46 of 76 flowserve.com
Pump and motor bearing temperature 5.8.4
If the pumps are working in a potentially
explosive atmosphere, temperature or vibration
monitoring at the bearings is recommended.
If pump bearing temperatures (such as thrust
bearings) are to be monitored it is essential that a
benchmark temperature is recorded at the
commissioning stage and after the bearing
temperature has stabilized.
 Record the bearing temperature (t) and the
ambient temperature (ta)
 Estimate the likely maximum ambient
temperature (tb)
 Set the alarm at (t+tb-ta+5) C [(t+tb-ta+10) F]
and the trip at 100 C (212 F) for oil lubrication
and 105 C (220 F) for grease lubrication
It is important, particularly with grease lubrication, to
keep a close watch on the bearing temperatures.
After startup the temperature rise should be gradual,
reaching a maximum after approximately 1.5 to 2
hours. This temperature rise should then remain
constant or marginally reduce with time.
Multiple Can Pump Operation 5.8.5
Additional procedures may be required in multiple
can pump systems when one or more pump remains
idle. Contact Flowserve for details.
Stopping and Shutdown 5.9
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) Switch off flushing and/or cooling/heating liquid
supplies at a time appropriate to the process.
For prolonged shutdowns 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.
Hydraulic, mechanical and electrical 5.10
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 is 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 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.
5.10.5 Pumped flow
Flow must not fall outside the minimum and
maximum continuous safe flow shown on the pump
performance curve and or data sheet.