Flowserve MP1 Sier-Bath - Manual (Page 25)

MP1 USER INSTRUCTIONS ENGLISH 26999958 – 10-12
Page 25 of 48 flowserve.com
Where duty and standby pumps are installed it is
recommended that they are run alternately every
week.
5.10 Stopping and shutdown
5.10.1 Short term
a) Never close the outlet valve prior to
stopping the pump. Stop the driver.
b) Leave open the valve supplying auxiliary sealing
fluid to maintain prime while the pump is idle.
c) On pumps with steam jacketed bodies and/or
stuffing boxes, maintain steam flow to prevent
pumping liquid from setting up in the internals of
the pump.
5.10.2 Long term
a) Never close the outlet valve prior to
stopping the pump. Stop the driver.
b) Switch off flushing and/or cooling/heating liquid
supplies at a time appropriate to the process.
c) On pump with steam jackets, shut off steam flow
and allow pump to cool.
d) 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.
5.11 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 decide how to evaluate the implications
of any change. If in doubt contact your nearest
Flowserve office.
5.11.1 Differential pressure
Each operator should study the performance curve
supplied with the particular unit in question. This curve
should indicate the design pressure, capacity, speed
and viscosity (condition of service, COS, pumping
conditions) for which the unit was sold.
Figure 6 – D.P. vs. capacity relationship
Any positive displacement pump is suitable for a wide
range of operating conditions, but to meet a specific
condition of service the pumping rotors must be the
correct pitch and rotate at the correct speed. When the
rotor pitch, speed and viscosity are known, a single
curve can be drawn which shows the relationship
between differential pressure and capacity (Refer to
Figure 6). Barring suction, system or mechanical
troubles, the pump will operate at some point on this
curve.
To operate at some point not on the capacity-
differential pressure curve would require a different
speed or a different viscosity liquid being pumped.
A positive displacement pump has a general
characteristic that the flow decreases as the differential
pressure across the pump increases. The pump
operates against the resistance of the system and
does not generate head as a centrifugal pump does. It
will continue to operate if the system resistance
increases (closing of discharge valve), building up
internal pressure until failure of pressure containing
parts. A suitably sized relief valve should be present in
the discharge piping between the discharge valve and
the pump.
Again, it should be noted that a positive displacement
pump should never be started against a closed
discharge valve nor should the discharge valve be
closed prior to stopping the pump.
The capacity the pump produces at zero differential
pressure
(system resistance) is called the
displacement of the pump and is not dependent on the
viscosity of the liquid. It is a function of the size of the
pump, the pitch of the pumping rotors and the pump
speed. As the differential pressure increases,
recirculation or slip is produced as liquid is forced back
to suction through the internal clearances of the pump.
The slip increases proportionally to the differential