Flowserve Guardian Sealless Metallic - Manual (Page 34)

GUARDIAN USER INSTRUCTIONS ENGLISH 71569212 08-11
Page 34 of 68 flowserve.com
5.7 Starting the pump
a) Open the suction valve to full open position. It is
very important to leave the suction valve open
while the pump is operating. Any throttling or
adjusting of flow must be done through the
discharge valve. Partially closing the suction
valve can create serious NPSH and pump
performance problems.
Never operate pump with both the
suction and discharge valves closed. This could
cause an explosion.
b) Ensure the pump is primed. (See section 5.6.)
c) All cooling, heating, and flush lines must be
started and regulated.
d) Start the driver (typically, the electric motor).
e) Slowly open the discharge valve until the desired
flow is reached, keeping in mind the minimum
continuous flow listed in section 3.4.
It is important that the discharge
valve be opened within a short interval after
starting the driver. Failure to do this could cause
a dangerous build up of heat, and possibly an
explosion.
5.8 Running or operation
5.8.1
Minimum continuous flow
Minimum continuous stable flow is the lowest flow at
which the pump should be operated. The minimum
continuous flow (capacity) is established as a
percentage of the
best efficiency point (BEP). See
section 3.4.4.
5.8.2
Minimum thermal flow
All Guardian G & H series pumps also have a
minimum thermal flow. This is defined as the
minimum flow that will not cause an excessive
temperature rise. Minimum thermal flow is
application dependent.
Do not operate the pump below
minimum thermal flow, as this could cause an excessive
temperature rise. Contact a Flowserve Sales Engineer
for determination of minimum thermal flow.
Avoid running a centrifugal pump at drastically
reduced capacities or with discharge valve closed for
extended periods of time. This can cause severe
temperature rise and the liquid in the pump may
reach its boiling point. If this occurs, the internal
process-lubricated bearings will be exposed to vapor,
with no lubrication, and may be damaged or fail within
a very short period of time. Continued running under
these conditions when the suction valve is also
closed can create an explosive condition due to the
confined vapor at high pressure and temperature.
Thermostats may be used to safeguard against over
heating by shutting down the pump at a
predetermined temperature.
Safeguards should also be taken against possible
operation with a closed discharge valve, such as
installing a bypass back to the suction source. The
size of the bypass line and the required bypass flow
rate is a function of the input horsepower and the
allowable temperature rise.
5.8.3
Reduced head
Note that when discharge head drops, the pump’s
flow rate usually increases rapidly. Check motor for
temperature rise as this may cause overload. If
overloading occurs, throttle the discharge.
5.8.4
Surging condition
A rapidly closing discharge valve can cause a
damaging pressure surge. A dampening
arrangement should be provided in the piping.
5.8.5
Operation in sub-freezing conditions
When using the pump in sub-freezing conditions
where the pump is periodically idle, the pump should
be properly drained or protected with thermal devices
which will keep the liquid in the pump from freezing.
5.9 Stopping and shutdown
5.9.1
Shutdown considerations
When the pump is being shutdown, the procedure
should be the reverse of the start-up procedure.
First, slowly close the discharge valve, shutdown the
driver, then close the suction valve. Remember that
closing the suction valve while the pump is running is
a safety hazard and could seriously damage the
pump and other equipment.
5.9.2
Shutdown Guardian self-priming
At shutdown, the liquid in the discharge piping falls
back into the priming chamber and washes through
the impeller into the suction. The backflow creates a
siphon effect in the casing until the liquid level falls
below the bottom of the suction nozzle. The inertia of
the flow pulls fluid from the priming chamber to a
level lower than the initial priming fill. Though the
level is lower, there is still sufficient fluid in the
priming chamber to allow the pump to reprime itself.