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If during Purge Mode the vacuum level drops
to the minimum vacuum switch setting while
the pump is still running and before the purge
timer expires, the vacuum pump will come out
of purge and begin to pull vacuum on the system
once again. If the vacuum pump runs in Purge
Mode for the entire purge time setting, it will
stop running.
Example: Pump 1 starts as lead, vacuum
continues to fall, so Pump 2 starts. Vacuum
continues to fall, so Pump 3 starts. With 3
pumps running, the system is able to reach the
maximum vacuum switch setting and therefore
Pump 3 switches to Purge Mode and shuts down
after satisfying the Purge Timer. Pump 2 then
switches to Purge Mode. While Pump 2 is still in
Purge Mode, vacuum falls below the set value,
so Pump 2 comes out of Purge Mode to pull
vacuum once again.
4B.2 Automatic Purge
The system inlet piping contains an automatic
purge at each pump consisting of an electric
actuator isolation valve at the pump inlet and a
purge solenoid valve. The purge system is used
to reduce the effect of corrosive process gas.
While the pump is running to meet demand,
the inlet electric actuator isolation valve is open
and the purge solenoid valve is closed. Once the
demand is met, inlet valve closes and the purge
solenoid valve opens (Purge Mode).
The length of time of the purge cycle is adjustable
between 1 and 15 minutes with factory setting at
7 minutes. See Figure 4B.3 for the potentiometer
settings. If the pump purges for the amount of
time set for purge time, it will stop running. If
the pump has not stopped purging and the
vacuum level drops to where a pump is needed,
the pump will come back out of purge and start
running again. In either case, the inlet valve will
open, and the purge solenoid valve will close.
Lubricated Rotary Vane Laboratory Vacuum Systems
4B-3
The manual adjustable purge valve on the inlet
side of the purge solenoid valve is used to set the
rate of air that passes through the purge system
during a purge cycle. Set the manual adjustable
purge valve to a point where the pump achieves
a vacuum level of approximately 20" Hg or more
on the gauge located at the pump inlet during
the purge cycle.
If a pump selector switch is in the "AUTOMATIC"
position and the pump IS running (purging or
not) placing the selector switch in "PURGE/OFF"
will initiate a purge cycle and the pump will purge
for the purge time setting.
4B.3 Tank Drains
The standard tank drain consists of a manually
operated ball valve.
To drain the liquid from the tank, open the tank
bypass valve and close the tank isolation valves.
Then open the vent and drain valves. When
draining is complete, close the vent and drain
valves first, then open the tank isolation valves
and close the tank bypass valve.
4B.4 Emergency Shutdown/Alarms
The following conditions may arise during
operation.
4B.4.1 Pump / System Shutdown
To shut down an individual pump, place the
H-P/O-A switch for that pump in the "PURGE/
OFF" position. The inlet electric actuator isolation
valve associated with that pump closes, the inlet
purge solenoid valve opens, and each vacuum
pump runs until its purge time (based on control
panel settings) is completed. The purge cycle is
necessary to purge the pump of contaminants
before shutdown.
For an emergency, the entire system may be
shut down by pressing the "EMERGENCY STOP"
4107 9021 88.01
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