the system reaches its normal operating vacuum
and the lag pump times out and stops.
When the vacuum level increases to the
maximum vacuum set point, the last pump
to come on will go into Purge Mode (First On/
Last O
ff
). If the pumps don’t satisfy the vacuum
setting, they will continue to run for as long as
the pump alternation time is set. Once the pump
alternation time is reached, the lead pump will
go into Purge Mode regardless of the current
vacuum level.
If during Purge Mode the vacuum level falls to the
fi
rst virtual pressure switch again, the vacuum
pump will come out of purge and begin to pull
vacuum on the system 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 virtual
pressure switch level, so Pump 2 comes out of
Purge Mode to pull vacuum once again.
4A.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 e
ff
ect 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 5 and 15 minutes with factory setting
at 7 minutes (see Appendix A for more details).
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.
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.
4A.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
fi
rst, then open the tank isolation valves
and close the tank bypass valve.
Figure 4A.1 Main Screen - Reset Button
(DOL shown with Lag Alarm Enabled)
Lubricated Rotary Vane Laboratory Vacuum Systems
4107 9021 88.01
4A-2
