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5. Vacuum Control System
To gain a better understanding of how a Quincy Vacuum Pump operates, let’s assume the Quincy vacuum pump is
set to operate from 20” to 23” Hg vacuum, with a lower set point of 20” Hg and an upper set point of 23”Hg
differential.
When the start button on the vacuum pump is activated, two operations occur. First, electric power is routed through
normally closed contacts on the vacuum switch to the normally open solenoid valve causing it to shift closed.
Second, the inlet valve permits air to flow from the vacuum system to the vacuum pump inlet where it is compressed
to atmospheric pressure and discharged through the air/lubricant reservoir.
The control system remains in this state until the vacuum level in the plant system increases to 20” Hg. At this point,
the vacuum regulator permits more vacuum to be applied to the inlet valve air cylinder causing it to gradually close
the inlet valve until the amount of air permitted into the vacuum pump is equal to the amount of air being leaked into
the plant vacuum system through use. If vacuum usage continues to decrease causing the level to increase to 23”
Hg, the vacuum switch trips, opening the normally closed contacts and stopping power flow to the solenoid. This
causes the solenoid to shift to the normally open position.
This action allows enough air flow from the inlet valve air cylinder through the solenoid to the vacuum pump inlet to
close the inlet valve completely and allows the vacuum level in the system from rising above the maximum set point
of 23”Hg. This cycle continues as required by the system usage and the vacuum level is maintained between 20”Hg.
to 23”Hg. If the vacuum pump stops during operation, either manually by pressing the stop button or automatically
due to a high temperature condition, a check valve feature in the inlet valve prevents air from entering the system
through the vacuum pump.
Do not operate the pump continuously at inlet vacuum levels of 0 – 10” HgV as excessive fluid carryover can occur.
Consult the factory if operating within 0 – 10” HgV.
6. Auto Dual with Modulation
The Auto/Dual system offers two choices of controlling the Quincy QSVB Vacuum pump. With the selector switch
in the “Continuous Run” position, the vacuum pump operates continuously matching demand with a differential pilot
valve controlling the position of the inlet valve. When maximum system vacuum is reached, the vacuum switch
opens, closing the inlet valve and, although the vacuum pump continues to run, no more vacuum will be produced.
When the Auto Dual mode is selected, the vacuum pump will also perform as above; however, a solid state timer is
activated when the vacuum switch contacts open. This timer is adjustable within a ten (10) minute range. When the
timer reaches the end of its delay, the vacuum pump will automatically shut down and assume a "stand-by" mode.
Upon a drop in vacuum pressure, the vacuum switch contacts close, restarting the vacuum pump automatically. The
timer should be set, during unit start-up, for a minimum of ten (10) minutes.
During the unloaded/timing mode, if plant pressure should drop causing the vacuum switch contacts to close, the
vacuum pump will continue to operate, resetting the timer and instructing the inlet valve to re-open.
When operation in the Auto mode allows the vacuum pump to start and stop more than five (5) time per hour, select
the Continuous Run mode and allow the unit to operate continuously. Excessive motor starts will shorten motor life.
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