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SECTION VII
SERVICE ADJUSTMENTS
! WARNING
Read all safety cautions and warnings in Section I prior to attempting any service.
1. Differential Pilot Valve
By manual regulation, slowly close the valve, allowing the system pressure to reach the desired vacuum level. Adjust
the screw on the bottom of the differential pilot valve so that a slight stream of air can be felt coming from the orifice
adjacent to the adjustment screw.
When this air is felt, air is beginning to pass through the pilot valve, causing the valve to modulate toward its closed
position, thereby, reducing the volume of air being compressed.
To raise pressure turn the adjusting screw in (clockwise), to lower pressure turn screw out (counter clockwise).
Maximum vacuum under modulation is 29.6” HgV. for the QSVB vacuum pumps.
2. Vacuum Pressure Switch
The vacuum pressure switch determines at what pressure the vacuum pump will load and unload. Standard factory
settings are listed in the QSVB Specifications. Never exceed these pressures. If a lower setting is desired, adjust the
differential pilot valve first and set the pressure switch cut-out point to no more than 2” HgV differential. The
adjustment is made by turning the wheel clockwise to increase the cut-in/cut-out pressure and counter-clockwise to
lower the cut-in/cut-out pressure. The pressure switch should unload the vacuum pump by the time it reaches the
20% load point. Consult your parts book for proper sheave and belt part numbers.
3. Water Regulating Valve (water-cooled units only)
The water regulating valve senses fluid temperature and opens or closes, regulating water flow from the unit. It is
factory set to maintain 190°F air discharge temperature. Due to different incoming water temperatures and/or
pressures at the customer location, valve adjustment should be checked during start-up to maintain 190°F discharge
temperature. To increase fluid temperature, decrease water flow by turning the adjustment screw clockwise. To
decrease fluid temperature, increase water flow by turning the adjustment screw counter clockwise.
Water pressure
should be 40 PSI minimum/100 PSI maximum. Water temperature should be 50°F minimum/90°F maximum.
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