Vmax - Vacuum Switch - How to Adjust

Issue: How to adjust the vacuum switch on a Vmax liquid ring vacuum pump system

Vacuum switches are used to automatically switch the vacuum pump on and off based on demand. On multiplex systems, the switches are labeled “Lead” or “Lag” and are marked with the corresponding Pump On and Pump Off setpoints. They are factory preset for your application and it is not recommended to adjust the vacuum switch. In the event it requires change, adjustments will be made using the two adjustment screws.



To increase the point at which the vacuum pump turns on, turn the range adjustment screw (R) counterclockwise. See the range scale on the switch for approximation. For vacuum use, set to the HgV scale, not the Psi scale. Use the vacuum gauge to observe the actual Pump On and Pump Off points.

To increase the differential (the difference between the Pump On and Pump Off points), turn the differential adjustment screw (D) counterclockwise. To obtain the correct Pump Off point, observe the physical opening of the contact switch as compared to the vacuum gauge reading.

The vacuum pump will not stop running because all systems are equipped with a 10-minute minimum run timer. These timers are to prevent the system from experiencing frequent start/stops. Remember to vary the vacuum level in the receiver or manifold to see a change in the vacuum level when adjusting the switches.


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