"The PSF109S model is great choice for controlling a vacuum pump. Controlling to a set point of -500 mBar ± 10% is no problem. If the switch is intended to shut off the vacuum pump at -500 mBar on increasing vacuum, the switch would typically reset at approximately -400mBar. In other words you can approximately -100mBar hysteresis between actuation and deactuation (negative) pressure. We can adjust the set point on increasing vacuum or deacreasing vacuum at no charge. This vacuum switch can be adjustable by the end-user as well. For proper electrical hook-up please follow our diagram since normally closed and normally open logic is reversed than what is shown on the Honeywell snap action switch."
In pratica:
Il valore regolabile io lo farei arrivare già tarato a -0,5 Bar, poi chi vuole può variarlo a piacere.
Il contatto chiude a -0,5 e riapre a -0,4 che secondo me è ottimo perchè mantiene abbastanza costante il vuoto, senza però essere troppo sensibile.
Per ulteriori info.. son qui.

Ricapitoliamo, chi ne vuole uno?