A regulator is to step down the air pressure to a needed set point. You can have multiple regulators located in various places on your coach, like the one that is or on your air ride drivers chair or the one that is located under your front steps , this one is to keep the step cover from being a guillotine and also operates the outside step.
They put a regulator in the front brake circuit so that when we go into travel mode, the front end (which is lighter) doesn't raise faster than the rear and confuse us into thinking we're ready to travel before the rear is at travel height! That is set at 60 psi.
Husky Regulator w/Gauge
Model # HDA70900AV
Used to adjust air pressure from 0- 200 PSI. 1/4 In. NPT inlet and outlet.