Air Regulator
A regulator is used to step down air pressure to a lower set point. You can have multiple regulators located in various places on your coach, like the one that is located under your front steps, this one is to keep the step cover from being a guillotine. Foretravel also put a regulator in the front ride height circuit so that when we go into travel mode, the front end 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 regulator is typically set at 60-65 psi.
The most difficult part of changing the regulators is just getting the coach safely up high enough to access them. You can purchase a new regulator at Napa, Lowes or HD. Cleaning the old sealant off of the fittings can be a bit tedious, but not too bad. Using the proper sealant is a must, as is being careful to leave the first couple of threads free of it so as not to get it into the air lines.