Abstract: A primary housing carries an air/oil separation element. A valve member extends into a throat of the element. A secondary housing forms a regulator chamber and an atmospheric chamber. A partition of the secondary housing delimits and fluidly seals the atmospheric chamber from the regulator chamber. The partition is moveable in opposite axial directions responsive to a change in a pressure differential between the atmospheric chamber and regulator chamber without the use of a spring. The valve opens into and is in fluid connection with the regulator chamber. The secondary housing is carried by the primary housing. Alternatively, a fluid port can open up out of the secondary housing and the valve not open into the regulator chamber.