Abstract: The pressure regulator has a regulator body with a control chamber and outlet and inlet passageways opening thereto, a bonnet with a bonnet chamber and a diaphragm separating the chambers. A filter housing is mounted in the control chamber and mounts a filter and a valve seat that opens to the inlet passageway while spring urged mechanism moves the a valve stem to permit fluid flow through the valve seat and into the control chamber between the filter and diaphragm when the pressure therein falls below a preselected level, and then through the filter to the outlet passageway. When the pressure in the outlet passageway is at or above a preselected value, the pressure acts against a diaphragm whereby the piston retains the valve stem in a fluid flow blocking position.