A pressure regulator for controlling flow of a fluid therethrough is provided. An upper housing member and a primary diaphragm define an upper chamber and a lower housing member and the primary diaphragm define a lower chamber. The pressure regulator further includes: a valve assembly provided within the upper chamber for controlling the flow of the fluid from an inlet body into the upper chamber; a secondary diaphragm provided within the lower chamber and defining a secondary diaphragm driving chamber; and a passageway connecting the inlet body and the secondary diaphragm driving chamber. During operation, the secondary diaphragm driving chamber is filled with the fluid at the inlet pressure, thereby subjecting the secondary diaphragm to the inlet pressure and generating the force for actuating the valve's disengagement from the inlet body. The pressure regulator functions to maintain the outlet pressure at a value that is a predetermined fraction of the inlet pressure.