Differential Pressure Regulators; Sliding Gate Seat; 1/4″ – 2″ (DN8 – DN50); The Mark 63 - differential pressure regulator is designed to maintain a constant differential between the pressure on the discharge side of the regulator and the signal pressure loaded on the diaphragm. The Mark 64 provides the same flow capacity but with less offset in controlled pressure due to a larger diaphragm. This differential pressure regulator valve series is ideal in fuel oil atomization applications. A negative differential version is also available.