Cla-Val Models 250-01 and 605-01 Differential Pressure Relief Valves are hydraulically operated, pilot-controlled, modulating valves. They are designed to maintain a constant pressure differential between any two pressure points in a system where the closing of the valve directly causes the differential pressure to increase. The valves tend to open on an increase in differential pressure and close on a decrease in differential pressure. Typical applications include differential pressure control in centrifugal pumping systems and chilled water circulating loop systems.