Extremely efficient, the DPCV is set to a maximum differential pressure which ensures flow cannot exceed a desired rate. return pipework the impulse tube from the flow pipework should be connected to P3. DPAF961 / DPAR961 DN15 to DN50. Dual valve structure TYNE DPCV is used for heating water systems (air conditioning) and has the following features: Maintains a constant system pressure. Hattersley's range of FutureFlow Differential Pressure Control Valves (DPCV) specifically aimed at optimising system performance.