# Calculation Methods - Valves (3 Port)

The pressure loss across a valve is a function of flow. In FluidFlow this loss relationship can be expressed as either: K, Kv/Cv, or Kf. The pressure loss coefficient, K is defined by the equation: K = 2 ΔP / (ρv2) The pressure loss coefficient expressed as equivalent length in terms of pipe diameters, Kf is defined by the equation: Kf = 2 ΔP / (ρfTv2) where fT is the fully turbulent flow friction factor which is simply a function of size. This definition is used almost exclusively by Crane [13]. The valve flow coefficient, Kv or Cv is expressed by the equation: Kv = C1 Q (ρ/ΔP)0.5 where C1 is a constant that depends upon the units used. For a 3 way valve it is not possible to enter data regarding pressure loss and flow other than for the fully open position.