Pressure Drop from Kv

The pressure drop across a valve at a given flow rate is calculated as: ΔP = SG × (Q ÷ Kv)², where ΔP is the pressure drop in bar, Q is the flow rate in m³/h, Kv is the valve flow coefficient, and SG is the specific gravity of the fluid. Pressure drop increases with the square of the flow rate, so a valve passing twice the flow experiences four times the pressure drop. This square-law relationship is important when accounting for valve losses in pump head calculations. The total pump head for a hydronic system must include the pressure drops across all valves, fittings, coils, and straight pipe at the design flow rate. Undersizing a control valve creates excessive pressure drop that wastes pump energy, while oversizing reduces valve authority and makes flow control less stable. A well-sized valve typically accounts for 25–50% of the total branch circuit pressure drop.