1> Definition Flow coefficient KV (m³/h): The flow rate, in m³/h, of water at 5°C to 40°C passing through the valve when the pressure drop across the valve is 1 bar; this value is denoted as KV. Flow coefficient CV (gal/min): The flow rate, in gallons per minute, of water at 5°C to 38°C passing through the valve when the pressure drop across the valve is 1 psi (0.0689 bar); this value is denoted as the CV. II> Calculation of the Flow Coefficient CV(gal/min)=1.156×KV(m3/h) KV(m3/h)=0.865×CV(gal/min) 3> Valve Flow–Pressure Drop Calculation Formula
Pressure differential condition
Fluid
P out > 12 P Enter
P out ≤ 12 P entry
Common liquid
Viscosity ≤ 200 cSt
Q Liquid =3.158K V
Q Liquid =3.158kV
Gas
Q air =4786K V
Q air =2393kV
Saturated water vapor
Q car =229K V
Q car =114K V *P Enter
Symbolic Meaning Q液 (m³/h): Liquid flow rate Q汽 (kg/h): Steam flow rate KV (m³/h): Valve flow coefficient G_gas: Specific gravity of the gas (air = 1) G liquid: specific gravity of the liquid (water = 1) T(℃): fluid temperature P_in (MPa): Absolute pressure at the inlet (gauge pressure + atmospheric pressure) P_out (MPa): Absolute pressure at the outlet (gauge pressure + atmospheric pressure) Q gas (N m³/h): Gas flow rate under standard conditions (15°C, one standard atmosphere)
4> Flow Coefficient of Ball Valves and Recommended Maximum Water Flow Rate
Ball valve inner diameter
[mm]
KV value
Recommended water flow rate
Ball valve inner diameter
[mm]
KV value
Recommended water flow rate
Pressure ≤ 5 bar
Pressure ≥ 16 bar
Pressure ≤ 5 bar
Pressure ≥ 16 bar
5
1.2m3/h
≤0.3 m³/h
≤0.6 m³/h
25
36.6m3/h
≤9.2m3/h
≤18.3m3/h
7
2.6m3/h
≤0.7 m³/h
≤1.3 m³/h
32
62.9m3/h
≤15.7m3/h
≤31.4m3/h
10
5.3m3/h
≤1.3 m³/h
≤2.7 m³/h
40
103.2m3/h
≤25.8m3/h
≤51.6 m³/h
15
12.4m3/h
≤3.1 m³/h
≤6.2 m³/h
50
169.2m3/h
≤42.3 m³/h
≤84.6 m³/h
20
22.2m3/h
≤5.6 m³/h
≤11.1m3/h
65
285.6m3/h
≤71.4 m³/h
≤143.0 m³/h
5> Air flow data at 20°C for ball valves — pressure drop data
Ball valve nominal diameter
[mm]
Valve air flow rate, standard L/min (standard liters per minute)
P Enter 
P entry 
