Calculate required flow coefficient (Cv/Kv) for control valves handling liquids, gases or steam. Get valve size recommendation based on IEC 60534 standard.
Based on IEC 60534 / ISA-75.01. Always verify with valve manufacturer datasheet.
Cv is the flow coefficient of a control valve — it represents the volume of water in US gallons per minute that will flow through a fully open valve at a pressure drop of 1 psi. It is the universal measure of control valve capacity used by all valve manufacturers worldwide. The metric equivalent is Kv, representing flow in cubic metres per hour at 1 bar differential pressure.
This tool calculates the required Cv for liquid, gas and steam service using the IEC 60534-2-1 equations, and recommends a standard valve body size based on 75% valve opening at design conditions — the widely accepted engineering sizing criterion.
For non-flashing liquid flow: Cv = Q(gpm) / sqrt(dP(psi) / SG). Assumes turbulent flow and pressure drop below the critical cavitation pressure drop. For flashing or cavitating services, apply the FL correction factor per IEC 60534-2-1.
Separate equations apply for subcritical flow (dP less than P1/2) and critical choked flow (dP greater than or equal to P1/2). This tool automatically selects the correct equation. Flow rates are entered at normal conditions (0 deg C, 1.01325 bara).
Mass flow rate in kg/hr is used for steam sizing. Specific volume is estimated from inlet pressure. For critical letdown stations or desuperheating applications, obtain exact specific volume from steam tables at the actual inlet conditions.
Cv is the US imperial flow coefficient (GPM at 1 psi drop). Kv is the metric flow coefficient (m3/hr at 1 bar drop). The conversion is Kv = Cv x 0.8646. This tool calculates both simultaneously. European manufacturers typically quote Kv; US manufacturers use Cv.
Control valves sized to operate between 60 and 80% open at design flow retain controllability. A valve at 100% open has no control authority. A valve below 20% open operates in a non-linear region. The 75% criterion is a standard engineering rule of thumb for good rangeability.
This tool gives a reliable first estimate for preliminary engineering. For final selection, the valve vendor should perform detailed sizing using their software, accounting for installed gain, noise, cavitation and erosion considerations specific to their valve design.
Sizing equations per IEC 60534-2-1 — Industrial-process control valves: Flow capacity sizing equations for fluid flow under installed conditions, and ISA-75.01.01 — Flow Equations for Sizing Control Valves. These are the internationally recognised standards used by all major control valve manufacturers.