A globe valve regulates flow by moving a plug or disc toward or away from a seat. The body directs fluid through that controlled opening. This calculator estimates the required Cv for a simplified turbulent-liquid case and compares it with an entered rated Cv. The animation shows stem movement separately; the result does not determine valve position.
Globe Valve Interactive Calculator
Calculate a simplified required liquid Cv, compare it with an entered rated Cv, and view the globe-valve flow path.
Equation Used
- Incompressible turbulent liquid and US Cv convention with Q in US gpm and pressure drop in psi.
- Entered pressure drop is the applicable valve sizing pressure drop and entered specific gravity applies at the operating condition.
- Entered rated Cv is independently obtained for the identified valve/trim; utilization does not equal travel percentage.
- No viscosity, reducers, choking, cavitation, flashing, noise, actuator, force, leakage or safety model.
Simplified turbulent-liquid capacity comparison only. Rated-Cv utilization is not valve opening. Exact position requires the identified valve's manufacturer Cv-versus-travel curve. No choking, cavitation, flashing, viscosity, piping correction, noise, actuator or safety model is included.
How a globe valve controls flow
The stem moves the plug relative to the seat. Closing the plug restricts the passage; lifting it increases the available flow area. Globe valves can have different body arrangements and trim profiles, so they do not all share one relationship between travel and flow.
A threaded handwheel may move the stem manually. A control valve may instead use a pneumatic or electric actuator, often with a positioner. Body pressure, plug area, packing friction and shutoff requirements affect actuator selection; they are not calculated here.
Main parts
- Body and bonnet: contain the fluid and support the internal parts.
- Plug and seat: form the adjustable restriction and shutoff interface.
- Stem: transmits motion to the plug.
- Packing: seals around the moving stem.
- Handwheel or actuator: supplies the operating motion and force.
Where globe valves are used
Globe-style valves are used for flow regulation in water, steam and process-fluid systems. The appropriate materials, pressure class, trim and actuator depend on the service. The calculator on this page applies only to the stated liquid-flow approximation; it cannot size a steam or gas valve.
Control-valve selection also considers the required flow range and installed system behavior. A large rated Cv alone does not establish good control, acceptable noise or suitability for a fluid.
Simplified liquid Cv comparison
For the basic US-unit turbulent-liquid case, required Cv=Q sqrt(SG/delta P), where Q is US gpm, SG is liquid specific gravity and delta P is psi across the valve. Rated-Cv utilization is 100 times required Cv divided by the entered rated Cv.
That percentage is not valve opening. The relation between travel and Cv depends on the exact body, trim and inherent flow characteristic. Emerson's full procedure also checks piping factors and the limiting pressure drop for choking.
Example: a liquid capacity comparison
Enter 100 US gpm, a pressure drop of 10 psi, specific gravity 1 and rated Cv 150. Assume the liquid is incompressible and turbulent, and that choking and piping corrections do not apply.
- Required Cv = 100 × √(1/10) = 31.62.
- Rated-Cv utilization = 100 × 31.62 / 150 = 21.08%.
- Cv margin = 100 − 21.08 = 78.92%.
- Hydraulic power loss = 100 × 10 / 1714 = 0.583 hp.
The 21.08% result is a capacity ratio, not 21.08% stem travel. The power result is fluid power dissipated across the pressure drop, not actuator power. Manufacturer data and the full service conditions are still needed to select a valve.
Completing a valve selection
The simplified comparison can screen an entered operating point, but final selection requires the exact manufacturer's sizing data and Cv-versus-travel curve plus upstream pressure, downstream pressure, temperature, vapor pressure, critical pressure, viscosity, piping geometry, noise and cavitation checks. Actuator sizing and safe shutoff require additional force and service data.
Frequently asked questions
Does 50% rated-Cv utilization mean 50% open?
No. It means the required Cv is half the entered rated Cv. Position depends on the exact trim’s Cv-versus-travel characteristic and the installed system.
What does a negative Cv margin mean?
The required Cv exceeds the entered rated value under the simplified assumptions. A positive margin only passes this capacity comparison; it does not complete valve selection.
Can I use the liquid inputs for steam?
No. Steam and other compressible fluids need a different sizing procedure and additional fluid-state data.
Does the result check cavitation or choking?
No. Vapor pressure, critical pressure, recovery factors and relevant piping factors are not supplied. Use the manufacturer’s full sizing procedure.
Why does stem motion not match Rated Cv Used?
The animation demonstrates an opening-and-closing cycle. It has no valve-specific travel curve, so it does not convert the capacity ratio into stem position.
Is Loss Power the power needed by an actuator?
No. It is the rate at which hydraulic energy is dissipated across the entered pressure drop. Stem force, travel and actuator efficiency are separate requirements.
Manufacturer technical reference
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