Fluid control
Table 1. General torque relations according to valve types( ISA, 2020; Emerson, 2020; Chen et al., 2016) Valve Type Torque Relation Torque Increase Trend
Butterfly Valve T≈C ⋅ D 3 ⋅ ΔP Proportional to the cube of the diameter
Ball Valve T≈C ⋅ D 2 ⋅ ΔP Proportional to the square of the diameter
Globe Valve T≈C ⋅ D 2 ⋅ ΔP Proportional to the square of the diameter
Gate Valve T≈C ⋅ D 2 ⋅ ΔP Proportional to the square of the diameter
R valve
: Represents the effective radius( m) or moment arm from the point where the pressure force is applied to the axis of rotation. This varies according to the design of the valve.
τ friction
: The torque component( Nm) resulting from mechanical friction between the valve’ s bearings, gears or other moving parts. This value depends on the valve size, shaft diameter, bearing materials and lubrication. It is usually determined experimentally. τ seal
: The torque component( Nm) resulting from the friction force exerted by the sealing elements( seals) on the moving parts of the valve. The seal material( PTFE, NBR, metal, etc.), the design and tightness of the seal greatly affect this value. This is usually determined by experimental data.
While the equation above shows the main components that affect torque, there is no single universal equation that can provide accurate calculations for every valve type and size, for the following reasons: 1. Complex geometries: The internal geometries of valves( especially globe valves, butterfly valves) are very diverse and it is complex to accurately determine the effective surface area and moment arm on which pressure acts.
2. Coefficients of friction: Mechanical friction and seal friction depend on a large number of variables( material properties, surface roughness, temperature, pressure, lubrication status) and cannot be easily expressed with standard formulas.
3. Dynamic effects: Dynamic effects such as fluid velocity and turbulence can also play a role in torque, especially at high flow rates.
4. Manufacturer data: Valve manufacturers design their valves according to specific standards and perform extensive testing in their own laboratories to obtain the most accurate torque values. This data is the most reliable source for the end user to select the right actuator.
Torque relation according to valve diameter in butterfly valves
In butterfly valves, the torque requirement due to flow forces increases proportionally to the cube of the valve diameter. This means that the dynamic pressure and flow forces acting on the valve disc increase with the cube of the diameter.
T butterfly
: Torque( Nm) C: Experimental coefficient( between 0.01 and 0.03) D: Valve diameter( m) ΔP: Pressure difference( Pa)( Val-Matic, 2019)
Torque relation according to valve diameter in ball valves
Ball valves determine the torque requirement by the effect of seal friction and flow forces. Torque is generally proportional to the square of the valve diameter( Chen et al., 2016):
τ ball
: Torque( Nm) C: Experimental coefficient( between 0.05 and 0.2) D: Valve diameter( m) ΔP: Pressure difference( Pa) This formula provides a practical approach for initial engineering estimates and actuator pre-sizing( Emerson, 2020).
General trends by valve diameter for other valves
Globe valves: Torque requirement depends on sealing forces and shaft friction rather than flow forces. It is approximately proportional to the square of the diameter. Gate valves: Since they are mostly linear in motion, they are generally expressed as force( F); in rotary actuators, torque conversion is related to the square of the diameter. Plug valves: Similar to ball valves, torque increases approximately with the square of the valve diameter. Pinch valves: Torque requirement is generally independent of flow forces; it depends on the friction between the seal and the elastomer.
Summary of components in the torque equation
Additionally, general torque relationships according to valve type are summarised in the table below:
Evaluation in terms of energy efficiency
High torque requirements require a larger motor and drive mechanism for the actuator, increasing operating costs and energy consumption( ISA, 2020). To increase energy efficiency:
• Friction reducing coatings and seals should be used.
• Valves should be kept in low friction condition by regular maintenance and cleaning.
• The actuator should be selected according to the maximum torque requirement in the flow.
Conclusion
Valve torque is not a fixed value and varies depending on installation and flow conditions. In butterfly valves, the torque requirement is a cubic function of the valve diameter, while in globe and other valve types it is generally proportional to the square of the diameter. These relationships need to be considered in terms of actuator selection and system energy efficiency.
References available on request.
44 Valve World August 2025 www. valve-world. net