How to Calculate Required Torque for Valve Actuation

How to Calculate Required Torque for Valve Actuation

When automating a valve with an electric actuator, one of the most important specifications to consider is torque — the rotational force required to open or close the valve. Unlike pneumatic actuators, which rely on compressed air pressure (typically between 60–100 psi), electric actuators depend on motor power and gear reduction to generate torque.

Getting the torque right ensures smooth operation, avoids mechanical damage, and extends the life of both the actuator and valve.

Why Torque Calculation Matters

Torque is what allows the actuator to overcome:

• Friction in the valve stem and seals
• Backpressure from the media (liquid or gas) inside the pipe
• Seating resistance when closing the valve
• Environmental factors like corrosion or debris buildup

If the actuator doesn’t produce enough torque, it may stall, overheat, or fail to fully open/close the valve. If it produces too much, it can damage the valve internals or cause premature wear.

Step-by-Step Guide to Calculating Required Torque

1. Get the Valve Manufacturer’s Torque Specifications

The most accurate way to determine how much torque you need is to consult the valve manufacturer’s data sheet. Most reputable valve manufacturers provide:

Torque Type	Description
Breakaway Torque	The torque needed to start moving the valve from a stationary position
Running Torque	The torque needed to keep the valve moving once it's in motion
Seating Torque	The torque needed to fully close the valve and ensure a tight seal

Important: Use the highest torque value (usually breakaway torque) as your base for actuator selection.

2. Add a Safety Margin (20–30%)

Even if you have exact torque values, it’s wise to add a safety margin of 20–30% to account for:

• Unexpected pressure spikes
• Friction increase due to wear or debris
• Temperature variations affecting seals
• Valve aging over time

Example:

If the valve’s breakaway torque is 200 Nm, you should select an actuator rated for at least:

200 Nm × 1.25 = 250 Nm

This ensures reliable operation across the valve’s lifecycle.

3. Consider Environmental and System Factors

Some real-world conditions can increase torque demand:

Factor	Effect on Torque
High backpressure	Increases breakaway and seating torque
Corrosive environments	Can stiffen valve stem or seals
Frequent cycling	Increases wear and torque demand over time
Extreme temperatures	Can stiffen lubricants or expand materials
Pipe strain or misalignment	Adds mechanical resistance

If any of these apply, consider increasing your safety margin beyond 30%.

4. Match the Actuator to the Torque Requirement

Once you’ve calculated the required torque, choose an actuator that meets or exceeds that value. Also, ensure:

• It operates within your system’s voltage supply
• It supports your control signal (e.g., 4–20 mA, Modbus, on/off)
• It fits within your space and mounting constraints
• It has the appropriate IP rating for your environment (e.g., IP67 for outdoor or washdown areas)

Example: Calculating Torque for a 4” Ball Valve

Let’s walk through a real-world example:

• Valve Type: 4” ball valve
• Breakaway Torque (from valve specs): 200 Nm
• Running Torque: 150 Nm
• Seating Torque: 180 Nm

Step 1: Use the Highest Torque Value

200 Nm (breakaway torque)

Step 2: Add a 25% Safety Margin

200 Nm × 1.25 = 250 Nm

Step 3: Select an Actuator

Choose an actuator rated for at least 250 Nm. If the system operates in a harsh environment, go for 300 Nm to be safe.

Common Mistakes to Avoid

Electric actuators are essential components in industrial automation, offering precision, energy efficiency, and reliable control of valves, dampers, and other mechanical systems. However, even experienced engineers and procurement professionals can make mistakes when selecting, installing, or maintaining them.

Based on real-world applications and insights from the Valen Tech article on pneumatic actuators, here are the most common mistakes to avoid when working with electric actuators — and how to prevent them.

1. Underestimating Torque Requirements

The Mistake:

Assuming a generic torque value or guessing based on valve size instead of consulting the valve manufacturer’s specifications.

Why It’s a Problem:

• An undersized actuator may stall, overheat, or fail to move the valve under real-world conditions.
• Torque needs vary depending on breakaway torque, seating torque, and running torque — not just valve size.

How to Avoid It:

• Always get the exact torque values from the valve data sheet.
• Use the highest torque value (usually breakaway torque) as your base.
• Add a 20–30% safety margin to account for wear, pressure changes, and friction.

2. Ignoring the Safety Margin

The Mistake:

Selecting an actuator with exactly the required torque, without allowing for real-world variations.

Why It’s a Problem:

• Over time, valves may become stiffer due to corrosion, debris, or seal wear.
• Unexpected pressure spikes or temperature changes can increase torque demand.

How to Avoid It:

• Always oversize the actuator slightly — for example, if a valve needs 200 Nm, choose an actuator rated for 250–300 Nm.
• This ensures long-term reliability and reduces the risk of failure.

3. Mismatching Control Signals

The Mistake:

Choosing an actuator with a control signal that doesn’t match the control system (e.g., using a 4–20 mA input actuator with a Modbus PLC).

Why It’s a Problem:

• The actuator may not respond correctly to control commands.
• This leads to poor positioning, inconsistent control, or even system downtime.

How to Avoid It:

• Ensure the actuator supports your system’s control protocol:
  • 4–20 mA
  • 0–10 VDC
  • Modbus RTU
  • Digital On/Off
• For digital systems, confirm compatibility with PROFINET, Ethernet/IP, or CANopen as needed.

4. Overlooking Environmental Conditions

The Mistake:

Choosing an actuator without considering environmental factors like temperature, moisture, or corrosion.

Why It’s a Problem:

• Extreme temperatures can affect motor performance and lubrication.
• Moisture or dust can damage internal electronics or gears.
• Corrosive environments can reduce actuator lifespan or cause premature failure.

How to Avoid It:

• Choose an actuator with the appropriate IP rating:
  • IP65: Dust and water-resistant
  • IP67: Submersible in water up to 1 meter
  • IP69K: Resistant to high-pressure washdowns
• Use corrosion-resistant materials (e.g., stainless steel housing) in harsh environments.

5. Using an Oversized Actuator

The Mistake:

Choosing an actuator with excessive torque to “play it safe.”

Why It’s a Problem:

• Too much torque can damage the valve stem, over-tighten the seal, or cause internal wear.
• Oversized actuators are heavier, more expensive, and may not fit in tight spaces.

How to Avoid It:

• Stick to the valve manufacturer’s specs and recommended safety margin.
• Match the actuator’s torque to the valve’s maximum required torque, not the actuator’s upper limit.

6. Neglecting Power Supply Compatibility

The Mistake:

Selecting an actuator with a voltage or current rating that doesn’t match the available power supply.

Why It’s a Problem:

• Low voltage can reduce torque and cause overheating.
• High voltage can damage the actuator’s motor or electronics.

How to Avoid It:

• Ensure the actuator operates within your system’s voltage range:
  • 24 VDC
  • 120 VAC
  • 230 VAC
• Use a stable power supply and include overcurrent protection.

7. Forgetting About Feedback and Position Control

The Mistake:

Using an actuator without position feedback in applications requiring precise modulation.

Why It’s a Problem:

• Without feedback, you can’t verify the actuator’s position.
• This leads to poor control in modulating applications like process control loops.

How to Avoid It:

• Choose actuators with integrated encoders or potentiometers for precise position control.
• Use closed-loop control systems for high-accuracy applications.

8. Assuming Electric Actuators Always Replace Pneumatic Ones

The Mistake:

Thinking electric actuators are always better than pneumatic ones.

Why It’s a Problem:

• Pneumatic actuators have their own advantages — especially in hazardous environments or where fast response is needed.
• They operate on 3–15 psi control signals and typically use 60–100 psi power air — which is simple and safe in explosive atmospheres.

How to Avoid It:

• Evaluate both types based on:
  • Precision needs
  • Control system compatibility
  • Power availability
  • Safety requirements
• Don’t assume one is always better — choose based on the application.

9. Ignoring Installation and Mounting Requirements

The Mistake:

Installing the actuator without checking mounting dimensions, orientation, or mechanical alignment.

Why It’s a Problem:

• Misalignment can cause binding, extra torque demand, or mechanical stress.
• Some actuators are sensitive to mounting orientation, especially those with internal cooling or lubrication.

How to Avoid It:

• Follow the manufacturer’s installation instructions.
• Ensure mechanical compatibility with the valve or damper.
• Check mounting brackets, couplings, and alignment before powering the actuator.

Avoiding these common mistakes can save time, reduce maintenance costs, and ensure smooth, long-lasting operation of your automation system. Whether you're upgrading from a pneumatic actuator (which operates between 60–100 psi) or designing a new electric actuator system, attention to detail in torque, control, environment, and installation makes all the difference.

Need Help Choosing the Right Electric Actuator?

At Valen Tech Co., Ltd., we specialize in delivering high-performance electric actuators designed for industrial durability and precision. Whether you need a compact actuator for light-duty valves or a high-torque model for large butterfly valves, Valen Tech has the right solution for your automation needs.
Contact us for custom solutions

Let us help you make the right choice — where torque meets performance.