by Alexey Turceaninov
Ordering the wrong actuator is one of those mistakes that seems small until it isn't. An undersized unit burns out under load. An oversized one costs more than it should and may not even fit the valve. And a unit with the wrong voltage or enclosure rating means a return, a delay, and a conversation nobody wants to have.
The good news: knowing how to size an electric actuator is not complicated once you know the four or five key inputs. This guide walks you through each one in plain language — no engineering degree required.
Step 1: Know Your Valve Type and Motion
The first thing to establish is what kind of valve you're automating and what kind of motion it requires.
Quarter-turn valves (ball valves, butterfly valves, plug valves) rotate 90° between fully open and fully closed. These require a quarter-turn actuator — iVact's iVQ and iVS ranges cover this motion type.
Multi-turn valves (gate valves, globe valves, sluice gates) require multiple full rotations to travel from open to close. These require a multi-turn actuator — iVact's iVM range is designed for this.
Linear valves (certain globe valves, diaphragm valves, dampers requiring push/pull motion) need a linear actuator — iVact's iVL range handles this, with adjustable stroke ranges from 50 mm to 100 mm.
Getting this wrong means the actuator physically cannot operate the valve, so this is your first filter.
Step 2: Determine the Required Torque (or Thrust)
This is the most critical sizing parameter, and the most common source of errors.
For rotary (quarter-turn and multi-turn) valves:
You need to know the breakaway torque — the force required to unseat and begin moving the valve from its closed position. This is always the highest torque demand in the cycle, and it's what you size against.
How to get this number:
- Check the valve manufacturer's datasheet. Most reputable valve manufacturers publish torque requirements at rated pressure differential.
- If you can't find it, contact your valve supplier directly and ask for the "required actuator torque at maximum differential pressure."
- As a general rule, apply a safety factor of 1.25 to 1.5x on top of the published valve torque. This accounts for wear over time, sticky media, and worst-case pressure conditions.
Example: A butterfly valve that requires 200 N•m to operate should be paired with an actuator rated for at least 250–300 N•m.
The iVact iVQ range covers quarter-turn output torques from 6 N•m to 4,500 N•m, making it suitable for everything from small 1" ball valves up to large industrial butterfly valves.
For linear valves:
You need the required thrust (push or pull force) rather than torque. The iVact iVL range covers output thrusts from 250 KgF (550 LbsF) to 2,000 KgF (4,410 LbsF), with adjustable strokes from 50 mm to 100 mm.
Step 3: Confirm Your Power Supply
Electric actuators require a power supply to operate — and matching this correctly is non-negotiable. Connecting the wrong voltage to an actuator will at best trip a breaker and at worst destroy the unit.
The most common supply voltages are:
- 120V AC / 60 Hz — Standard North American single-phase supply, common in commercial and light industrial applications
- 240V AC / 60 Hz — Single-phase, common in larger commercial applications
- 480V AC / 60 Hz — Three-phase, typical in heavy industrial environments
- 24V DC — Common in instrumentation and control panel applications
- 24V AC — Less common, but used in some HVAC and building automation systems
What to do: Check the panel or junction box nearest to the valve location. Confirm the available supply voltage before specifying. If you're unsure, loop in your controls or electrical team — this is a one-minute conversation that saves a lot of pain.
Step 4: Define the Control Type
How will the actuator be commanded to move? There are three main options:
On/Off (Two-Position)
The actuator drives fully open or fully closed on a command signal. This is the simplest and most common configuration, used wherever you don't need intermediate positioning — isolation valves, shutoff valves, automated on/off process valves.
Modulating Control
The actuator can stop at any position between open and closed, controlled by an analog signal — typically a 4–20 mA input from a PLC or DCS. Essential for flow throttling applications where precise regulation is required. Requires an actuator with a positioner and position feedback output.
Three-Position (Open / Stop / Close)
A middle ground — the actuator responds to discrete open, stop, and close commands. Common in manual remote control applications and where a simple pushbutton panel is the interface.
For procurement purposes: if the word "modulating" appears anywhere in your process requirements or P&ID, you need to confirm the actuator is specified for modulating service. Not all actuators in a given range support modulating control at all voltages — verify this in the datasheet.
Step 5: Choose the Right Enclosure Rating
This is the one that procurement managers most often overlook until installation day. The enclosure rating tells you what environments the actuator can safely operate in.
The two rating systems you'll encounter are NEMA (North American) and IP (International). They're not identical, but here's a practical translation for common ratings:
| Rating | What it means in plain language |
|---|---|
| NEMA 4 / IP65 | Protected against dust and water jets from any direction. Suitable for outdoor, washdown, and general industrial use. |
| NEMA 4X / IP66 | Same as above, plus corrosion-resistant. Required in coastal, chemical, or food & beverage environments. |
| IP67 | Submersible to 1 metre for 30 minutes. iVact iVQ and iVS standard rating. |
| IP68 | Submersible to 8 metres for 120 hours. iVact iVM standard rating. Appropriate for underground vaults and flooded applications. |
| NEMA 7 / Class I Div 1 | Explosion-proof. Required in areas with flammable gases or vapors — oil & gas, chemical processing, certain mining operations. |
What to do: Identify the area classification and environmental conditions at the valve location before specifying. If the valve is outdoors in Canada, minimum IP67 is a good default. If it's in a classified hazardous area, you need explosion-proof certification — don't compromise on this.
Step 6: Consider Fail-Safe Requirements
If your process requires the valve to move to a defined safe position on power loss — fully closed to stop flow, or fully open for pressure relief — you need a fail-safe actuator.
There are two approaches:
Spring return — A mechanical spring set drives the valve to its fail position on power loss. No battery required. Fast response. The iVact iVS range is built for exactly this application, with spring return for fail-closed or fail-open configurations.
Battery backup — A battery maintains the actuator's ability to complete its last commanded position or drive to fail-safe on power loss. More flexible than spring return in some configurations.
If your P&ID or process safety documentation specifies "FC" (fail closed) or "FO" (fail open) on a valve, a standard on/off actuator is not sufficient — you need to spec for fail-safe.
Quick Sizing Checklist
Before submitting any actuator purchase request or RFQ, confirm you have answers to all of the following:
- Valve type (ball, butterfly, gate, globe, etc.)
- Required motion (quarter-turn, multi-turn, linear)
- Required torque or thrust at maximum differential pressure, with safety factor applied
- Available power supply voltage and phase
- Control type required (on/off, modulating, three-position)
- Enclosure rating required for the installation environment
- Fail-safe requirement (none, fail-open, fail-closed)
- Any special certifications required (explosion-proof, CSA, ATEX)
When in Doubt, Ask
If any of these inputs are unclear — particularly valve torque requirements or area classification — it is always worth a phone call before placing an order. A misspecified actuator that ships and arrives on site wrong costs far more in time and project delay than the cost of the unit itself.
The iVact team is available to walk through specifications with procurement and operations staff directly. You don't need a completed datasheet to start the conversation — a valve tag number, a P&ID line, or even a photo of the existing installation is often enough to get started.
Contact iVact at 1-888-383-5585 or sales@iVact.com, or use the iVact Product Selector to start narrowing down the right unit for your application.
