In pneumatic actuator selection, the difficult part is not "which one to choose" but stating the operating conditions clearly. When the operating condition information is complete, selection can often be settled in ten minutes; when the operating conditions are vague, problems such as "not enough torque to drive it", "the interface will not fit" and "the valve stops in a position where it should not stop after air loss" easily arise.
The HES product line covers AT, GT, AW and A series pneumatic actuators, G series (hydraulic) pneumatic actuators, ST-series linear pneumatic actuators, and the full single-acting/double-acting range, and can match the vast majority of industrial valve operating conditions. This article provides a 6-step process for rapid selection according to operating conditions; just follow it.
1. Step One: Write the 5 Items of Operating Condition Information Clearly
Before selection, prepare the following five items; missing any one of them may lead to a wrong choice:
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Medium and temperature: medium type, working temperature range (which determines the choice of seal material and grease)
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Valve and diameter: valve type (ball valve, butterfly valve, gate valve, control valve), diameter, required operating torque
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Pressure and air supply: pipeline pressure rating, on-site air supply pressure (commonly 0.4-0.7MPa) and air supply quality
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Action and safety requirements: switching frequency, whether a return to the safe position after air loss is required, and whether it is used in a safety interlock loop
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Environmental conditions: indoor or outdoor, corrosion and dust, whether explosion protection is required, installation space limits
Do this step well and the rest of the choice is basically "matching to the right slot".
2. Step Two: First Determine the Mode of Action - Single-Acting or Double-Acting
The mode of action is determined by the required behavior after air loss, which is the least ambiguous step in selection:
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Automatic return to the safe position after air loss is required (emergency shut-off, safety interlock, unstable air supply) → choose single-acting (spring-return)
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Only switching action is needed with no fail-safe return requirement, or position holding has already been achieved by other means → double-acting can be chosen
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Greater output torque is required and the air supply pressure is limited → double-acting can make fuller use of the air supply force
If the torque required by the valve is relatively large and fail-safe is also mandatory, then a single-acting actuator should be chosen but with the size enlarged according to the torque requirement - determine safety first, then torque, and do not reverse the order.
3. Step Three: Then Determine the Series - Rotary, Linear or Hydraulic
Once the mode of action is decided, next determine the series according to the valve's form of motion and torque requirements:
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Rotary valves (ball valves, butterfly valves and other rotating valves): choose a rack-and-pinion rotary actuator; the AT, GT, AW and A series cover conventional diameters and torque ranges and have good interface versatility
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Linear valves (gate valves, globe valves and control valve plugs): choose the ST-series linear pneumatic actuator and select by the required thrust and stroke
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Extra-large diameter or extremely large torque is required: the G series (hydraulic) pneumatic actuator can be considered to obtain greater output torque within limited space
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Manual emergency operation is required: pair with a manual mechanism or hydraulic manual pump
4. Step Four: Calculate the Torque and Determine the Size - Don't Let the Actuator "Fail to Drive"
Torque calculation is the step where problems most easily arise; the key points are three sentences:
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Calculate according to the operating torque actually required by the valve, not by matching the actuator's rated value;
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Leave a safety factor: reserve margin during selection (generally 1.3 times or more is recommended) to handle the torque increase caused by medium scaling, differential pressure fluctuation and seal aging;
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Pay attention to calculating the force at the lower air pressure limit: the valve must still be driven when the air supply pressure fluctuates to the lower limit, so the calculation should take the lowest pressure that may occur on site.
In addition, verify whether the connecting interface complies with ISO 5211 and whether the accessory mounting face complies with the NAMUR standard - once the interfaces are right, the actuator, valve and accessories can be installed and used immediately.
5. Step Five: Complete the Accessories and Interfaces - Go Through Them Once More Before Selection
Once the actuator body is decided, the accessory configuration must likewise be determined at the selection stage to avoid changing interfaces after delivery:
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Solenoid valve: pair single-acting with single-solenoid control and double-acting with double-solenoid control; note whether the air supply bore and flow rate match the action speed requirement
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Valve positioner: needed for regulating operating conditions, receiving a 4-20mA signal to achieve precise control
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Limit switch: configured when a switch position feedback signal is required; note the installation position and the adjustable range of the cams
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Filter regulator (FRL unit): an item that guarantees air supply quality and is recommended as mandatory
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Manual mechanism: an essential item when manual operation is needed during a power failure or air loss
6. Step Six: Verify Delivery and Common Misconceptions
Checklist: whether the model and specifications are consistent with the operating conditions, whether the mode of action meets the safety requirements, whether the torque margin is sufficient, whether interfaces and accessories are complete, and whether the nameplate and accompanying documents are complete; after delivery, first perform a full-stroke action test and, if necessary, hold at rated pressure for a leak test (pressure drop not more than 5kPa in 5 minutes).
Common misconceptions:
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Reporting only the diameter and not the torque - the torque differs greatly among different valves and media of the same diameter
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Looking only at the rated torque and not the torque at the lowest air pressure - the problem only surfaces when the air supply pressure drops
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Omitting the positioner in regulating operating conditions - the insufficient control accuracy is only discovered after commissioning
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Ignoring accessory interface standards, which results in the actuator failing to fit the valve and positioner or requiring a modified bracket
Recap of key points: to select an HES pneumatic actuator by operating conditions, follow these 6 steps - state the operating conditions clearly → determine the mode of action (single/double-acting) → determine the series (AT, GT, AW, A, ST-series linear, G series hydraulic) → calculate the torque and determine the size (leave a safety factor, calculate at the lowest air pressure, verify the ISO 5211 and NAMUR interfaces) → complete the accessories (solenoid valve, positioner, limit switch, FRL unit, manual mechanism) → verify delivery and test the action. With clear operating conditions and an orderly sequence, selection is fast and accurate.
Conclusion
The key to rapid selection is not rich experience but complete information and a correct order: safety first (mode of action), then capability (torque and size), and finally the supporting items (accessories and interfaces). Master this process and most general operating conditions can be selected in one go and installed successfully in one go. If you need selection calculation and technical solutions for specific operating conditions, please feel free to contact our service team - tell us the medium, temperature, diameter, pressure and safety requirements and you will receive a corresponding model recommendation.
Zhejiang Huaershi Auto-control Instrument Valve Co., Ltd.
Since 1989 · 30+ years focused on pneumatic actuators and pneumatic valves
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