A pneumatic actuator not fully opening or closing generally refers to the valve product it is paired with not fully opening or closing - the common symptom is that it "won't shut off" or "won't open fully". There is more than one reason behind this: it may be an excessive leakage rate, or jamming by foreign matter, the positioner span, differential pressure, selection or output force. This article sorts out the troubleshooting approach and adjustment methods for incomplete opening and closing to help you locate the fault quickly.
1. First Distinguish - Is the Leakage Rate Excessive or Is It Really Not Reaching Position
Before troubleshooting, clarify one concept - the valve paired with a pneumatic actuator (such as a pneumatic shut-off valve) inherently has a certain leakage rate during use:
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If the leakage rate exceeds the value specified by the standard, quality problems such as "won't shut off" are likely to occur
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Before use, be sure to understand the allowable standard for the leakage rate and use the product correctly
If it is confirmed that the problem is not the leakage rate, then continue troubleshooting the mechanical and pneumatic links.
2. Check 1 - The Valve or Valve Stem Is Jammed by Foreign Matter
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Check whether the valve and the valve stem are jammed by foreign matter
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If there is foreign matter, clean it out early to avoid damaging parts by forcing them against each other
3. Check 2 - Insufficient Positioner Span
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Check whether the span of the electrical positioner is set too low
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An insufficient span prevents the valve from reaching the fully open / fully closed position
4. Check 3 - Excessive Differential Pressure
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Check whether the differential pressure across the pneumatic shut-off valve is too high
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Excessive differential pressure makes the actuator "unable to push", causing incomplete opening or closing
5. Check 4 - Selection Problem
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Check whether the selection is reasonable - whether the actuator output force matches the operating force required by the valve
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If the selection is undersized, the actuator naturally "cannot drive" the valve
6. Check 5 - Output Force Too Low (Including Adjustment Tips)
If it is confirmed that the actuator output force is too low, you can increase the output pressure to increase the output force:
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Increase the output pressure (+PF) to raise the actuator output force
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For an air-to-close valve: turn the adjusting element counterclockwise (loosen), i.e. move PO~PL forward
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During adjustment, watch whether the full stroke changes
7. A Quick Troubleshooting Reference
| Troubleshooting direction | What to judge | What to do |
|---|---|---|
| Leakage rate | Whether it exceeds the value specified by the standard | Verify the allowable standard and use the product correctly |
| Foreign matter jamming | Whether the valve / valve stem is stuck | Clean out the foreign matter |
| Positioner span | Whether the span is insufficient | Readjust the span |
| Excessive differential pressure | Whether the differential pressure across the valve is abnormal | Adjust the operating conditions |
| Selection | Whether the output force matches | Re-select |
| Low output force | Insufficient thrust | Increase the output pressure (+PF) |
Conclusion
The recommended troubleshooting order for a pneumatic actuator not fully opening or closing is: check the leakage rate first → then check for foreign matter → calibrate the span → look at the differential pressure → verify the selection → adjust the output force. Most "won't shut off" problems can be resolved in one of these directions. For technical support in adjusting the opening and closing of pneumatic actuators, please feel free to contact our professional service team.
Zhejiang Huaershi Auto-control Instrument Valve Co., Ltd.
Since 1989 · 30+ years focused on pneumatic actuators and pneumatic valves
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