The selection logic that works for ordinary conditions often fails in explosion-proof and wide-temperature applications. The reason is simple: in these applications, what decides success is usually not the actuator itself, but the seal material, the grease type, the electrical accessories and the air supply quality — and these are exactly the things ordinary selection is most likely to skip.
This article separates the two special categories — explosion-proof and wide-temperature — and gives directly actionable selection and configuration approaches.
1. Define the Conditions First: What Makes Explosion-Proof and Wide-Temperature "Special"
Explosion-proof conditions mean an environment contains explosive gas or combustible dust, and the protection rating must be determined by zone classification: gas environments are usually divided into Zone 0, Zone 1 and Zone 2, and dust environments into Zone 20, Zone 21 and Zone 22. Different zones impose different explosion-proof requirements on electrical components.
Wide-temperature conditions mean occasions where the temperature falls outside the normal range, including both the high-temperature and low-temperature sides. When defining them, four points must be stated clearly:
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What the maximum temperature and the minimum temperature are respectively
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Whether it is ambient temperature or medium temperature (the two impose different requirements on seals and grease)
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Whether the temperature changes abruptly (frequent alternating hot and cold greatly affects seal life)
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Whether heat tracing, insulation or thermal isolation must be considered
Only when the conditions are clearly defined will the solution not go wrong.
2. Explosion-Proof Conditions: The Body Relies on Pneumatics, the Focus Is on Electrical Accessories
Because a pneumatic actuator uses compressed air for power, it inherently has the advantage of being fire- and explosion-proof, making it the preferred choice of actuating device for hazardous areas. But choosing pneumatic only solves the power part; the real difficulty of explosion-proofing lies in the accessories and signal circuits:
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Explosion-proof accessories must be selected: solenoid valves, limit switches, positioners and the 4–20mA signal circuits — if any one of them is of the ordinary type, the whole circuit is invalid
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Select by type of protection: flameproof, intrinsically safe and increased safety types each have their applicable occasions; intrinsically safe types also require a safety barrier
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Check three things: the explosion-proof marking and the temperature class (which must match the ignition temperature of the medium), the equipment category (gas and dust, different levels), and the models and applicable areas covered by the explosion-proof certificate
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Wiring and installation: cable entry devices, grounding and connector protection must all be executed to explosion-proof requirements
In one sentence: avoid the combination of "explosion-proof body, non-explosion-proof accessories", because in a hazardous area the weakest link determines overall safety.
3. Wide-Temperature Conditions: The Three Essentials — Seals, Grease and Air Supply
Seal material: nitrile rubber is commonly used at normal temperature; for high temperature, give priority to heat-resistant materials such as fluororubber or PTFE; for low temperature, choose low-temperature-specific materials such as low-temperature nitrile or silicone rubber. If the material does not match, the seals will harden, crack or age prematurely.
Choose grease by temperature: general-purpose lithium grease at normal temperature covers about -20°C to 120°C; polyurea grease for high temperature covers -30°C to 200°C; low-temperature lithium grease covers about -40°C to 80°C. Do not mix different base greases, and remove the old grease completely when changing.
The air supply is the key variable: at low temperature the moisture in the air supply freezes, causing sluggish action or even seizing, so drying and draining must be strengthened; the air supply dew point is usually required to be lower than the lowest on-site ambient temperature. On the high-temperature side, note the distance between the actuator and the heat source, adding thermal isolation or using an extended stem where necessary, so that the cylinder and seals are not kept in an over-temperature state for long periods.
4. The Effect of Wide Temperature on Operating Performance: Torque Must Have Sufficient Margin
Temperature not only affects life but also directly changes the available output:
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At low temperature, seals harden and friction increases, the actually available torque drops, and starting resistance rises noticeably
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At high temperature, grease loss accelerates and seals age faster, the risk of internal leakage increases, and long-term efficiency drops
Therefore the selection principle for wide-temperature conditions is: calculate torque at the lowest and highest on-site temperatures and adopt a more conservative safety factor than for ordinary conditions. Where action speed matters (low-temperature startup, frequent action), a quick exhaust valve and a larger solenoid valve port size should also be considered, and it should be confirmed whether the air supply capacity can keep up.
5. Configuration Checklist: Fit Everything at Once to Avoid On-Site Rework
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Actuator: single-acting or double-acting according to the fail-safe requirement on air loss; rotary or linear according to the valve type
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Explosion-proof electrical accessories: explosion-proof solenoid valve, explosion-proof limit switch, explosion-proof positioner (a safety barrier for intrinsically safe types)
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Air treatment: filter regulator, drying equipment (refrigerated or desiccant), regular draining measures
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Materials and protection: corrosion-resistant materials or coatings, a suitable ingress protection rating, high-/low-temperature-resistant seals and grease
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Temperature measures: heat tracing and insulation of the air supply and piping at low temperature, thermal isolation and an extended stem at high temperature
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Emergency configuration: a manual override to ensure manual operation during a power failure or loss of air
Every item in the checklist should be determined at the selection stage, not added later during on-site installation.
6. Verification and Pitfalls: Check Once Before and Once After Delivery
Checks before delivery: the models and areas covered by the explosion-proof certificate, the temperature class, whether the seal and grease types match the operating conditions, and whether all accessories are of the matching explosion-proof type.
Verification on receipt and before commissioning: shell pressure test and air-tightness leak test (held at rated pressure for 5 minutes, judged acceptable if the pressure drop is no more than 5kPa), full-stroke action test, verification of limit signals and position feedback; where conditions allow, carry out a simulated operating-condition confirmation.
Common pitfalls:
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Choosing only explosion-proof accessories without improving the air supply — moisture in the air supply will still seize the valve at low temperature
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Using normal-temperature grease in low- or high-temperature service — it solidifies when cold and runs off when hot
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Sizing by normal-temperature torque, with no temperature margin — "cannot move it" at low temperature
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Ignoring the match between temperature class and medium ignition temperature — the wrong explosion-proof marking makes it useless
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Ignoring air supply freezing in low-temperature environments — the number one source of winter faults
Key review: for explosion-proof and wide-temperature selection, first define the conditions (zone classification, maximum and minimum temperatures, ambient or medium temperature), then configure along three main lines — explosion-proofing relies on "a full set of explosion-proof accessories + certificate coverage verification", wide temperature relies on "seal material + grease selected by temperature + air supply drying and dew-point control", and torque is calculated at extreme temperatures with a more conservative safety factor; finally fit the air treatment, protective materials, heat tracing and insulation, and manual override together, and verify item by item before and after delivery. Special conditions are not to be feared for their high requirements; what is to be feared is taking them for granted as ordinary conditions.
Conclusion
Selection for explosion-proof and wide-temperature conditions is essentially about translating environmental conditions into specific material, lubrication and accessory requirements: the zone determines the explosion-proof configuration, the temperature determines the sealing and lubrication, and the air supply determines long-term stability. Write these three things into the selection conditions, and the actuator can run reliably over the long term in hazardous areas and at extreme temperatures. For selection calculations and configuration solutions for special conditions, please contact our 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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