AT-SR Spring Return Pneumatic Actuator: Converting Manual Ball and Butterfly Valves to Fail-Safe Automation for Oil & Gas
Converting a manual ball valve or butterfly valve starts with one question: what should the valve do when air is lost? The AT-SR spring return actuator answers with spring force — single-acting, 90° rotation on 5-8 bar air, ISO 5211 mounting and NAMUR interfaces, so the valve returns to its safe position when air or control power fails.
Key takeaways
- The existing valve body usually stays: the AT-SR bolts onto its ISO 5211 pad through a bracket and coupling.
- Spring return gives a defined fail close (FC) or fail open (FO) position when air or the signal is lost.
- Size on both air torque and spring torque at start and end positions.
Why are oil and gas operators converting manual valves?
On wellheads, gathering stations and tank farms, a handwheel means an operator walks to the line for every open, close and drain. Around hydrocarbons that carries three costs:
- Personnel exposure. Hand operation puts a person next to pressurised, flammable media — where nobody should stand during an upset.
- Shutdown reliability. An emergency shutdown (ESD) philosophy expects the valve to reach its safe state even when instrument air or power is already gone.
- Consistency. Operator strength and speed vary; seat torque does not. Half-closed valves chew seats.
Because the AT-SR mounts on the standard ISO 5211 / DIN 3337 interface, the existing valve body is usually kept and only the actuation is added.
How does a spring return actuator make a valve fail safe?
A double-acting actuator moves only while air is applied. A single-acting spring return actuator stores the return stroke in a spring set: when air pressure drops below the spring force, the pistons travel to the spring-side end and the valve rotates to its fail position — fail close or fail open, depending on the assembly direction on the valve stem.
Choose the fail position during the plant's safety review — fail close for feed and product lines that must stop flowing, fail open for vents, cooling and relief routes. Then verify both datasheet numbers: air torque at the available supply pressure, and spring torque at both stroke ends, so the spring still seats the valve against line pressure with margin.
Which AT-SR model fits the valve?
Sizing follows the valve, not the actuator. Take the valve break and running torque from the valve maker, apply the site safety factor, then compare with the AT-SR quick reference at 5 bar:
| Model | Spring set | Air torque at 5 bar, start/end (N·m) | Spring torque 90°/0° (N·m) | ISO 5211 flange |
|---|---|---|---|---|
| AT-50S | 6 springs | 13.9 / 11.1 | 7.2 / 4.4 | F03/F05 |
| AT-50S | 10 springs | 10.9 / 6.3 | 12 / 7.4 | F03/F05 |
| AT-63S | 6 springs | 24.4 / 19.5 | 12.7 / 7.8 | F03/F05 |
| AT-160S | see catalog p. 90 | catalog p. 90 | catalog p. 93 | F10/F12 |
More springs mean less air torque but more spring torque — exactly the trade a fail-safe application sizes. The same logic repeats across AT-75S, AT-100S and AT-125S; full tables sit on catalog pages 89-94. Ball and butterfly valves have different torque curves, so send the valve datasheet rather than sizing from pipe size alone.
What does a manual-to-pneumatic conversion involve?
| Step | What to check | AT-SR reference |
|---|---|---|
| Mounting | ISO 5211 / DIN 3337 pad, stem height and shape | F03/F05 to F10/F12 flange, bracket and coupling |
| Air supply | 5-8 bar at the valve (10 bar max), dry air | Operating pressure 5-8 bar per ISO 8573-1 |
| Pilot valve | 3/2-way solenoid, single-acting duty | VDI/VDE 3845 NAMUR side interface |
| Position feedback | Limit switch box or positioner | VDI/VDE 3845 NAMUR top interface |
| Travel stops | Open/close setting | Two independent ±5° adjusters |
| Environment | Site temperature, medium | NBR standard, FKM/silicone optional; -20/+80 °C std, -35/+80 °C or -20/+150 °C options |
Two retrofit notes: if the old valve has no ISO 5211 pad, send its model or nameplate photo — the published RFQ guidance asks for exactly that. The coated high-alloy spring steel with a 1,000,000-cycle rating suits outdoor oil and gas sites.
What should the RFQ state?
| Field | Example |
|---|---|
| Model | AT-63S — or ask us to size it |
| Fail position | Fail close / fail open |
| Valve data | Type, torque, safety factor, air pressure |
| Quantity | Pieces and delivery terms |
Frequently asked questions
Can I convert my existing manual ball valve, or do I need a new actuated valve?
Usually the valve stays. If it carries an ISO 5211 pad (DIN 3337 on older bodies), the AT-SR mounts through a bracket and coupling machined to the stem. Send the nameplate and stem dimensions for confirmation.
Fail close or fail open — who decides?
The plant's safety study decides; the assembly direction implements it. Feed-line isolation valves are normally fail close, vents and cooling lines fail open. Confirm before ordering — it fixes the spring set and the arrangement.
What air supply does the AT-SR need?
5-8 bar operating pressure, 10 bar maximum, at 90° ±5% rotation. Check both air torque and spring torque at your actual supply pressure before finalising the size.
Ningbo Kailing Pneumatic Co., Ltd has manufactured the AT series actuators, solenoid valves and angle seat valves since 2003. Send the valve model, medium, fail position, air pressure and quantity — we will confirm the spring set, flange and accessories before quoting — or start from the AT-SR product page.
Need a quotation?
Send the page link, quantity, drawings and working conditions to Kailing for review.