Oil & Gas
Pipeline, refinery, and terminal isolation on butterfly, ball, and gate valves.
Self-locking · Non-backdrivable
Self-locking worm gear operators hold a valve at any position without a separate brake because the worm-and-wheel mesh cannot be back-driven from the output side. This non-backdrivable behaviour prevents reverse valve movement under flow, vibration, or pressure surge. Legacy reference entries (M07–M16, 200–4,400 N·m) deliver self-locking quarter-turn control on ISO 5211 interfaces.
Before you specify
Ask for backdriving behavior to be confirmed for the selected gearbox and service conditions. A self-locking description alone does not establish a safety holding or fail-safe function.
| Selection check | Required input |
|---|---|
| Load | Provide the reverse load, vibration and operating conditions to the supplier. |
| Configuration | Identify the exact gearing, lubrication and installation covered by the confirmation. |
| Holding need | State any independent locking or safety requirement in the enquiry. |
Download selection worksheet (PDF) Check the part-turn interface · Request a configuration review
References: Technical scope and product reference. Manufacturer documents describe their own products; confirm the exact offered configuration.
Application Foundation
A self-locking worm gear operator uses the geometry of the worm-and-wheel set to resist back-driving: torque applied to the valve stem cannot turn the worm in reverse. This means the valve stays exactly where it is set, with no need for a separate brake, detent, or position lock — a key safety property on horizontal stems, large discs, and high-flow lines.
Self-locking depends on the worm lead angle being below the friction angle of the mesh, which holds true across the legacy reference M00 single-stage range (M07–M16). The reference table below lists catalog output torque, ratio, input torque, bore, ISO 5211 flange, and weight for these self-locking quarter-turn models.
Engineering Data
| Model | Output Torque (N·m) | Ratio | Input Torque (N·m) | Max Bore (mm) | ISO 5211 Flange | Weight (kg) |
|---|---|---|---|---|---|---|
| M07 | 200 | 40:1 | 19 | 25 | F05, F07 | 3.1 |
| M10 | 500 | 42:1 | 45 | 30 | F07, F10 | 6.2 |
| M12 | 1000 | 42:1 | 90 | 40 | F10, F12, F14 | 11 |
| M14 | 1800 | 60:1 | 110 | 60 | F12, F14, F16 | 14 |
| M14A | 2500 | 70:1 | 130 | 60 | F14, F16 | 21 |
| M15 | 3400 | 68:1 | 165 | 80 | F14, F16 | 32 |
| M16 | 4400 | 88:1 | 169 | 85 | F16, F25 | 44 |
Third-party benchmark source: legacy third-party reference catalog (M00 single-stage, manual quarter-turn). ValveWormGear does not claim these models as its own offering. Values are catalog nominal figures; final dimensions, ratings and drive details require confirmation from the named supplier — request a datasheet.
| ISO 5211 Flange | Typical Valve Size Band* | Common Valve Families | Reference Entries Offering This Flange |
|---|---|---|---|
| F05 | Small bore | Ball, plug, small butterfly | M07 |
| F07 | Small–medium bore | Butterfly (wafer), ball, plug | M07, M10 |
| F10 | Medium bore | Butterfly, ball, plug | M10, M12 |
| F12 | Medium bore | Butterfly (lug), ball, gate top-work | M12, M14 |
| F14 | Medium–large bore | Butterfly, trunnion ball, gate | M12, M14, M14A, M15 |
| F16 | Large bore | Butterfly (double flange / AWWA), ball, gate | M14, M14A, M15, M16 |
| F25 | Heavy / large bore | Large AWWA butterfly, high-pressure ball, large gate | M16 |
*Valve size band is indicative only — actual flange depends on the valve manufacturer's top-work, stem, and torque rating. Flange and legacy single-stage reference data are from the legacy reference catalog (M07–M16, 200–4,400 N·m). Two-stage and electric-actuator series extend up to 160,000 N·m. Confirm the exact flange against your valve datasheet.
Operation
In a self-locking worm gear operator, the worm drives the wheel but the wheel cannot drive the worm. This one-way behaviour, called non-backdrivability, occurs when the worm thread's lead angle is smaller than the friction angle at the tooth contact. As a result, line pressure, water hammer, or vibration acting on the valve stem cannot rotate the operator backward, and the valve holds its set position.
Self-locking removes the need for an external brake or position lock, simplifying the installation and improving safety on horizontal-stem and large-disc valves. It does trade some efficiency for the locking effect, so operators are sized to the valve break-to-open torque with a documented safety factor to keep handwheel effort within ergonomic limits.
Engineering
By Industry
Pipeline, refinery, and terminal isolation on butterfly, ball, and gate valves.
Intake, distribution, and process isolation valves in municipal and industrial plants.
Cooling-water, feedwater, and circulating-water valve actuation.
Slurry, tailings, and process water valves in abrasive duty.
Common Questions
A worm gear operator is self-locking when the worm thread's lead angle is below the friction angle of the worm-and-wheel mesh. In that condition the worm can drive the wheel, but torque on the wheel cannot turn the worm back. The valve therefore holds position with no separate brake — true across the legacy reference M07–M16 single-stage range.
Yes. Non-backdrivability is the defining feature: pressure, flow, vibration, or water hammer acting on the valve stem cannot rotate the operator in reverse. The valve stays where it is set. This makes self-locking worm gear operators well suited to horizontal stems, large discs, and high-flow isolation where drift is unacceptable.
The worm-and-wheel set is the gear type used for self-locking valve operators. Its sliding mesh and low lead angle give the one-way, non-backdrivable action. Helical, spur, and bevel gears generally back-drive freely, so a worm stage is added when self-locking position holding is required, as in the legacy reference M00 operator range.
Yes. Self-locking operators are common on butterfly valves because the disc generates dynamic torque under flow that would otherwise force the valve toward open or closed. The non-backdrivable worm holds the disc at the set angle. Match the operator to the butterfly valve break-to-open torque and ISO 5211 flange.
Worm gearboxes trade efficiency for their compact high reduction and self-locking action — the sliding mesh generates heat and friction loss compared with helical drives. They are best for intermittent valve duty rather than continuous high-speed power transmission. For valve operators this trade-off is acceptable because position holding and torque multiplication matter most.
Send your valve type, required holding torque, and stem data. Use the cited third-party range only as a preliminary comparison; the named supplier must confirm the final model, rating and non-backdrivability.