AUMA GST Spur Gearboxes (Multi-Turn)
Overview: Repositioning the Drive Axis for Restricted Installations
The AUMA GST Spur Gearbox is an offset-axis multi-turn gearbox used when an AUMA SA multi-turn actuator’s drive shaft needs to be positioned clear of the valve’s output drive shaft, whether due to space constraints, access requirements, or valve orientation. Combining an SA actuator with a GST gearbox not only repositions the drive axis but also multiplies the output torque significantly beyond what the actuator alone could deliver, extending AUMA’s multi-turn actuator range up to combined torques of 16,000 Nm.
As a trusted supplier of AUMA valve gearboxes, Seven Star LLC sources and supplies the GST spur gearbox to power plants, water treatment facilities, and heavy industrial process plants across Oman and the wider GCC. Because SA/GST combinations solve both torque-extension and installation-geometry problems simultaneously, Seven Star LLC helps engineering teams specify the correct gearbox reduction ratio and mounting configuration for their project.
Working Principle: Torque Multiplication Through Gear Reduction
The GST gearbox uses a spur gear train to transmit rotational drive from the multi-turn actuator to the valve stem, with the gearbox’s reduction ratio – supplied in staged steps of 1:1, 1.4:1, 2:1, 2.8:1, 3:1, 3.28:1, 4:1, 5.6:1, 7:1, 8:1, 9.25:1, 11:1, 14.33:1, 16:1 and 22:1 according to gearbox size, rather than as a continuous range – determining how much the actuator’s input torque is multiplied at the output while proportionally reducing output speed. This is the same fundamental gear-reduction principle used across mechanical power transmission, applied here specifically to valve automation duty where reliability, corrosion resistance, and precise manual operation matter as much as raw torque multiplication.
The GST gearbox shifts the multi-turn actuator physically out of the valve stem axis, which is particularly valuable where restricted access around the valve would otherwise make actuator mounting or handwheel operation difficult; by offsetting the actuator, operators retain free access to the actuator handwheel and controls even in tight installation environments. GST gearboxes with a 1:1 reduction ratio are also available for smaller torques up to 120 Nm, addressing special installation applications where axis offset is needed but torque multiplication is not.
It is worth being precise about what a spur gearbox is, because the three AUMA gearbox families solve different problems. A GK bevel gearbox turns the drive direction through 90°; a worm or part-turn gearbox such as the GS range converts continuous input rotation into a limited 90° travel for butterfly and ball valves. The AUMA GST Spur Gearbox does neither: it keeps input and output rotation on parallel axes and simply displaces the drive axle sideways while multiplying torque, so the valve still receives the many turns of rotation that a rising-stem gate or globe valve requires. AUMA states the relationship plainly in its operation instructions — the drive axle operates at an offset to the output drive axle.
Engineering Design of the GST Gearbox
The GST gearbox is built with a stainless steel input shaft and top-quality corrosion protection using AUMA’s powder coating system, rated IP68 for reliable operation in wet, humid, or submerged installation environments. The gearbox is suitable for both manual and electrical operation, supporting valve commissioning and emergency operation independent of actuator power.
Configuration options include a square adapter for the input shaft, a stem nut version for use as a screw jack, a stem protection tube, position and end-position signaling during manual operation, a second shaft end with or without protective cap, ATEX approval for hazardous-area installations, and high- or low-temperature versions for extreme ambient conditions. This breadth of options allows the GST platform to be adapted to a wide range of project-specific mounting and signaling requirements.
Key Features
The AUMA GST Spur Gearbox extends multi-turn actuator capability for demanding torque and installation requirements. Key characteristics include:
- Torque capacity up to 16,000 Nm when combined with an AUMA SA multi-turn actuator.
- Staged reduction ratios from 1:1 to 22:1, the available steps depending on gearbox size.
- Offset drive axle shifts the actuator out of the valve stem axis for restricted-access installations; a 90° change of drive direction requires an AUMA GK bevel gearbox instead.
- Stainless steel input shaft with IP68 protection and AUMA powder coating corrosion protection.
- Suitable for both manual and electrical operation.
- Optional ATEX approval, stem protection tube, position signaling, and high/low temperature versions.
- Explosion-protected versions to ATEX 2014/34/EU, classified II2G c IIC T4 and II2D c T130 °C as standard.
- Handwheels to EN 12570 from 200 mm to 500 mm diameter, aluminium as standard, with a lockable option and a WSH limit switching device for position and end-position signalling.
- Valve attachment forms A, B1, B2, B3 and B4 to EN ISO 5210, plus DIN 3210 and DIN 3338 forms.
Service Conditions, Duty and Valve Attachment
The GST is rated for short-time duty S2 of 15 minutes in open-close service and intermittent duty S4 at 25 percent for modulating service, and it may be mounted in any position. Maximum permissible input speed is 240 rpm, whether driven by a multi-turn actuator or by a power tool on a square input shaft. In the standard build, clockwise rotation at the input shaft produces clockwise rotation at the output drive; where the opposite sense is needed on sizes GST 10.1 to GST 30.1, AUMA supplies a GW 14.1 reversing gearbox. Valve attachment follows forms A, B1, B2, B3 and B4 to EN ISO 5210, with A, B, D and E to DIN 3210 and C to DIN 3338 also available, alongside the special AF, AK, AG, IB1, IB3 and IB4 forms.
Enclosure protection is IP68 to IEC 60529, which under AUMA’s own definition means a maximum 8 m head of water, continuous immersion for up to 96 hours and up to ten operations while immersed, with modulating duty not recommended during immersion. Corrosion protection is grade KS as standard — suitable for areas of high salinity, almost permanent condensation and high pollution — with grade KX available for extremely high salinity, a distinction that matters directly for coastal installations at Sohar, Duqm and Salalah. The finish is a double-layer powder coating over a two-component iron-mica combination in AUMA silver-grey, similar to RAL 7037. Standard ambient temperature is −40 °C to +40 °C, with −40 °C to +60 °C, −60 °C to +60 °C, −40 °C to +80 °C and 0 °C to +120 °C versions available, and the gearboxes meet or exceed the lifetime requirements of EN ISO 22109.
Industrial Applications
The GST gearbox is deployed wherever gate valves or globe valves require multi-turn actuation with either higher torque than a standalone actuator provides or a repositioned drive axis due to installation constraints, including power plants (conventional, hydroelectric, geothermal, and solar thermal), water and sewage treatment plants, and general heavy process industry. Its combination with AUMA SA actuators makes it a standard solution for extending torque range across AUMA’s broader valve automation portfolio.
Seven Star LLC supports power generation engineering teams, water authorities, and industrial plant maintenance departments across Oman, Muscat, Sohar, and the broader GCC region with sourcing of AUMA GST spur gearboxes, helping projects solve both torque and installation-geometry requirements in a single proven combination.
Technical Specifications
The table below summarizes the core specifications of the AUMA GST Spur Gearbox as supplied by Seven Star LLC.
| Parameter | Specification |
|---|---|
| Model | AUMA GST 10.1 – GST 40.1 |
| Type | Offset parallel-axis spur gearbox (multi-turn); single stage GST 10.1–16.1, double stage GST 25.1–40.1 |
| Torque Capacity | Up to 16,000 Nm (combined with SA actuator) |
| Reduction Ratios | Staged: 1:1, 1.4:1, 2:1, 2.8:1, 3:1, 3.28:1, 4:1, 5.6:1, 7:1, 8:1, 9.25:1, 11:1, 14.33:1, 16:1, 22:1 (by size) |
| Input Shaft | Stainless steel |
| Protection Class | IP68 |
| Corrosion Protection | AUMA powder coating (top quality) |
| Operation | Manual and electrical (via combined actuator) |
| Type of duty | S2 – 15 min (open-close); S4 – 25 % (modulating) |
| Max. input speed | 240 rpm |
| Valve attachment | A, B1, B2, B3, B4 per EN ISO 5210; DIN 3210 / DIN 3338 forms |
| Mounting position | Any |
| IP68 definition (AUMA) | Max 8 m head of water, 96 h continuous immersion, up to 10 operations immersed |
| Corrosion protection grade | KS standard; KX option |
| Coating / colour | Double-layer powder coating, two-component iron-mica; AUMA silver-grey (similar to RAL 7037) |
| Ambient temperature | −40 °C to +40 °C standard; options to −60 °C / +120 °C |
| ATEX classification | II2G c IIC T4; II2D c T130 °C (T3 / T190 °C and IM2 c options) |
| Lifetime | Meets or exceeds EN ISO 22109 |
| Options | ATEX approval, stem protection tube, position signaling, high/low temperature versions |
Request a Quote for AUMA GST Spur Gearboxes (Multi-Turn)
Seven Star LLC supplies the AUMA GST spur gearbox with full manufacturer documentation and regional technical support. Contact our instrumentation and valve automation division for a formal RFQ, to confirm the correct reduction ratio and mounting configuration for your gate or globe valve, or to obtain the complete technical datasheet. Seven Star LLC ensures every unit shipped across Oman and the GCC is genuine, correctly configured, and backed by local engineering support.
For complete actuator and gearbox packages, see the AUMA GK bevel gearbox.
Related Products
- Datasheet AUMA GST 10.1 - GST 40.1 Datasheet Download
AUMA actuator and gearbox types
SA multi-turn actuators handle open-close duty on gate and globe valves, and SAR is the modulating version; the listing includes the SA 07.2, SA 10.2 and SA 25.1. SAEx and SAREx are the explosion-proof equivalents. Part-turn duty on ball and butterfly valves is covered by SQ and the modulating SQR, or by an SA actuator combined with a GS part-turn gearbox. LE linear thrust units convert multi-turn output to thrust, and GHT multi-turn gearboxes extend the torque range up to 120,000 Nm. PROFOX is the compact actuator line. Special items include the seawater-resistant SGM and SGMR part-turn actuators with bronze housings, the SVC and SVCR globe valve actuators and the FQM fail-safe unit. Integral controls come as AM or AC versions.Where AUMA electric actuators are used
AUMA actuators are found in water, power, oil and gas, marine and general industry. In practice that means isolation and control valves in water treatment and pumping stations, power plant steam and cooling systems, tank farms and pipelines, and sluice gates and dampers.Ordering AUMA actuators and parts: what we need
For a replacement send photos of the actuator, motor and controls nameplates: type, order number, serial number and wiring diagram number. For a new actuator we need:- valve type, required torque or thrust, and turns or stroke
- valve mounting flange and stem or shaft details
- output speed, duty (open-close or modulating)
- supply voltage and frequency, control signals or fieldbus
- enclosure protection, ambient temperature, Ex requirement
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