IMI STI GR Manual Override for Pneumatic Actuators

IMI STI GR manual override for pneumatic actuators

The IMI STI GR is a handwheel manual override that lets an operator move an actuator stem by hand. Seven Star LLC supplies the IMI STI GR in Oman and the GCC as an independent supplier in Muscat, for control valve packages that must still be operable when instrument air is lost or during commissioning and maintenance.

“GR” is the manufacturer’s model code, and the brochure describes it as a family of gearboxes in four frame sizes: GR 1, GR 2, GR 2.5 and GR 3. Each frame is then offered in several stroke versions, written as GR_ followed by a stroke number (for example GR_153 in the GR 1 or GR 2 frame). The brochure does not provide a long coded ordering string, so the frame and stroke code are the identifiers to confirm with your quotation request.

IMI STI GR technical specifications

How the GR works and what it can do

The override sits in the load path between the actuator and the valve stem, or on the stem cap side, depending on the actuator series. Turning the handwheel drives the stem through an internal gear on ball bearings. The bearings reduce friction, so the operator effort stays low and the gear lasts longer under repeated use. When the actuator is pressurized the handwheel stays out of the way; when air is not available the operator can position the valve manually.

The brochure lists several additional functions. The override can act as an adjustable retraction stroke limiter, which limits how far the stem can retract and so sets a mechanical end stop. An optional adjustable thrust limiter protects the gear and valve from excessive force. A locking mechanism can fix the stem in any position, which is useful when a valve has to be held at a defined opening during maintenance. A chain transmission option lets an operator work the override from a remote or elevated position through a chain wheel, and a sandstorm design adds bellows on the stem and main screw to keep abrasive dust out.

GR frame sizes, strokes and weights

The table summarizes the frame data from the brochure. Weights are in kilograms and the H dimension is in millimetres. Check the dimensional drawing in the attached document for the exact stroke version you need, because weight and height grow with stroke.

Choosing a GR frame

The correct frame follows the actuator and the thrust that the valve can need. The aluminium GR 1 and GR 2 are light, which suits smaller actuators and installations with weight limits. The cast iron GR 2.5 and the carbon steel GR 3 are heavier frames for larger thrust requirements, and their weights of roughly 70 to 240 kg mean that mounting support and lifting must be planned. The stroke code must be at least the actuator stroke you need. Always state the actuator series (SCV or SC), the model and the stroke so that the supplier can match the gearbox correctly.

Selecting and ordering a GR

• Actuator: STI series (SCV or SC), model, stroke and single or double acting action.
• Frame: GR 1, GR 2, GR 2.5 or GR 3, and the stroke code in the GR_xxx format.
• Functions needed: stroke limiter, thrust limiter, locking mechanism, chain transmission, sandstorm bellows.
• Temperature: the standard -20°C to 70°C or one of the wider ranges.
• Environment: offshore or coastal paint requirements, dust exposure, copper-free requirements.
• Operator access: handwheel height, platform, and whether a chain is needed for remote operation.
• Direct-mount application: tell the supplier if the override is meant to drive a valve with no actuator.

Installation, commissioning and maintenance of the GR

The gearbox is fitted between actuator and yoke on SCV series actuators and on the stem cap side for SC series. It should be mounted by technicians with the actuator depressurized and the valve isolated or supported, since the override sits in the stem load path. After installation, stroke the valve under air and check that the handwheel does not rotate when it should not. Then test the manual function through the full travel and confirm the operating direction marking on the handwheel.

In service, the main checks are to keep the thread and bellows clean, to operate the handwheel occasionally so the gear does not seize in standing positions, and to inspect the paint finish so that the carbon steel or cast iron housings do not corrode in coastal air. If a locking device is fitted, make sure operators know the lock must be released before pneumatic operation, otherwise the actuator will fight the lock.

Typical applications in Oman and the GCC

A manual override is expected on many control valves in oil and gas processing, power plants, desalination units and petrochemical sites, where a valve may need to be set by hand during air-supply failures, start-up and shutdown. In the Gulf region, the sandstorm bellows option and the offshore paint specification help protect the stem and gear from blowing dust and salt. The chain option is useful when valves are installed high on pipe racks and operators need to reach the handwheel from the ground.

What to send with a GR request for quotation

• Part number GR, frame size and stroke code.
• Actuator model, series and stroke.
• Required options and temperature range.
• Paint and environment requirements.
• Quantity, delivery location and documents needed.

Documents and quotation

The manufacturer brochure for the IMI STI GR is attached on this page as a PDF, so your engineers can compare it with the data above before ordering. Seven Star LLC is an independent supplier in Muscat and does not act on behalf of the brand, and we do not publish prices online.

To receive a quotation for the IMI STI GR, send the details listed in the previous section by email or through the RFQ form. We reply with availability, lead time and commercial terms for delivery in Oman and across the GCC.