IMI STI SC Pneumatic Linear Damper Actuator

The IMI STI SC is a complete line of linear pneumatic actuators designed for dampers, louvres, butterfly valves and ball valves. The range is made up of double acting units in different sizes and suits power plants, refineries, pipe and steel works and on-board vessels. Seven Star LLC supplies IMI STI actuators from Muscat. Where an inquiry quotes a series number such as 299-22, we ask for the actuator nameplate, because that number is not part of the brochure.

Linear actuators with a built-in lubrication system

The SC series has a patented permanent lubrication system: a grease-filled annular cavity inside the piston, between a sealing ring and a sliding ring, keeps metal parts from touching even under lateral forces on the stem. Smooth operation is maintained with dry instrument air, and no maintenance of moving parts is needed. Further features are a double guide for piston and bushing, no dead volume in the chamber in fully open or closed positions (minimising overshoot), excellent response times without boosters, and an option to assemble a positioner independently of stroke.

Customisable linkages couple the actuator to the control device, a gearbox for emergency manual operation and a high-speed design are available, and customised control panels can be built for remote operation. Sizes run from 63 mm to 420 mm.

Technical specifications

Selecting an SC actuator

Choose bore from the thrust needed at the available supply pressure, then the stroke from the damper or valve travel. Send the load or torque data, supply pressure and medium, stroke, mounting arrangement, ambient temperature, the positioner and accessories wanted, and whether a gearbox override is needed. Control panels and cabinets can be installed on the actuator or supplied loose for remote mounting, which helps limit exposure to heat and vibration. A dedicated accessories brochure exists at the manufacturer.

How the IMI STI SC works

The SC is a double-acting pneumatic linear actuator. Air pressure on one side of the piston moves the stem out, and air on the other side moves it back, so the actuator opens and closes dampers, louvres, butterfly valves and ball valves through a linkage. Inside the piston there is a grease-filled annular cavity between a sealing ring and a sliding ring, which keeps metal parts from touching under side loads on the stem. There is no dead volume in the chamber at the end positions, which limits overshoot.

Where the IMI STI SC is used

• Power plants.
• Refineries.
• Pipe and steel works.
• On-board vessels.
• Damper and louvre control in air and gas ducts.

Selection checklist for the IMI STI SC

• Bore size of 63, 100, 125, 160, 200, 260, 330, 390 or 420 mm.
• Standard stroke of 150, 200, 250 or 300 mm.
• Thrust at 0.5 MPa, from 1,400 N for the 63 mm to 68,000 N for the 420 mm.
• Operating pressure up to 10 barg.
• Operating temperature of -20 to 70 degrees C as standard.
• Aluminium cylinder for 63 and 100 mm, and carbon steel for larger bores.
• Chromium plated alloy steel shaft.
• Positioner mounting independent of the stroke.
• Linkage to suit the damper or valve.
• Gearbox for emergency manual operation, if needed.

Installation, commissioning and maintenance notes

Supply dry instrument air at a pressure that gives the thrust that the damper or valve needs, with a margin. Fit the linkage so that the movement of the damper matches the stroke of the actuator. Connect the positioner or the solenoid valve as the control scheme needs. The permanent lubrication system means that no maintenance of the moving parts is needed in normal use.

Requesting a quotation for the IMI STI SC

Send the bore, the stroke, the air pressure and the control device. Where the inquiry quotes a series number, send the nameplate of the actuator. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

Thrust and sizing

The thrust grows with the active area. At 0.5 MPa, the 100 mm size gives 3,700 N and the 200 mm size gives 15,000 N.

Response and positioner options

The design gives good response times without boosters, and a positioner can be assembled independently of the stroke.

Customised options

The range has customisable linkages, a gearbox for emergency manual operation, a high-speed design and customised control panels for remote operation.

Actuator records

Record the nameplate data, the damper it drives and the air supply pressure.

Choosing the right actuator for a damper

Find the torque or force that the damper needs, including friction and the pressure of the gas on the blade, then choose the bore whose thrust at your air pressure covers it with a margin. Check the stroke against the movement of the linkage, and confirm the temperature of the site. For a tropical site, ask for the tropicalized version where the brochure lists it.

Cylinder materials

The cylinder is aluminium alloy for 63 to 100 mm and carbon steel, chrome or nickel plated, for 125 to 420 mm.

Documents and quotation

To request a quotation for the SC damper actuator, send Seven Star LLC the full model or order code, quantity, and any nameplate data from an existing unit that is being replaced or matched. Our Muscat team checks the request against the manufacturer document, which can be downloaded from this page, and replies with a formal quotation. Prices, stock and lead times are confirmed per inquiry.

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