Brand: IMI STI

IMI STI RTC Scotch Yoke Pneumatic Actuator

Name: IMI STI RTC Scotch Yoke Pneumatic Actuator
Brand: IMI STI
SKU: RTC

Description

The IMI STI RTC is a range of compact pneumatic quarter-turn actuators using a scotch yoke mechanism, with materials selected to withstand hostile environments. The brochure positions the series for onshore and offshore use on the majority of on-off and modulating valves; the RTCH series covers a wide range of valves in all pressure classes.

Seven Star LLC supplies IMI STI actuators from Muscat and sizes the unit against valve torque data before quoting.

A compact carbon steel scotch yoke for on-off and modulating valves

The housing is carbon steel with no cast, grey or ductile iron or aluminium parts, and it is totally sealed and weatherproof, protecting all moving parts. Housing is not under pressure, which reduces leakage points and simplifies maintenance. The scotch yoke is available in canted or symmetrical executions for the ideal torque distribution, with a chromium plated guide bar to absorb transverse forces and high-strength bronze bushings. The cylinder is electroless nickel plated to reduce friction and prevent corrosion.

For spring return units the power module design allows cylinder seals to be replaced safely without spring removal, and the spring compression takes place without removing the cylinder cap and tie rods. Stainless steel travel stops allow fine stroke adjustment between 82 and 98 degrees. Multiple certified lifting lugs balance the centre of gravity, the output has an ISO 5211 flange connection, and a position indicator carries a VDI/VDE 3845 NAMUR drive slot. An integral or declutchable manual handwheel and a full stainless steel version are available on request.

Technical specifications

Parameter	Specification
Type	Scotch yoke quarter-turn, double acting or spring return
Output torque (double acting)	40 Nm up to 6,000 Nm; higher values on request
Spring ending torque (single acting)	40 Nm up to 2,500 Nm; higher values on request
Operating pressure	Up to 12 bar for the double acting version
Supply medium	Air, nitrogen or sweet gas; sour gas version on request
Operating temperature	-30 to 100 degC; high or low temperature design on request
Housing / scotch yoke	Carbon steel housing; alloy steel yoke; steel/bronze/PTFE yoke bushing
Cylinder / piston	Carbon steel cylinder tube (electroless nickel plated); carbon steel piston
Seals / spring	NBR O-rings; spring steel spring
Mounting	ISO 5211 flange; VDI/VDE 3845 NAMUR position indicator slot
Certifications	PED 2014/68/EU; ATEX 2014/34/EU; EAC TR TS 012/2011; Machinery Directive 2006/42/EC; IP66/67M; SIL3 (IEC 61508) as a single device; EN 15714-3

Sizing and ordering notes

Provide valve breakaway, running and end torques with safety factor, valve type and size, ISO 5211 flange size and stem drive, supply pressure and medium, double acting or spring-return fail direction, ambient temperature range, and whether a handwheel, positioner or limit switches are fitted. For larger torque the manufacturer lists the RTQ series, which is described on a separate page of this site.

Documents and quotation

To request a quotation for the RTC 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.

Browse the valve actuators category for related products.

Datasheets & Documents

Brochure IMI STI RTC Scotch Yoke Pneumatic Actuators Brochure (07043.03/24en) Download

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About brand

IMI STI is an Italian manufacturer of pneumatic, hydraulic and direct-gas valve actuators, valve positioners and actuator accessories. It is based in Levate, near Bergamo, and is part of the IMI plc group (IMI Process Automation).

Seven Star LLC is an independent supplier in Muscat. We list IMI STI positioners, actuators and switches for valve automation in Oman and the GCC and source them by full model code.

IMI STI company profile

Established	1960, in Gorle (Bergamo), Italy
Manufacturing site	Levate (Bergamo), Italy, since 2014. The plant is about 15 km from the original Gorle site.
Group	IMI plc, Process Automation division. STI S.r.l. is the legal entity and IMI STI is the brand name.
Product families	Quarter-turn Scotch yoke actuators, linear actuators, lift-and-turn actuators, stepper actuators, valve positioners, limit switches, pressure switches and pneumatic accessories
Typical duty	Emergency shutdown and isolation valves, anti-surge valves, turbine bypass and steam valves, dampers and process control valves
Industries	Oil and gas, power, petrochemicals, process industries, water and metals

Milestones

1960: STI is founded in Gorle, Bergamo.
2002: IMI plc acquires STI, according to the company's own literature.
2014: Manufacturing moves to the new plant in Levate, about 15 km from Gorle.

IMI STI product series

Series	Type	Key published data
RTC	Pneumatic Scotch yoke quarter-turn actuator	Up to 12 bar supply, -30 to +100 °C ambient, 90° rotation; single-acting, double-acting or spring-return; air, nitrogen, sweet or sour gas; ISO 5211 mounting; SIL 3, ATEX, PED, IP66/67M
RTQ	High-torque pneumatic Scotch yoke actuator	For large ball, plug and butterfly valves in harsh environments; canted or symmetrical yoke
RTQD / RTQH	Direct-gas and hydraulic Scotch yoke actuators	RTQD: gas-over-oil, operating pressure up to 114 bar, -20 to +100 °C; RTQH: hydraulic version for sites with a hydraulic power supply
SC/V, SC	Pneumatic linear actuators	For globe and gate valves (SC/V) and for dampers (SC); SC/VLT is the lift-and-turn version
SHP	Smart high-performance positioner	HART 7, self-tuning, Cv up to 2.3, 2.5 to 10.5 bar supply, ATEX and IECEx, IP66 aluminium or stainless steel housing
SHP-SIS	Safety positioner	IEC 61508:2010 up to SIL 3, built-in partial stroke testing, -55 to +85 °C ambient
FasTrak FT, QuickTrak	Smart digital positioners and valve control systems	Digital positioning with valve diagnostics
SA/CL	Analog positioner	Analog positioner for control valve actuators
2130	Limit switch box	Position feedback for rotary valve actuators

Scotch yoke actuators give their highest torque at the start and end of the stroke. That is where a ball, plug or butterfly valve needs the most break-out and seating torque, so a Scotch yoke can be smaller than a rack-and-pinion actuator for the same valve. A canted yoke moves the torque peak toward one end of the stroke, for valves whose highest demand is when they close. A symmetrical yoke gives the same curve in both directions.

Where IMI STI products are used

In the GCC, IMI STI actuators and positioners appear mostly on emergency shutdown (ESD) and blowdown valves, compressor anti-surge valves, steam turbine bypass valves and large dampers in oil and gas, refining, petrochemical and power plants. On shutdown valves the SHP-SIS positioner adds partial stroke testing, so the valve can be proven to move without taking the plant down.

Ordering and replacement: what we need

For an actuator, send the full model code from the nameplate, the valve type and size, required torque or thrust with safety factor, supply medium and pressure, fail position (fail-close, fail-open or fail-last), stroke time, mounting flange (ISO 5211) and stem adaptor, ambient temperature range and the hazardous-area certification required. For a positioner, send the model, actuator type, signal (4-20 mA, HART), whether partial stroke testing or a SIL rating is needed, and the cable entry thread. When a series has been superseded, we quote the successor that IMI names in its documentation and point out any differences in mounting or signal.

Facts checked against IMI Process Automation product pages and published company history, October 2026.

Browse IMI STI products by category: Valve Positioners, Valve Actuators.