Brand: IMI STI

IMI STI RTQ High-Torque Scotch Yoke Pneumatic Actuator

Name: IMI STI RTQ High-Torque Scotch Yoke Actuator
Brand: IMI STI
SKU: RTQ

Description

The IMI STI RTQ is a range of high-torque pneumatic quarter-turn actuators with a scotch yoke mechanism and materials chosen for hostile environments. The brochure lists output torque from 2,000 Nm up to 600,000 Nm, which places the RTQ above the RTC series for large valves in onshore and offshore service; the RTQH series is designed to cover a wide range of valves in all pressure classes.

Seven Star LLC supplies IMI STI actuators from Muscat and works from the valve torque data to confirm the model.

A modular welded carbon steel scotch yoke for large valves

The housing is welded carbon steel with no cast, grey or ductile iron or aluminium parts. It is totally sealed and weatherproof, internally coated, and has multiple lifting lugs positioned to balance the centre of gravity. Spring-return and double-acting units share a modular design: power and spring modules are interchangeable, so the fail-safe mode can be reversed quickly and without danger. Spring containers keep the spring pack inherently safe, and controlled tightening torques and zero clearance between mechanical components are used on all threaded couplings.

The scotch yoke is available canted or symmetrical, with a chromium plated guide bar and piston rod, bronze bushings and sliding blocks and an electroless nickel plated low-friction cylinder. Cylinder design allows all pneumatic seals to be replaced in the field, and stainless steel travel stops give fine angular stroke adjustment between 82 and 98 degrees. The output has an ISO 5211 flange connection, the position indicator carries a VDI/VDE 3845 NAMUR drive slot, and an integral or declutchable handwheel or hydraulic hand pump, a full stainless steel cylinder and valve adaptation are available on request.

Technical specifications

Parameter	Specification
Type	Scotch yoke quarter-turn, double acting or spring return, modular
Output torque (double acting)	2,000 Nm up to 600,000 Nm; higher values on request
Spring ending torque (single acting)	1,650 Nm up to 165,000 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 / yoke	Carbon steel housing; carbon steel scotch yoke; bronze alloy yoke bushing
Guide bar / piston rod	Alloy steel, chromium plated
Cylinder / piston	Carbon steel; sliding ring PTFE/bronze; NBR O-rings
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

Send the valve maximum torque with safety factor, valve type and size, flange and stem drive data, supply pressure and medium, spring-return or double-acting fail direction, ambient range and the accessories wanted (handwheel or hydraulic hand pump, positioner, limit switches, solenoids). For smaller torque the RTC series is the compact alternative.

Documents and quotation

To request a quotation for the RTQ 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 RTQ Scotch Yoke Pneumatic Actuators Brochure (07046.03/24en) Download

Reviews (0)

Reviews

There are no reviews yet.

How would you rate this product?

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.

FAQ

Questions about the IMI STI RTQ High-Torque Scotch Yoke Pneumatic

Answers from our engineering team on installation, compatibility and integration.

01What torque range does the RTQ cover?

2,000 Nm up to 600,000 Nm double acting, and spring ending torque from 1,650 Nm up to 165,000 Nm.

02How does it differ from the RTC?

The RTQ is the high-torque, modular welded-housing range, while the RTC is a compact range up to 6,000 Nm.

03Can the fail-safe direction be changed?

The interchangeable power and spring modules allow the fail-safe mode to be reversed quickly and without danger, per the brochure.

04What manual override is available?

An integral or declutchable handwheel or a hydraulic hand pump is available on request.

05What is the maximum operating pressure?

Up to 12 bar for the double acting version.