IMI STI CML Compact Control Drive Pneumatic Actuator

CML compact enclosed control drive with automatic engaged manual override

The IMI STI CML is a pneumatic control-drive actuator that packages a double acting cylinder, a lever mechanism and a manual override inside a portable carbon-steel housing. It is intended for angular control of dampers, butterfly valves, speed variators and radial vanes, where the load needs small to medium torque, up to 100 daNm, and where the equipment must work reliably in dusty, hot or otherwise harsh locations. Seven Star LLC supplies the CML in Oman and the GCC as an independent supplier in Muscat.

The drive is built around a linear actuator from the IMI STI SC series, with the manufacturer permanent-lubrication system built into the piston. The linear stroke is converted into an angular movement of an output shaft through a lever. The manual describes an operating angle of 90° for the CML-1 and 70° for the CML-2 size, which matches the brochure angles for each size.

CML actuator sizes and available torque

The CML range comes in two series and four cylinder and stroke combinations. The torque figures below are stated for an air supply of 0.50 MPa and an operating angle of 70° or 90° at the final element, in daNm.

Cylinder 63/125 and 100/100 use a 90° working lever angle, while 100/200 and 125/200 use 70°. The product page lists the largest cylinder diameter as 125 mm and the maximum stroke as 200 mm, which matches the CML-2 125/200 unit. The maximum operating air supply pressure given in the brochure footnote is 0.44 MPa for the torque table

CML technical specifications

The certifications are as listed on the manufacturer product page for the series. They depend on the build, so state the required marking on the enquiry.

How the CML manual override works

For manual operation, the lever is clutched onto the splined shaft end, the air supply valve to the actuator is closed and a by-pass valve between the two cylinder chambers is opened, which balances the pressure and frees the piston. The operator moves the damper or valve with the lever and fixes it with a mechanical lock lever when the target position is reached. The splines allow the lever to be orientated for convenience. The result is a drive that can be controlled by instrument air in service and by hand during commissioning, maintenance or loss of air.

An optional balancing security sensor (BSS) is mentioned in the brochure: it automatically switches from manual to modulating mode only when the control signal matches the position at which the actuator is locked, preventing a sudden jump when the lock is released.

Lubrication system and construction of the CML

The cylinder piston carries a grease-filled annular cavity between a sealing ring and a sliding ring. During movement the grease keeps the metal surfaces apart, even with side loads on the stem, which gives smooth sliding even on dry instrument air and a long seal life. According to the manufacturer this removes the need for line lubricators and for routine lubrication of the moving parts inside the cylinder. The housing is both protective cover and load-bearing frame, so no extra supports are needed. Large removable panels with quick fasteners give access for inspection, and an internal panel is available for mounting accessories.

Accessories and related IMI STI products for the CML

The CML is compatible with a wide range of positioners and accessories fitted inside the housing: pneumatic or electro-pneumatic positioners, solenoid valves, air-lock devices, limit switches and position transmitters. The brochure suggests the SHP smart positioner. Related IMI STI actuators on the same technology are the SC series and SC/VLT lift-and-turn actuator, as well as the scotch-yoke RTC and RTQ ranges for valve quarter-turn duty. The air-lock holds the actuator in place when the air supply falls below a set point.

Selection and ordering checklist for the CML

• Series and size: CML-1 or CML-2, and the cylinder and stroke combination.
• Required torque at the operating angle, with allowance for the load, seat or damper characteristics.
• Angle: 70° or 90°, which is set by the size.
• Air supply pressure within 7 to 10 barg, with a regulator if the plant supply is higher.
• Positioner and accessory package: positioner type, solenoid, air-lock, limit switches, transmitter.
• Tubing and fitting material: brass and copper or stainless steel 316.
• Ambient temperature range and any low or high temperature option.
• Painting and certification requirements.

Installation, start-up and maintenance of the CML

Store the drive in a dry, clean place until it is installed. Fit a filter or filter regulator with a 5 micron cartridge and a shut-off valve on the supply, and a pressure regulator set to about 7 bar when the plant air can exceed the maximum. The actuator is fastened with four screws through the rear knuckle onto a flat surface. After installation check alignment with the load and make sure there is no binding, sticking or jumping through the full stroke. Then raise supply pressure gradually to the operating value.

The manual gives a simple schedule: lubricate the external moving parts such as the clevis and knuckle pins every six months if needed, grease the shaft bearing at least once a year through the grease nipple, and every two to three years replace gaskets and refill or replace lubricant, depending on the severity of service.

Typical CML applications in Oman and the GCC

The manufacturer names power stations, steel industries, petrochemical plants and desert areas. In Oman and the GCC the CML suits air and flue damper control in power and boiler plants, radial vane and louvre control on fans, and butterfly valves on large cooling water or ducting lines. The enclosed housing keeps sand and dust away from the linkage and accessories, and manual override helps on outdoor equipment when air or power is lost.

Information to send with a CML request

• Part name CML, series, cylinder and stroke, and quantity.
• Torque required, with load data for the damper or valve.
• Supply pressure range and air quality.
• Positioner, solenoid and limit switch needed.
• Ambient temperature, area classification and certification requirement.
• Mounting arrangement and lever orientation.

Documents and quotation

The IMI STI product brochure for the CML series is attached on this page, with the torque table, specifications and features summarised above.

Send the part number, size and the load data to Seven Star LLC and we will confirm lead time and any other available documents, such as the instruction manual, for the CML.