Rotork CMA Precision Modulating Electric Actuator

Overview

The Rotork CMA range is a family of compact, precision modulating electric actuators for linear, part-turn and multi-turn applications that require exact position control and continuous modulation. Rotork offers a CML linear unit, a CMQ part-turn unit and a CMR multi-turn unit, all built on a brushless DC motor and an encoder-based position system. For plants that want to remove compressed air from small and medium control valves, the Rotork CMA offers a direct electric alternative that responds smoothly, without the slip-stick behaviour of a spring diaphragm actuator.

Seven Star LLC supplies the Rotork CMA for control valve, damper and pump-stroke automation across the Sultanate of Oman and the GCC. Our Muscat engineers help to compare sizes against valve thrust or torque, confirm supply voltage options and plan the control interface so that the electric actuator integrates cleanly into the existing DCS or PLC loop.

Operating Principle

In the Rotork CMA, a high-efficiency brushless DC motor drives a durable, lubricated-for-life spur gear train. Thrust or torque is delivered instantly to the valve, which is why the response is smooth and free of stick-slip. The motor is rated for S9 (IEC 60034) or Class D (EN 15714-2) duty, so continuous modulation does not shorten life, and standby power consumption is below one watt.

Position is read by an absolute encoder on the final output drive, with 12-bit resolution for part-turn and linear units and 10-bit for multi-turn units. Placing the sensor on the output removes any internal backlash from the measurement. The self-locking CML and CMQ actuators include an anti-backdrive mechanism that resists up to 125 percent of rated thrust or torque, so process pressure on the valve cannot move it once the actuator has reached the demanded position.

Engineering Design of the Rotork CMA

The Rotork CMA includes a built-in HMI with field-selectable deadband, zero and span, command signal type and direction, together with two programmable relays for digital indication. A hand drive is provided as standard so that the valve can be operated manually, and an optional local controls module adds a selector, an LED backlit display with position in 0.1 percent steps and fault symbols. Speed can be reduced to 50 percent in one percent increments, and operating time values are tabulated for each model by the manufacturer.

The CML-1500 and CML-3000 extend the range for larger control valves, with a ball screw drive train, seating thrust up to 4,500 lbf (20 kN) and modulating thrust up to 3,000 lbf (13.3 kN). Rotork notes that the CMA range can be mounted in any orientation, is explosion-proof to international standards, and can be supplied for single-phase or DC supplies. A CMQ base conforms to MSS SP-101 or ISO 5211, while CML and CMR can be adapted to suit individual valves.

Key Features

The Rotork CMA range combines accuracy with compact size. Key features of the Rotork CMA include:

• Accurate and repeatable position control with up to 0.1 percent accuracy from a 4-20 mA signal.
• Brushless DC motor with maintenance-free, S9 or Class D continuous modulation capability.
• Linear (CML), part-turn (CMQ) and multi-turn (CMR) versions that share one platform.
• Absolute encoder technology on the output drive, with no internal backlash effect.
• Built-in HMI for quick set-up, and optional integral local controls with a position display.
• Optional Reserve Power Pack using super capacitors for fail-to-position functionality.
• Self-locking anti-backdrive that resists up to 125 percent of rated load on CML and CMQ models.
• Communication options including Pakscan, HART, Foundation Fieldbus, Profibus, DeviceNet and Modbus, and RIRO for discrete hardwired control.

Industrial Applications

The Rotork CMA is used on globe and cage-guided control valves, rotary control valves, dampers and variable-stroke pumps, where continuous position changes are needed and instrument air is either expensive or unavailable. In Oman, solar-powered pumping stations, wellhead facilities, desalination dosing lines and district-cooling plants can benefit from the electric option, because the actuator draws very little power at rest and needs no tubing. Facilities that need a larger variable-speed drive for gate or butterfly valves may look at the AUMA SDL/SDG, while smaller linear duties may be compared with the ABB RSD50 linear actuator.

Seven Star LLC supplies the Rotork CMA to projects in the Sohar and Salalah economic zones, to utilities and to OEM skid builders, with engineering support in Muscat. Positioner-based control loops such as those that use an Emerson DVC6200 can be retrofitted with the Rotork CMA when the plant wants to eliminate air consumption. We are happy to review your valve list and propose a suitable CML, CMQ or CMR size.

Technical Specifications

The table gives published CMA range data from the Rotork brochure. Full thrust, torque and operating time tables are available for each model.

Request a Quote for Rotork CMA

For a quotation on the Rotork CMA, send Seven Star LLC the valve make, stroke or torque requirement, speed, supply type and signal. Our instrumentation division in Muscat will select the CML, CMQ or CMR size, confirm the fail-to-position option and include the Rotork brochure with the offer. Seven Star LLC supplies Rotork equipment on request with local engineering support across Oman and the GCC, so request your Rotork CMA quotation today.