Limitorque MXFS/QXFS Fail-Safe Smart Electric Actuator

Overview

The Limitorque MXFS/QXFS is a fail-safe version of the Limitorque MX and QX Series B smart electric actuators. It adds an independent mechanical spring to the electric drive, so the valve is driven to fail-open or fail-closed on loss of power or an emergency shutdown signal without any hydraulic power unit, compressed air or gas-over-oil system. For operators of pipeline ball valves, emergency shutdown (ESD) valves, safety valves, offshore control valves and remote wellhead valves, this gives a clean electric alternative to hydraulic and pneumatic fail-safe packages.

The manufacturer brochure positions the Limitorque MXFS/QXFS as an option on the MXb and QXb actuators, which means the same menus, diagnostics, network options and spare-part philosophy apply. Seven Star LLC supplies the Limitorque MXFS/QXFS from Muscat with engineering support for oil, gas and power customers in Oman and the GCC, and our team can discuss the valve torque, safe position, release method and signal scheme before a quotation is issued.

Fail-Safe Operating Principle

In normal operation the electric actuator opens and closes the valve and, in doing so, winds up a helical compression spring inside a fully sealed canister. A rack and pinion gear transfers spring force to the valve and a planetary gear set provides a configurable input ratio. The spring is held by a self-locking mechanical hold, so the valve stays where it is commanded without creeping from leaking pistons or temperature swings.

When a trip occurs, an electric linear solenoid release, 24 VDC as standard with passive power consumption below 25 W, frees the mechanical hold and the spring drives the valve to its safe position. Adjustable end stops give plus or minus 5 degrees of travel adjustment, and a damper adjusts the speed of fail-safe operation to avoid hydraulic shock in the line. The spring design does not allow uncontrolled release if the unit is disassembled, which is an important safety feature during maintenance.

Engineering Design of the Limitorque MXFS/QXFS

Because the Limitorque MXFS/QXFS is built on the MXb and QXb platform, it keeps the non-intrusive double-sealed enclosure rated up to IP68, the LimiGard circuit monitor and the built-in self-test of the smart actuators. The spring canister is fully sealed with mechanical seals at ingress points and double seals at dynamic interfaces, and the unit has an IP68 rating as standard. Indication can be provided by a switch box or by a NAMUR mounting for standard position feedback, and an optional integrated high-low pressure pilot supports line-pressure triggered emergency shutdown.

On the Limitorque MXFS/QXFS a standard mechanical anti-back-drive device protects the actuator and prevents leakage, and the modular, scalable design allows the torque range to scale from 1,290 in-lb (146 Nm) to more than 1,720,000 in-lb (194,480 Nm). Network options of the MXb actuator include Modbus, Profibus DP with RedCom, Foundation Fieldbus H1, Profibus PA, DeviceNet and HART, and the actuators are compatible with the manufacturer RedRaven monitoring platform and the FlowSync app for configuration over Bluetooth.

Key Features

These characteristics are why engineers choose the Limitorque MXFS/QXFS for critical shut-off duty:

• True mechanical fail-safe action with fail-open or fail-closed options and no dependence on stored hydraulic or pneumatic energy.
• No tubing, fittings or hydraulic fluid to inspect, which removes leak paths and the associated maintenance and audit work.
• Low energy consumption and a zero-emission design, which the manufacturer links to a lower carbon footprint than pneumatic alternatives.
• SIL 3 capable design with a release solenoid and optional high-low pressure pilot for emergency shutdown.
• Full MXb and QXb capabilities, including network communication, remote diagnostics, RedRaven and FlowSync.
• Spare parts that are consistent with the MX and QX product line, which simplifies stores for sites that already use Limitorque electric actuators.
• A scalable torque range from 146 Nm to more than 194,000 Nm for small ball valves through to large pipeline valves.
• Four standard and four optional status and alarm contacts, analogue position or torque feedback and inputs for ESD, partial stroke test, inhibit and lockouts.

Industrial Applications

For gas gathering, pipeline block valves, compressor station isolation and wellhead safety valves in Oman, the Limitorque MXFS/QXFS offers a self-contained fail-safe package that can be installed where no instrument air header or hydraulic power unit exists. The electric operation of the Limitorque MXFS/QXFS suits solar-powered and remote sites, and the sealed IP68 enclosure copes with coastal salt, sand and heat. Operators who currently use spring-return pneumatic units such as the Biffi ALGAS spring-return pneumatic actuator or hydraulic units such as the Biffi OLGAS-H fail-safe hydraulic actuator can compare maintenance, emissions and signal integration with the electric option.

Power plants and refineries in Sohar, Duqm and Salalah can use the actuator on fuel-gas shut-off and burner-management valves, and where pneumatic ESD valves are tested with a positioner such as the Masoneilan SVI II ESD digital valve positioner, the Limitorque MXFS/QXFS offers inputs for partial stroke testing on the electric actuator itself. Seven Star LLC can help engineering teams review the safety function of the Limitorque MXFS/QXFS, the required response time and the proof-test interval against the documentation supplied by the manufacturer.

Technical Specifications

Values are taken from the manufacturer brochure and product page; final ratings depend on the selected MXb or QXb base actuator and gearing.

Request a Quote for Limitorque MXFS/QXFS

To receive a quotation for the Limitorque MXFS/QXFS, send Seven Star LLC the valve type, break and running torque, fail-safe direction, required closing time and signal scheme. We can supply the official brochure, review the options with you and confirm lead time for Oman and the GCC. Contact our instrumentation team to discuss ESD logic, spare parts and commissioning support for every Limitorque MXFS/QXFS in your project.