Flowserve Limitorque QX Smart Quarter-Turn Electric Actuator

Limitorque QX smart quarter-turn electric actuator: what it is

The QX is the non-intrusive smart quarter-turn electric actuator from Flowserve Limitorque. It carries the technology of the multi-turn MX into a 90 degree package, so you get an absolute position encoder, an on-board motor controller, a graphical display and diagnostic functions in one double-sealed enclosure. Seven Star LLC supplies QX actuators in Oman and the GCC as an independent supplier in Muscat. The QX is a five-frame family, QX-1 to QX-5, and the frame, voltage, communication card and approvals are specified per order.

Non-intrusive means that commissioning is done through magnetic Hall-effect knobs and the LCD, without taking covers off or using special tools. That is helpful in dusty, humid or classified areas, where opening an enclosure is something you want to avoid.

QX technical specifications

How the QX works

The QX motor control board replaces the contactor and reversing starter of conventional actuators. A brushless DC motor drives gearing and a hardened alloy steel worm and worm gear, and the output goes to the valve through a drive bushing or torque nut. Torque is sensed from motor current and compensated for supply voltage and temperature, which removes the springs, cams and switches of older designs. The absolute encoder tracks the valve even when power is lost and the handwheel is turned, since a declutch lever moves the drive to manual and returns to motor drive automatically when the motor is energized.

LimiGard monitors the motor controller, internal logic and external commands against reference conditions and takes over the actuator response on a fault, signaling an alarm. The built-in self-test lets the redundant encoder keep working until a number of faults accumulate.

QX frame sizes, torque and flange options

The brochure lists these ratings per frame. The seating torque of a given unit may also be limited by the mounting base: the 05 base is limited to 100 ft-lb, the 07 base to 200 ft-lb, the 10 base to 400 ft-lb and the 12 base to 1,000 ft-lb.

Handwheel turns for 90 degrees are 50 on QX-1 and QX-2 and 70 on QX-3 to QX-5. Minimum operating times are affected by temperatures below -10 °C.

Control, communication and diagnostics on the QX

Remote control can be four-wire, two-wire, three-wire maintained or three-wire inching. Three modes (discrete, analog and network) can be enabled at once, and the actuator follows the last command it receives. Up to three external ESD signals can drive the valve to a user-defined position, and inhibit inputs can block opening or closing. A monitor relay reports availability for remote operation, and latched S-contacts give position or status. The modulating option accepts a 4-20 mA command and supports proportional band, dead band, polarity and loss-of-signal action as settings. Diagnostic screens show motor and hardware identification, torque profiles and log reports; a Bluetooth option is also mentioned.

Where the QX fits and related Limitorque actuators

For multi-turn valves use the Limitorque MXa, which is the non-intrusive multi-turn sibling; for simpler quarter-turn work without a smart controller see the LQI compact actuator. The heavy iron SMB suits rising-stem valves. The QX is the choice when you need fieldbus integration, torque trending, a precise absolute position output and local display on ball, butterfly and plug valves, or on dampers.

Selection and ordering checklist for the QX

• Valve torque at full differential pressure, plus safety margin, to pick QX-1 to QX-5.
• Valve flange (ISO 5210 or MSS SP-102 style) and stem or shaft bore and key.
• Required operating time per 90 degrees within the frame range.
• Supply voltage, phase and frequency, and control voltage.
• On-off or modulating duty; starts per hour expected.
• Network: Modbus, Foundation Fieldbus, Profibus or DeviceNet, or hard-wired only.
• Position or torque transmitter needs and number of alarm contacts.
• Area classification, ambient limits and any need for special lubricant or paint.

Installation, commissioning and maintenance of the QX

Mount the unit on the valve with the proper base and torque nut, then wire through the separate terminal chamber, which keeps the controls sealed from the site wiring. Configure by answering yes or no questions on the LCD with the two knobs; the setup walks you through travel limits, torque settings and control mode. Gears run in a synthetic oil bath and the brochure describes the design as long-life, so routine care is mainly checking enclosure seals, conduit glands, fasteners and the stored diagnostics and logs. In coastal sites, keep conduit entries sealed and use the coating and stainless fastener features as designed.

Typical QX applications in Oman and the GCC

Locally the QX fits the smart-actuation role on pipeline and terminal ball valves, butterfly valves on cooling water and seawater circuits, emergency shutdown and process isolation in oil and gas, and valves in power and desalination plants that report to a DCS over fieldbus. Wide input voltage tolerance helps where supply quality varies, and the sealed non-intrusive housing is well suited to heat, dust and humid coastal air.

Information to send with an RFQ for the QX

• Valve type, size and maximum torque, with flange and drive dimensions.
• Supply voltage and phase, plus required operating time.
• On-off or modulating, and the control signal or fieldbus type.
• Hazardous area class and temperature range.
• Existing actuator nameplate if replacing a unit.
• Quantity and delivery location.

Documents and quotation

The maker’s QX brochure with the rating tables, options and certifications is attached on this page. Please review it, then send us the frame and options you need.

Send the QX frame, voltage and network type to Seven Star LLC and we will prepare a quotation for Oman and the GCC.