Flowserve Limitorque SMB Multi-Turn Electric Actuator

Limitorque SMB multi-turn electric actuator: what the SMB designation covers

The SMB is the heavy-duty, intrusive multi-turn electric actuator in the Flowserve Limitorque range. It is built around a cast or ductile iron housing and a double-reduction gear train, and it is aimed at valves that need very high torque and thrust and a very long service life. Seven Star LLC supplies SMB actuators in Oman and the GCC as an independent supplier in Muscat. Because the SMB is a family and not a single part, the exact size, gearing, motor and options must be fixed from your valve data before an order.

How to read the name: the digits after SMB give the frame size, running from the small SMB-000 and SMB-00 up through SMB-0 to SMB-5. The suffix T on the SMB-5T means a torque-only version without thrust bearings, so the valve yoke must carry the thrust. The SB and SBD variants add a spring-compensated stem nut to the same frame. The maker quotes a service life often beyond 30 years for the range.

SMB technical specifications

Explosion-proof, Navy and nuclear constructions exist for this family. For XP builds the maker lists Factory Mutual Class I Groups C and D Division 1 and Class II Groups E, F and G, and CSA Class I Groups C and D Division 1. Any approval has to be confirmed against the nameplate of the exact unit ordered.

How the SMB works: gearing, hammer-blow and torque limiting

The motor drives a worm and helical gear set that turns a drive sleeve and stem nut. Two features set the SMB apart from simpler actuators. The first is the hammer-blow action: the motor is allowed to reach full speed before the load is picked up, so there is momentum available to break a stuck valve free from its seat. The second is automatic torque limiting: when an obstruction is met, a torque switch de-energizes the motor before the valve parts are overstressed.

A geared limit switch tracks travel in both directions and also drives the open and closed indication. Switches and terminals sit in a compartment that is easy to reach during commissioning. A handwheel is always present, and the motor disengages when the handwheel is used; the actuator can be declutched for manual operation at any time, which matters during a power failure. An insertable stem nut allows the actuator to be moved to another valve without major stripping.

SMB sizes: torque, thrust and weight by frame

The table gives the maximum commercial-service ratings per frame. Maximum torque depends on output speed, and the figures apply to the largest motor for each size.

Stem capacity grows with the frame. The SMB-000 accepts a threaded stem to 1.375 in in the two-piece nut design, the SMB-3 to 5 in, and the SMB-5 to 6.25 in; bored and keyed one-piece drive sleeves take larger diameters, up to 10 in on the SMB-5XT. Check the valve stem diameter and thread against the sleeve data before choosing a frame.

SB and SBD spring-compensated versions

For valves where heat or speed causes trouble, the maker offers spring-loaded stem nuts. The SB (single-compensating) lets the stem nut float upward so that thermal expansion of a hot valve stem does not jam the valve and so that seating shock from fast-closing gate or globe valves is absorbed. This allows operation at up to about three times normal speed. The SBD (double-compensating) floats both ways, which suits stem contraction and torque back-seating duty. SB and SBD share torque and thrust ratings, gear ratios, electrical options and mounting bases with the SMB of the same size, so they are interchangeable with the matching SMB frame if valve conditions change.

Where the SMB fits: valves, gearboxes and related actuators

An SMB mounts directly on rising-stem gate and globe valves. For butterfly, ball and plug valves it is combined with a quarter-turn gearbox such as the HBC or WG types, and the V and SR gearboxes serve multi-turn duty. In the same Flowserve Limitorque electric range you will find the LQI and QX quarter-turn actuators and the MXa non-intrusive multi-turn unit, which are the usual alternatives when an intrusive iron-housed actuator is not required.

Selection and ordering checklist for the SMB

• Valve type, stem diameter, thread or key dimensions, and rising or non-rising stem.
• Required seating and running torque and the maximum thrust, including any back-seating demand.
• Valve stroke time or required output speed in rpm.
• Supply: voltage, phase and frequency (60 Hz or 50 Hz), and available motor ft-lb size with 2-pole or 4-pole speed.
• Hazardous area class, ambient range, and whether weatherproof, explosion-proof or nuclear construction applies.
• Control scope: no controls or integral reversing controls, position transmitter, local control station and dial indicator.
• Need for SB or SBD spring compensation or a handwheel spur.

Installation, commissioning and maintenance of the SMB

Check the mounting flange against the base table for the frame, since pilot diameter and bolt circle differ for each size. Fit the drive sleeve to the valve stem, set the geared limit switch and torque switch to the valve’s travel and rating, and confirm motor rotation before connecting to the plant control system. Breathers, drains and a heater in the compartment limit condensation, which is useful in humid coastal sites. Routine care is mainly keeping the grease charge to the maker’s schedule, checking the wiring terminals and the switch compartment for moisture, and operating the handwheel periodically. Installation, operation and maintenance instructions are in the maker’s SMB IOM; ask us for the document reference if you need it.

Typical SMB applications in Oman and the GCC

The brochure lists oil and gas wells, platforms and pipelines, tank farms, refineries, petrochemical plants, power stations, water and wastewater works, dams and steam distribution among its fields of use. In Oman and the Gulf the practical fits are large gate and globe valves on crude and product pipelines, terminal manifold valves, large water transmission valves in desalination and utility networks, and steam isolation duty in power plants. High ambient heat and dust favour the sealed iron housing; check that the standard temperature rating of -29 to 66 °C suits the installation, including solar gain on the actuator body.

Information to send with an RFQ for the SMB

• Existing actuator nameplate data (size, order number, serial number) if this is a replacement.
• Valve manufacturer, type, size, pressure class and stem details.
• Torque and thrust demand, speed and duty cycle.
• Power supply and control voltage, and any remote signals required.
• Area classification and environmental conditions.
• Quantity and required delivery point in Oman or the GCC.

Documents and quotation

The maker’s SMB brochure with the performance and dimension tables is attached on this page. Please use it to shortlist a frame size, then send the valve data above so we can confirm the correct configuration.

Send the SMB model, motor size and your duty details to Seven Star LLC and we will prepare a quotation and confirm lead time for Oman and the GCC.