SMC Locking Cylinders

Stopping a pneumatic cylinder in emergency situations or during regular operations is essential to machine safety. Although there are many ways to solve this challenging application, stopping the flow of compressed air using an air circuit combined with a mechanical locking cylinder will be the most enhanced level of safety.


The energy in compressed air can be controlled and directed by solenoid valves to produce cylinder motion, but it can also be harnessed to abruptly stop cylinder motion.


The common way to stop cylinder motion is to direct the compressed air through a 3-postion, spring return, center closed solenoid valve to trap the pressurized air on both sides of a cylinder in an e-stop situation. When electrical power is interrupted purposefully (e-stop) or accidentally, the spring return function will position the valve back to the center, trapping the pressurized air, thus halting all pneumatic motion.


Although stopping a cylinder with a pneumatic circuit can be highly effective, this method alone is not recommended for maintaining the cylinder in its stopped position, especially when it is bearing a heavy vertical load.


The primary reasons for not solely relying on a 3-position, center closed valve for holding cylinder position:
• Risk of air leaking from the seals of the valve’s outlet ports
• Risk of air leaking from the seals of the valve’s spools
• Risk on the spring force holding the valve in the center closed position
• Risk of cylinder drift caused by the area differential on the piston extend side vs. the retract side
• Risk of air leaks from the overall system (fittings, tubing etc.)

All of these risks can be mitigated by adding a mechanical rod lock to the cylinder.

Locking cylinders come in two types, locking type or end lock of the rod at extension or retraction, and a braking type or fine lock, where the piston rod can stop and maintain a position at mid stroke. Both types of locking mechanisms can be activated by either when air pressure is lost or when air is pressurized.

Some common applications for locking or braking cylinders are:
• Press, clamping or holding a cylinder position for welding, drilling etc.
• Stopping a cylinder to maintain a safety zone during repairs
• Holding a static load
• Drop prevention
• Emergency stop

Note: Installing a pressure regulator and flow controls to balance the air pressure for the circuit to adjust for piston area differential is also recommended when using an end lock or fine lock cylinder. For more on locking cylinders, visit www.smcusa.com.

SMC Locking Cylinders:

SMC CNG Locking Cylinders - Greater locking efficiency as well as stable locking and unlocking operation has been achieved with the CNG cylinder series by arranging a large number of steel ball bearings in circular rows. The floating taper ring provides alignment and stable locking force with respect to piston rod eccentricity. Unlocking pressure of 0.25MPa (0.05MPa lower than conventional SMC product).

SMC CNA2 Locking Cylinders - The CNA2 series cylinder with lock is suitable for mid-stroke stops, emergency stops, and drop prevention. An equal holding force in extending and retracting directions make it possible to lock at either end of the stroke. High reliability and stable holding force are maintained by using a substantially lengthened brake shoe with superior wear resistance. The locking mechanism is isolated from lock release air, so lock function is not diminished by excessive dirt or drain in compressed air.

SMC CNS Locking Cylinders - The CNS series cylinder with lock is ideal for applications requiring intermediate and emergency stop and drop prevention. The compact lock unit saves space and the enclosed construction and separation of the lock mechanism and the unlocking piston chamber minimizes the influences of poor air quality.

SMC CLG1 Locking Cylinders - The series CLG1 is provided with a compact locking mechanism that locks in both directions. The piston rod can be locked in either direction of its cylinder stroke. It is suitable for intermediate stops, for emergency stops, and for drop prevention. The CLG1 fine lock cylinder is part of SMC's CG1 cylinder series.

SMC MLGC Locking Cylinders - The MGC guide cylinder is ideal for material handling applications involving stopping, lifting, and pushing. It combines the functions of a conventional linear cylinder, and a non-rotation device. Features include standard air cushions, grease nipple, and switch capability. Other features include, slide or ball bushing bearings, compact design, adjustable air cushion, and lightweight guided actuator.

SMC CLS Locking Cylinders - The CLS series cylinder with lock is ideal for applications requiring intermediate and emergency stop and drop prevention. The compact lock unit is lightweight and saves space. A switch is optional on the brake cylinder so the operating state of the lock unit (brake piston) can be detected using the switch signal. By separating the lock mechanism and the brake cylinder, SMC has minimized the influences of unlocking air quality such as moisture and condensation.

SMC CLA2 Locking Cylinders - The CLA2 cylinder acts as an air-operated brake with spring-backup. When external position feedback sends a signal to an air valve, the brake is actuated and fast-acting shoes grab the actuator shaft. When pressure is removed, the spring automatically locks the brake onto the shaft. Three locking mechanisms are available: spring lock, air pressure lock and air/spring pressure lock. The CLA2 locks in either direction, comes in five bore sizes, and is available with PT or NPT ports. Other features include non-lube operation, air cushions, and seven mounting styles.

SMC CLJ2 Locking Cylinders - The CLJ2 offers a brake mechanism to stop the position rod at any position while retracting or extending. Choose from three different brake mechanisms to select the unit best suited for your application. Compact and lightweight, the CLJ2 is part of SMC's CJ2 product line.

SMC MWB Locking Cylinders - The MWB series is a tie-rod cylinder MB series with lock and is ideal for applications requiring intermediate stops, emergency stops, and drop prevention.  The MWB series is an improved design over the MNB series with its improved ease of maintenance with separate lock and cylinder construction.  The exhaust locking design allows for the lock release to be manually operated with a hexagon wrench.  The MWB series is available with many standard options including seven mounting types, port thread variations, optional rod boot, air cushion or rubber bumper cushion design, pivot bracket option and rod end bracket options.  Available in bore sizes 32, 40, 50, 63, 80, 100mm.

SMC CLM2 Locking Cylinders - The series CLM2 offers a brake mechanism to stop the piston rod at any position while retracting or extending. With three different brake mechanisms and four bore sizes available, SMC gives you the choice of the best unit for your application. The compact and lightweight CLM2 is a part of the CM2 product line.

SMC CLK2 Locking Cylinders - SMC's CLK2 series is a perfect choice for holding applications in either a clamped or unclamped state.  CLK2 cylinders have a compact lock mechanism which minimizes the extension of the length dimension (2mm shorter), while maintaining the mounting interchangeability with the CLK1 existing product line.  The CLK2 is capable of being locked at any position within the entire stroke.  A dedicated solenoid valve is not required for unlocking, thus reducing the initial costs and replacement of the existing equipment.

SMC CNG Locking Cylinders - Greater locking efficiency as well as stable locking and unlocking operation has been achieved with the CNG cylinder series by arranging a large number of steel ball bearings in circular rows. The floating taper ring provides alignment and stable locking force with respect to piston rod eccentricity. Unlocking pressure of 0.25MPa (0.05MPa lower than conventional SMC product).

SMC Pin Clamp Locking Cylinders - SMC's pin clamp cylinder series C(L)KQG/P was designed with 4 body types for a broad range of installation conditions.  There are 55 types of guide pins available and an optional locking mechanism.  C(L)KQG/P series  has positioning and clamping at one time!  Precision adjustment of clamping height is possible by choosing the with-shim type.  Adjustment range: 0.5 to 3mm.

SMC RLQ Locking Cylinders - Series RLQ was developed to provide the safety of drop prevention, at any point of the stroke, should the air supply be cut off.  The RLQ benefits from additional features such as its own built in air cushion and lock unit, standardized bypass piping and home position holding function. The new series RLQ is the perfect solution for applications which require larger kinetic energy, high stroke repeatability and decreased sound levels. Series RLQ, is currently available in bore sizes of 32, 40, 50 and 63mm, with standard stroke options of between 20 – 100mm, series.

SMC MLGP Locking Cylinders - The MLGP-B/F is a compact body, locking actuator integrated with internal guide shafts to isolate the load bearing from the movement of the actuator's rod and seals. The locking mechanism can be specified for either the extension side (F) or the retraction side (B) of the stroke. The brake spring, locking mechanism will engage when air pressure is lost for drop prevention applications and can be released by reintroducing air pressure or via a manual process. The (L) high precision ball bushing allows for smooth operation that ensures stable travel resistance, suitable for pushing and lifting applications. The (M) carbon steel alloy slide bearing provides lateral stability protecting it from side load impacts, suitable for stopping applications.

SMC C96N Locking Cylinders - The CP96N series is available with a single or double rod in 6 bore sizes from 32 to 100mm.  The air cushion and bumper cushion combination greatly reduces noise at the end of stroke.  High accuracy covers and tie rod nuts improve mounting accuracy and extend the cylinder life.  Increasing the precision of the bushing and piston rod, as well as reducing tolerances, has decreased the deflection of the piston rod.  Standard strokes range from 25 to 800mm.

SMC CP96N Locking Cylinder - The CP96N series is available with a single or double rod in 6 bore sizes from 32 to 100mm.  The air cushion and bumper cushion combination greatly reduces noise at the end of stroke.  High accuracy covers and tie rod nuts improve mounting accuracy and extend the cylinder life.  Increasing the precision of the bushing and piston rod, as well as reducing tolerances, has decreased the deflection of the piston rod.  Standard strokes range from 25 to 800mm.