SMC CY3B25-300Z Magnetically Coupled Rodless Cylinder 25 mm

A sealed rodless cylinder with an external slider

CY3B25-300Z is a basic-type magnetically coupled rodless cylinder from the SMC CY3B series. The piston travels inside a sealed tube and drags an outer slider along with it through magnetic force, so there is no piston rod to seal, and the overall length is little more than the stroke. The cylinder suits long strokes in a small space, such as transferring parts along a track, where a standard rod cylinder would need twice its stroke in free length.

The code reads CY3B (series, basic type), 25 (the 25 mm bore), 300 (the 300 mm stroke) and Z (the suffix used in the standard ordering example of the catalogue). No port-thread letter is given, so the ports are Rc; TN is NPT and TF is G. The catalogue lists 100 to 800 mm as standard strokes for this bore.

Technical specifications

Holding force and vertical use

The magnet holding force of 363 N is the limit of the coupling between the piston and the slider. If the load or the thrust exceeds it, the coupling breaks and the slider slips away from the piston, so the load, the acceleration and the supply pressure must all stay below it. The catalogue also warns of a danger of breaking the magnetic coupling if the cylinder is operated above its maximum operating pressure.

For vertical operation, the catalogue gives an allowable load mass of 18.5 kg at a maximum operating pressure of 0.65 MPa for the 25 mm bore, and recommends guiding the load with a ball-type linear guide; if a slide bearing is used the friction rises and the coupling can be affected. An external stopper is advised for exact positioning, since the slider may drift toward the stroke end under its own weight.

Guiding the load

The CY3B does not carry the load directly. It is guided by an external axis, and the connection bracket must not exceed the maximum weight given in the catalogue, 1.2 kg for the 25 mm size. Self-weight deflection of the long tube must also be considered: the catalogue provides a deflection graph, and the clearance between the cylinder and the mounting surface must be large enough for the full stroke.

The CY3B replaces the older CY1B; if you swap one for the other, confirm the stroke and clearance, because the amount of deflection differs, as the catalogue notes.

Installing the CY3B25-300Z on the machine

Fix the cylinder to a rigid, flat base and align it parallel to the external guide that carries the load. Misalignment between the guide and the cylinder forces the slider sideways, adds friction and works against the magnetic coupling, so check parallelism over the whole 300 mm stroke with the air disconnected by moving the slider by hand. The connection between the slider and the guided carriage should allow small alignment errors to float rather than locking the two parts rigidly together. Keep iron filings, weld spatter and magnetic debris away from the tube and slider, because the magnets inside attract them and they can damage the external surface or the slider wear parts.

Blow out the supply lines before connecting them to the Rc ports, use thread sealant sparingly so that no material enters the cylinder, and fit flow controls so that the piston speed can be set inside the catalogue range.

Commissioning and speed setting

Start with low pressure and flow controls nearly closed, then open them gradually while watching the slider for smooth travel and soft arrival at both rubber bumpers. A rodless cylinder carrying a moving mass stores kinetic energy, and a hard arrival at the stroke end can separate the coupling or shorten the life of the bumpers, so check the moving mass and speed together against the selection pages of the SMC catalogue. For vertical or inclined axes, verify the behaviour when air is exhausted, for example during an emergency stop, and add the external stopper or holding arrangement the catalogue recommends.

Selection points to confirm

• Total moving mass, including the bracket and the guided carriage, against the holding force and the allowable load data.
• Mounting orientation and whether the axis is horizontal, inclined or vertical.
• Required stroke and the deflection of the tube over its supported length.
• Port thread type for the plant piping standard.

Air quality and operating conditions in Oman

The CY3B is listed for non-lube air, and that makes the condition of the compressed air supply important. In Oman and other GCC sites, high summer temperatures and humid coastal air raise the water load on compressors, so effective drying and filtration upstream of the valve manifold help keep condensate and rust particles out of the tube. Keep the ambient temperature around the cylinder inside the catalogue range; a cylinder mounted beside ovens, sealing jaws or in a sun-exposed outdoor frame can run hotter than the room. Fine dust settling on the outer tube is carried by the slider during each stroke, so wipe the tube surface clean during routine maintenance and check the slider for unusual noise, play or uneven movement, which are early signs of wear. Re-check the guide alignment after any mechanical work on the machine frame.

Documents and quotation

The SMC CY3B catalogue PDF below has the model selection pages, how-to-order, specifications, weights and dimensions. Please confirm bore, stroke, thread and the loading conditions before ordering. More cylinders are listed under Pneumatic Cylinders. Seven Star LLC is an independent supplier and quotes the exact code on request.