Ordering a replacement pneumatic cylinder: what bore and stroke leave out
Match the mounting, rod end, air connections and position feedback to the existing mechanism.
Imagine a packaging machine waiting for a replacement cylinder. The purchasing note says “32 mm bore, 100 mm stroke.” A proposed unit looks close in the catalog, but the existing rod-end fitting cannot be transferred and the position switch has nowhere to mount. This hypothetical example illustrates what remains unresolved when an inquiry contains only two dimensions. The useful starting point is the movement the cylinder performs and the components it connects to.
Follow the movement before searching for a model
Record the complete model, including suffixes, and photograph the label, both mounting ends, rod-end connection, tubing and switches. An equipment parts list can help identify special options or separately supplied brackets. Collect the information under the equipment’s safe inspection procedure; obtaining a photograph is no reason to move a mechanism or disconnect a pressurized line.
Describe the job in an ordinary sentence: pushing a pack, pulling a slide or holding a workpiece. Confirm the original action and arrangement, such as single or double acting and single or double rod. “Equivalent cylinder” gives a supplier little basis for deciding what must stay the same. Leave unknown fields open and say which photographs or equipment records need interpretation rather than guessing a code.
Treat the body mounting and rod end as one interface
A matching body bracket does not establish the rod-end thread, clevis or pin position. Compare where the connected part sits at full retraction and extension, as well as the cylinder outline. Record dimensions measured on a worn item as observations, separately from nominal dimensions recovered from an approved drawing.
SMC’s CJ2 information lists mounting and switch-mounting variants. [2] For the inquiry, state whether existing brackets must be retained or may be replaced as a set. A proposal that turns a pivoting connection into a fixed mounting changes the mechanism, even if it solves a hole-pattern problem. It belongs in a separate engineering comparison.
- 1Body mounting and fixing position
- 2Rod-end connection and travel envelope
- 3Air ports and position switch
Illustrative schematic. Numbers identify areas to check, not actual port numbers. No dimensions, loads, internal design or interchangeability are specified.
Look at how the load moves and stops
For the same bore, the available pressure area differs between extension and retraction on a single-rod cylinder. Supply the load, orientation, working pressure and required speed. SMC’s selection guide considers load conditions and cushioning energy as well as force. [1] A theoretical catalog force is not, on its own, evidence that the installed task can be performed.
In the packaging example, describe the item moved, direction, end-stop arrangement and existing speed control. External guides, side loads and machine stops also matter. Ask whether the candidate works under the recorded operating conditions or requires a mechanism change. Do not make higher pressure or speed after installation an unexamined assumption in a replacement quote.
Define what comes with the position switch
A quotation saying “with switch” does not establish that the existing detector can be reused. Consider the cylinder magnet, switch, bracket, sensing position, wiring and connector together. SMC’s CG3 ordering example distinguishes the built-in magnet from the specified switch. [3] That family’s notation is not a decoder for every cylinder series.
For the air connection, check port thread, location and surrounding access with the fitting installed. The existing tube should connect without forced routing. A lit switch indicator and the correct input reaching the controller at the intended position are separate checks. Keep detailed output-circuit selection in the sensor discussion; here, make reuse and supplied scope explicit.
Read the unanswered fields in a quotation
The following hypothetical comparison has two candidates. Both match bore and stroke; B includes brackets and switches. Neither has yet answered the duty question. More accessories do not establish suitability, so B cannot be accepted merely because its offer looks more complete.
Turn each unanswered field into a specific evidence request. A dimensioned drawing checks mounting positions, an order code defines supplied options, and a selection response addresses load and motion. Those answers may come from different documents. Retaining their relationship to the purchase requirement makes the final order easier to verify.
| Check | Supplier response | Next evidence |
|---|---|---|
| Bore and stroke | Supplier responseA and B match | Next evidenceConfirm action and both end positions on drawings. |
| Mounting and rod end | Supplier responseA is silent; B includes brackets | Next evidenceDefine reused parts and installed positions. |
| Position feedback | Supplier responseB includes switches | Next evidenceCompare model, mounting, wiring and sensing position. |
| Load and stopping | Supplier responseNeither has answered | Next evidenceProvide pressure, speed, load direction and stop conditions. |
Separate a replacement from a mechanism change
Request an option that retains existing brackets, tubing and control, separately from an alternative involving changes. For a changed arrangement, ask for the differences, additional parts, adjustment work, verification responsibilities and acceptance approach. Otherwise a short cylinder lead time can conceal machining and commissioning work at the machine.
Before ordering, consolidate item identity, installed interfaces, included parts, duty and unresolved conditions. After installation, follow the equipment procedure to verify movement, clearance, stopping and signals in stages. Photos and the conditions already known can support a useful first discussion even when the complete original model has not yet been established.
Questions to adapt for a cylinder inquiry
Open supplier questions
We need a replacement for [complete model] in [equipment/application]. Attached are photos and available dimensions. Bore [ ], stroke [ ], action [ ], working pressure [ ], load and direction [ ], speed/stopping conditions [ ]. We would like to retain [brackets/rod-end fitting/tubing/switch]. Unknown items are [ ]. Please identify differences in mounting, rod end, ports and position feedback, and distinguish included from separate parts. Quote alternatives requiring changes separately, with the work and checks involved. Quantity [ ], required date [ ], destination [ ].
Sources and reading scope
- SMC — Air Cylinders Model Selection
Read selection overview, load/pressure examples and cushion-energy sections. No tabulated value or load factor is prescribed for other products.
- SMC — CJ2/CDJ2-Z web catalog
Read CJ2 mounting, switch mounting and bracket supply notes. This does not establish the supplied scope of every series.
- SMC — CG3 Air Cylinder catalog
Read the CG3 order structure and magnet/switch distinction. Codes and compatible switches are not extended to other families.