How to Select a Pneumatic Clamping Cylinder for an Industrial Process
Pneumatic clamping cylinders are primarily used for holding, clamping and accurately positioning components during manufacturing processes. Selection must take account of the required force, pressure available at the cylinder, stroke, operating mode, system geometry and environmental conditions. CPP PREMA manufactures SDK pressure cylinders in catalogue configurations and as special designs adapted to a specific machine.
Correct selection is not limited to choosing a piston bore. The cylinder must provide sufficient force when the supply pressure temporarily drops, complete the required movement without an unnecessarily long stroke and work with the tooling without excessive side loading of the piston rod. The designer must also determine what should happen if the pneumatic supply is lost.
In the CPP PREMA English catalogue, the SDK family is described as SDK Series – Pressure cylinders. In industrial and search terminology, these products are also referred to as pneumatic clamping cylinders. Both terms in this article refer to the same CPP PREMA SDK product family.
Table of contents
What is a pneumatic clamping cylinder?
A pneumatic clamping cylinder is a linear actuator designed to apply a controlled force to a component within a process. Depending on its design, it can hold a part, press it against a locating surface, set its position, block movement or move it to a defined end position.
Compressed air acts on the piston and causes the piston rod to extend or retract. The available force depends mainly on the active piston area and the pressure in the cylinder chamber. Suitability for a specific operation also depends on the stroke, return method, piston rod diameter, load direction and tooling design.
A clamping cylinder is not simply any short-stroke pneumatic cylinder. Within the CPP PREMA range, the SDK Series forms a separate pressure-cylinder family intended for clamping, holding and positioning operations. Compact cylinders form a different design family. Round pressure cylinders for saw applications are another separate group intended for specialised tasks.
What are pneumatic clamping cylinders used for?
The main function of a pneumatic clamping cylinder is to apply a controlled force to a component located in a machine or production station. This does not always mean conventional workholding in a fixture. In many processes, the cylinder temporarily stabilises a component, establishes its orientation or moves it against a mechanical datum.
Typical applications include:
- holding components during machining – before drilling, milling, cutting or marking,
- clamping during assembly operations – holding parts while they are screwed, bonded, pressed or joined,
- accurate positioning – moving a component against a datum, stop or inspection point,
- blocking movement – stopping a mechanism or a product travelling on a conveyor,
- stabilising a product – limiting movement during packaging, inspection or marking,
- sorting and separating – controlling the position of a stop, latch or diverting component,
- special-purpose machines – providing a short working movement in a mechanism designed for a specific process,
- machine retrofit projects – replacing worn, non-standard or obsolete actuators.
A conventional pneumatic cylinder is best suited to repeatable end-position movement. If the process requires accurate stopping at several intermediate positions, displacement measurement or programmable position control, an additional guide, measurement sensor or different drive technology may be required.
How do you select a pneumatic clamping cylinder?
Start by defining the operation the cylinder must perform. Select the bore and stroke only after the process requirements are known. This avoids choosing a cylinder that produces the required theoretical force under ideal conditions but cannot provide it in the actual pneumatic system or does not fit the available installation space.
1. Define the cylinder function
Determine whether the cylinder must clamp, hold, position, block or move the component. Define the force direction and whether the working movement takes place during piston rod extension or retraction.
2. Determine the required force
The cylinder must overcome process resistance and maintain the component in the required position. The calculation should include mass, friction, machining forces, acceleration, load direction and the geometry of any lever mechanism. If the cylinder acts through an intermediate mechanism, the piston rod force will not necessarily equal the force applied to the component.
3. Check the lowest available pressure
Do not base the calculation only on the compressor setting or main pressure regulator. Use the lowest pressure expected at the cylinder while other consumers are operating. Pressure losses can occur in tubing, fittings, directional valves, filters and flow-control components.
4. Select the stroke
The stroke must release the component, accommodate dimensional tolerances and complete the full movement. It should not be much longer than the process requires. Excessive stroke increases cycle time and air consumption and can make stable guidance of the tooling more difficult.
5. Select the operating mode
Determine whether both directions must be pneumatically controlled or whether a working stroke in one direction with spring return is sufficient. The required system behaviour after loss of pressure must also be established.
6. Check side loads and rotation
The piston rod should primarily transmit axial force. If the tooling is subjected to transverse loading, use an external guide or suitable mechanism. When the working tool must retain a fixed angular orientation, ZT anti-rotation protection may be required.
7. Match materials to the operating environment
Moisture, cleaning agents, dust, elevated temperature and aggressive substances affect the selection of materials, seals and lubricant. A standard aluminium configuration will not be suitable for every environment. CPP PREMA can manufacture a special configuration after analysing the application conditions.
How do you calculate pneumatic clamping cylinder force?
The theoretical pushing force is the product of pressure and the active piston area. For the full piston area, use:
F = p × A
When pressure is expressed in bar and piston bore in millimetres, the equation can be written as:
F [N] = 0.07854 × p [bar] × D² [mm²]
where:
- F – theoretical force in newtons,
- p – pressure in bar,
- D – piston bore in millimetres.
Example: D50 cylinder at 6 bar
F = 0.07854 × 6 × 50² ≈ 1,178 N
A force of 1,178 N is approximately equal to the gravitational force acting on a mass of 120 kg. This does not mean that the cylinder can safely support that mass directly without further engineering calculations. Industrial selection must account for losses, motion dynamics, installation geometry and an appropriate safety factor.
Retraction force is lower for a cylinder with a single-sided piston rod because the piston rod cross-section reduces the active area. In a cylinder with a double-sided piston rod, the active area on both sides is reduced by the rod cross-section, which gives similar forces in both directions. In a single-acting cylinder, part of the generated force may be required to overcome the return spring.
For an initial calculation, use the CPP PREMA Actuator Force Calculator. Additional guidance is available in How to calculate ISO pneumatic actuator force. The SDK Series itself must not be described as ISO 15552 or ISO 6432 unless a specific technical document confirms such compliance.
Theoretical pushing force for bore sizes D16-D100
The values below are calculated for the full piston area. The table supports preliminary bore selection. It does not include friction, pressure losses, return-spring resistance or the influence of piston rod design.
| Piston bore | 4 bar | 5 bar | 6 bar | 7 bar | 8 bar |
|---|---|---|---|---|---|
| D16 | 80 N | 101 N | 121 N | 141 N | 161 N |
| D20 | 126 N | 157 N | 188 N | 220 N | 251 N |
| D25 | 196 N | 245 N | 295 N | 344 N | 393 N |
| D32 | 322 N | 402 N | 483 N | 563 N | 643 N |
| D40 | 503 N | 628 N | 754 N | 880 N | 1,005 N |
| D50 | 785 N | 982 N | 1,178 N | 1,374 N | 1,571 N |
| D63 | 1,247 N | 1,559 N | 1,870 N | 2,182 N | 2,494 N |
| D80 | 2,011 N | 2,513 N | 3,016 N | 3,519 N | 4,021 N |
| D100 | 3,142 N | 3,927 N | 4,712 N | 5,498 N | 6,283 N |
Do not select a bore exactly at the calculated force limit. In a stable application, a reserve of approximately 20-30% may be a useful starting point, but it is not a universal safety factor. A larger reserve may be required for dynamic movement, varying pressure, high friction, lever mechanisms or processes where loss of clamping force can cause a fault or hazard.
How do you select cylinder stroke and installation arrangement?
The cylinder stroke should match the actual travel required to release, approach or clamp the component. Include an allowance for component tolerances, fixture adjustment and wear of the working tool. An excessive stroke allowance should not be used to compensate for design errors.
For SDK variants 030, 032, 130 and 132, the catalogue standard stroke range is 5-100 mm. For single-acting SDK variants 031 and 131, the standard range is 5-50 mm. Other stroke lengths can be manufactured after prior technical consultation.
Check the following during installation design:
- space required for the body and extended piston rod,
- access to the pneumatic ports,
- space for sensor installation and replacement,
- routing space for tubing and fittings,
- force direction relative to the piston rod axis,
- risk of collision between the tooling and machine,
- service access to the cylinder.
The working tool should contact the component as close to the piston rod axis as possible. If the mechanism generates a side force, bending moment or rotation, transfer these loads through an external guide, slide or appropriately designed fixture. Increasing the piston bore does not correct inadequate guidance.
Which CPP PREMA SDK pressure cylinder variant should you select?
Select the SDK variant mainly according to the required operating mode and piston rod configuration. Double-acting operation provides pneumatic control in both directions. Single-acting operation simplifies the circuit when the working movement takes place in one direction and spring return is sufficient.
| Series | Catalogue configuration | Operating mode | Standard stroke | When should you select it? |
|---|---|---|---|---|
| SDK 030/130 | With single-sided double-acting piston rod | Double-acting | 5-100 mm | When pneumatic control of both extension and retraction is required. |
| SDK 031/131 | With single-sided single-acting pushing piston rod | Single-acting, pushing | 5-50 mm | When clamping occurs during extension and the piston can return by spring force. |
| SDK 032/132 | With double-sided double-acting piston rod | Double-acting | 5-100 mm | When similar operating conditions are required in both directions or the mechanism acts on both rod ends. |
| SDK 030/130 ZT | With anti-rotation protection | Double-acting | Depending on configuration | When the working tool must retain a fixed orientation during extension and retraction. |
| SDK 031/131 ZT | Single-acting pushing configuration with anti-rotation protection | Single-acting, pushing | Depending on configuration | When spring-return clamping and a fixed tool orientation are both required. |
Product examples illustrating the differences between variants:
- SDK 131 D32 × 20, single-acting, pushing,
- SDK 132 D50 × 20 with double-sided piston rod,
- SDK 130 ZT D40 × 20, double-acting, with anti-rotation protection,
- SDK 131 ZT D50 × 25, pushing, with anti-rotation protection.
These examples show the construction of individual variants. Select the final order number according to bore, stroke, operating mode, piston rod end and required materials.
Kiedy wybrać siłownik dociskowy z zabezpieczeniem przed obrotem ZT?
Select the ZT configuration when the piston rod tool must retain a defined angular orientation relative to the process component. This is important for shaped tools, punches, markers, stops and other parts where rotation would change the point or direction of force application.
Anti-rotation protection improves repeatability of tool orientation. It should not be treated as a guide capable of carrying unrestricted side loads or high torque. If the tool attached to the extended piston rod is heavy, long or exposed to a transverse force, the designer should provide additional external guidance.
Before selecting ZT, determine:
- the required orientation of the working tool,
- the possible torque,
- the distance between the force application point and the piston rod axis,
- the mass and length of the tooling,
- the operating frequency,
- whether an external guide is required.
CPP PREMA SDK pressure cylinders in special designs
CPP PREMA manufactures special pressure cylinders adapted to the conditions of a specific machine and process. A special design is useful when a catalogue product does not match the available space, material requirements, temperature, mounting arrangement or the construction of a retrofitted machine.
Full stainless-steel design
CPP PREMA can manufacture the complete pressure cylinder in stainless steel as an individually engineered product. This solution can be considered for wet or corrosive environments and equipment subject to frequent cleaning. Selection of the steel grade, seals and remaining components requires information about operating temperature, cleaning agents and substances present in the environment.
A full stainless-steel cylinder must not be confused with catalogue designation K. According to the SDK order-number construction, K means an acid-resistant steel piston rod. A complete stainless-steel cylinder is a separate special design agreed individually with CPP PREMA.
Special FKM/Viton seals
CPP PREMA can manufacture cylinders with specially selected seals, including FKM/Viton. This material may be considered for elevated temperature or demanding environments, but the seal material alone does not define the permissible temperature of the complete cylinder. The lubricant, sensors, guides and all other materials must also be assessed.
The working-temperature range must therefore be confirmed for the complete special configuration. Include the normal and maximum temperature, exposure time, medium and cleaning agents in the technical enquiry.
Non-standard stroke and piston rod configuration
If the catalogue stroke does not match the machine geometry, another stroke length can be manufactured after prior technical consultation. The piston rod end can also be adapted. The standard ordering system includes an internal thread, while the GZ designation identifies a piston rod with male thread.
Replacement cylinder for a machine retrofit
Original cylinders in older machines may be obsolete, and their installation dimensions may not correspond to current catalogue series. The starting data should include installation dimensions, stroke, bore, port positions, piston rod end and operating mode. A nameplate photograph, drawing or measurements of the existing cylinder help CPP PREMA assess whether a replacement can be manufactured.
Standard technical specifications of CPP PREMA SDK pressure cylinders
SDK Series pressure cylinders in bore sizes D16-D100 are manufactured in several configurations. The maximum operating pressure of the standard series is 10 bar. The standard working-temperature range with polyurethane seals is -20°C to +80°C.
- Medium: compressed air, filtered, lubricated or non-lubricated.
- Bore sizes: D16, D20, D25, D32, D40, D50, D63, D80 and D100.
- Body, covers and piston: aluminium alloy in the standard design.
- Piston rod and guides: chrome-plated carbon steel or acid-resistant steel, depending on the configuration.
- Standard sealing: polyurethane.
- Options: cylinder with magnet, GZ piston rod with male thread, K acid-resistant steel piston rod and ZT anti-rotation protection.
If oil-mist lubricated air is introduced, the supply of lubricated air should be continued. Correct compressed-air preparation reduces seal wear and the risk of contamination reaching the working surfaces.
Pneumatic clamping cylinders and process safety
Pneumatic force depends on the available pressure. If pressure drops, the clamping force can decrease. If the supply is lost, the force can disappear completely or a single-acting piston may return under spring force. A pneumatic clamping cylinder must not automatically be treated as a mechanical safety lock.
If releasing the component can endanger a person, damage the machine or allow a heavy load to fall, define the safeguarding method from the risk assessment of the complete machine. Depending on the application, a mechanical lock, safety valve, pressure monitoring, position confirmation or another technical measure may be required.
Common pneumatic clamping cylinder selection mistakes
Selecting only by piston bore
Two applications using a D50 cylinder can require completely different strokes, piston rod configurations and operating modes. Bore indicates potential force but does not confirm that the design is suitable for the process.
Using the main regulator pressure in the calculatio
If pressure losses occur, the pressure at the cylinder can be lower than the value measured elsewhere in the installation. Perform the calculation using the lowest pressure expected during the machine cycle.
No force reserve
Selecting a bore exactly at the theoretical limit means that a small increase in friction or drop in pressure can interrupt the process. Match the force reserve to the motion dynamics and consequences of losing the clamp.
Excessive stroke
An unnecessarily long stroke increases movement time and air consumption. It can also make an extended piston rod more susceptible to side loading.
Transmitting side loads through the piston rod
The piston rod should operate axially. Misalignment increases wear of the seals and guides. Tooling that requires guided movement should have its own external guide.
No anti-rotation protection
If the tool has a defined shape or orientation, uncontrolled rotation can change the force application point. Consider the ZT configuration in this situation.
Confusing designation K with a full stainless-steel cylinder
Designation K refers to an acid-resistant steel piston rod. A cylinder manufactured entirely from stainless steel is an individually agreed special design.
Ignoring the consequences of pressure loss
The designer must determine whether the component can be released after loss of supply or must remain securely held. This is particularly important for safety-related applications and retained loads.
Servicing and repair kits
Replaceable sealing components extend cylinder service life and support planned maintenance. CPP PREMA supplies repair kits for SDK Series cylinders for selected bore sizes and variants.
Read the complete cylinder designation before ordering a repair kit. Bore alone may not be sufficient because single-acting and double-acting variants use different component configurations. During servicing, also inspect the piston rod and guide surfaces. Replacing only the seals will not remove the cause of failure if the piston rod is damaged or subjected to side loading.
Which data should you provide for cylinder selection or quotation?
The more accurately the process is described, the easier it is to select the correct catalogue variant or prepare a special design. The initial enquiry does not need a complete manufacturing drawing. Basic requirements and materials showing the installation space are sufficient to start the technical assessment.
Include the following information:
- description of the operation performed by the cylinder,
- required clamping force,
- minimum and nominal system pressure,
- expected bore and stroke if already defined,
- working stroke direction,
- single-acting or double-acting operation,
- mounting position and method,
- operating frequency and clamping time,
- normal and maximum operating temperature,
- presence of moisture, dust, cleaning agents or aggressive substances,
- required materials and seal type,
- piston rod thread type,
- requirement for ZT anti-rotation protection,
- position sensing method,
- drawing, 3D model, photographs or dimensions of the existing cylinder,
- required quantity.
For retrofit projects, photographs of the nameplate, body, pneumatic ports and piston rod end are particularly useful. Include installation dimensions in both the retracted and extended positions.
Frequently asked questions about pneumatic clamping cylinders
How do you select the bore of a pneumatic clamping cylinder?
Select the bore from the required force and the lowest pressure available at the cylinder. Reduce the theoretical result by the expected losses and apply a force reserve appropriate to the process. Then verify installation dimensions, stroke, operating mode and piston rod configuration.
How much force does a pneumatic clamping cylinder produce at 6 bar?
Force depends on the piston bore. At 6 bar, the theoretical pushing force is approximately 121 N for D16, 754 N for D40, 1,178 N for D50 and 4,712 N for D100. These values use the full piston area and exclude friction, pressure losses and piston rod design.
When should you select a single-acting pressure cylinder?
A single-acting variant is suitable when the working movement occurs only during extension and spring return is acceptable. This simplifies the pneumatic circuit, but the available force must be checked after allowing for spring resistance. The machine behaviour after pressure loss must also be assessed.
When is a double-acting pressure cylinder preferable?
Select a double-acting cylinder when extension and retraction must both be pneumatically controlled. This provides controlled movement in both directions and helps overcome resistance during return. It requires a suitable directional valve and pneumatic connections to both cylinder chambers.
What is ZT anti-rotation protection used for?
The ZT configuration protects the piston rod against unwanted rotation. It is used when a punch, marker, shaped tool or other working element must maintain a fixed orientation. ZT does not replace an external guide in applications with high side loads or torque.
Can an SDK pressure cylinder be ordered with a non-standard stroke?
Yes. Other stroke lengths can be manufactured after prior technical consultation. Before manufacture, the installation dimensions, piston rod load, expected number of cycles and space for guidance must be checked. A non-standard stroke should be treated as an individually agreed configuration.
Can CPP PREMA manufacture a complete SDK pressure cylinder from stainless steel?
Yes. CPP PREMA can manufacture a complete pressure cylinder from stainless steel as an individual special design. The steel grade, seals and remaining components are selected for the operating conditions. Include information about moisture, temperature, cleaning agents and substances present in the environment.
What does designation K mean for an SDK cylinder?
In the SDK catalogue order-number construction, K means an acid-resistant steel piston rod. It does not mean that the complete cylinder is manufactured from stainless steel. A full stainless-steel design is a separate special product agreed with CPP PREMA.
Can CPP PREMA SDK pressure cylinders use FKM/Viton seals?
Yes. CPP PREMA can prepare special configurations with FKM/Viton seals. The permissible temperature of the complete cylinder must not be determined solely from the seal material. Confirm the operating range for the complete configuration, including the lubricant, sensors and guide materials.
Which information is required for a special pressure cylinder design?
The essential data includes the operation, required force, pressure, stroke, operating mode, mounting position, cycle frequency, temperature, environment and required materials. For a retrofit, include photographs, a drawing and the dimensions of the existing cylinder and installation space.
Pneumatic clamping cylinder selection - key step
The selection process can be organised into five stages:
- Define whether the cylinder must hold, clamp, position or block the component.
- Calculate the required force using the lowest pressure expected at the cylinder.
- Select the bore, stroke and installation arrangement with an appropriate reserve.
- Select single-acting or double-acting operation, piston rod configuration and ZT anti-rotation protection if required.
- Define the materials, seals and special-design requirements.
Standard CPP PREMA SDK pressure cylinders cover bore sizes D16-D100 and several operating configurations. If the application requires a non-standard stroke, special seals, a K acid-resistant steel piston rod or a complete stainless-steel cylinder, the configuration can be agreed individually.
Prepare a description of the operation, required parameters and a drawing or photograph of the installation space before requesting selection support. This allows CPP PREMA to determine whether a catalogue variant or an application-specific special design is the better solution.