Compact Pneumatic Cylinder - How to Select the Series for a Machine?
A compact pneumatic cylinder is a suitable choice when a machine requires adequate force within a limited installation length and over a relatively short stroke. Correct selection requires more than checking the piston diameter and stroke. The actual operating pressure, direction of motion, speed, lateral loads, mounting method and operating environment must also be considered.
The SKP series manufactured by CPP PREMA includes cylinders with piston diameters from D16 to D100 in several design variants. Double-acting, single-acting, double-sided piston rod and anti-rotation versions are available. In addition to catalogue products, CPP PREMA manufactures custom cylinders, including units made entirely of acid-resistant steel.
What Is a Compact Pneumatic Cylinder?
A compact pneumatic cylinder is a linear actuator in which compressed air moves a piston and the connected piston rod. Its body is shorter than that of a conventional cylinder with a comparable piston diameter. This compact design reduces the installation length while retaining the force generated by the effective piston area.
The defining feature of a compact cylinder is not simply a small piston diameter. It is the relationship between body length, stroke and available force. A compact cylinder can therefore clamp, lock, eject or provide a short linear movement in a location where an ISO 15552 cylinder would be too long.
CPP PREMA SKP cylinders operate with filtered compressed air, either lubricated or non-lubricated. The maximum operating pressure is 10 bar and the standard temperature range is -20 degrees C to +80 degrees C. The maximum permissible solid particle size in the medium is 10 micrometres. If oil-mist lubrication is introduced into the system, the supply of lubricated air should then be continued.
The standard SKP version has an aluminium-alloy body, end covers and piston. The piston rod and guide rods are made of chrome-plated carbon steel or acid-resistant steel, while the standard seals are polyurethane. The material specification of a custom version must always be verified against the documentation for the specific order.
Detailed versions and available sizes can be found in the SKP compact cylinder range.
Is a Compact Cylinder the Same as a Small Pneumatic Cylinder?
Mini cylinders complying with ISO 6432 usually have a narrow, elongated body. They are suitable for light mechanisms, low loads and installations where width is restricted. SKP compact cylinders have a short block-type body and are selected primarily when the available axial installation length is limited.
| Feature | SKP compact cylinder | ISO 6432 mini cylinder |
|---|---|---|
| Main benefit | Short installation length | Small piston diameter and low mass |
| CPP PREMA piston diameter range | D16-D100 | D12-D25 |
| Body shape | Short block-type body | Narrow round body |
| Typical tasks | Clamping, locking, ejecting and short-stroke movement | Light mechanisms and auxiliary movements |
If the design is constrained by cylinder diameter, consider the ISO 6432 D12-D25 round mini cylinders. If axial body length is the main constraint, the SKP series is the more appropriate starting point.
When Should a Compact Pneumatic Cylinder Be Used?
A compact pneumatic cylinder should be used when the application requires a short, repeatable movement and the designer has limited space along the piston rod axis. Typical examples include clamping a component in an assembly fixture, locking a pallet on a conveyor and ejecting a part from a nest.
Typical compact cylinder applications include:
- clamping and holding workpieces;
- locking mechanisms, slides and pallets;
- ejecting parts from moulds, nests and fixtures;
- closing small flaps and guards;
- positioning parts before assembly or inspection;
- sorting products on conveyors;
- moving stops and auxiliary components;
- retrofitting machines with limited installation length.
A compact cylinder may also be useful in welding fixtures, test stations, packaging machines, assembly systems and simple handling devices. The moving component must be guided correctly, and significant transverse forces must not be transferred directly through the piston rod.
When Is a Compact Cylinder Not the Best Choice?
A compact cylinder is not the best choice when the application requires a long stroke, must withstand substantial lateral loads, involves very high kinetic energy or requires adjustable end cushioning. A short body solves an installation-space problem, but it does not remove limitations related to dynamics and load guidance.
High Lateral Loads and Moments
High lateral loads and moments should be carried by an external guide, bearing arrangement or the machine structure rather than by the cylinder piston rod. Excessive transverse force causes uneven wear of the rod bearing and piston rod seal, increases friction and can lead to leakage.
Long Stroke and High Speed
Long stroke and high speed require the designer to check compressed-air flow, impact energy at the end positions and piston rod rigidity. SKP cylinders with D16-D25 piston diameters have M5 ports, while D32-D100 versions have G1/8 ports. A small port can restrict the dynamics of a large cylinder, so piston diameter alone is not sufficient for selection.
Adjustable End Cushioning
Adjustable end cushioning is not included in the basic compact-cylinder specification defined by ISO 21287. If the moving mass has high kinetic energy, suitable flow control, an external shock absorber, a mechanical stop or another cylinder type designed for the required duty cycle should be used.
What Does ISO 21287 Mean When Selecting a Compact Cylinder?
ISO 21287 for compact cylinder selection specifies basic dimensions for metric-series, single-rod compact cylinders with piston diameters from 20 mm to 100 mm and a maximum operating pressure of 10 bar. Standardisation supports machine design, but it does not mean that every product marked ISO is interchangeable without checking its dimensional drawing.
When selecting a replacement, compare:
- mounting-hole pitch and diameter;
- body length for the specified stroke;
- piston rod end thread and length;
- position and type of pneumatic ports;
- sensor mounting options;
- type of operation and de-energised position;
- mounting accessories and the space required for servicing.
The SKP family covers D16-D100, including versions whose dimensions comply with ISO 21287 and supplementary variants intended for additional functions. D16 is outside the nominal piston diameter range stated in the official scope of the standard. The CPP PREMA catalogue also notes that the D80 body dimensions do not comply with ISO 21287. When replacing a cylinder, use the dimensional drawing for the exact version rather than relying solely on the standard designation.
The scope of the standard can be checked on the ISO 21287 page.
How Do You Select a Compact Pneumatic Cylinder?
Compact pneumatic cylinder selection should begin with the required motion function. Then check the installation space, required force, stroke, dynamics, lateral loads and operating environment. Only after gathering this information should you select the piston diameter and the appropriate SKP series variant.
1. Define the Motion Function
The motion function of a compact cylinder determines whether the actuator must push, pull, operate in both directions, return by spring force or maintain a fixed tool orientation. This function determines whether a single-acting or double-acting version is required and whether the ZT variant should be used.
2. Measure the Available Installation Space
The available installation space for a compact cylinder must include not only the body length but also the extended piston rod, working attachment, tubing, fittings and sensors. Sufficient access must be provided for connecting the pneumatic system and for subsequent removal.
3. Determine the Required Force
The required compact-cylinder force depends on the load, resistance to motion, friction, direction of operation and required dynamics. Selecting with no reserve increases the risk of the cylinder stalling after a pressure drop or an increase in resistance, so an appropriate force margin is required.
4. Select the Piston Diameter
The piston diameter of a compact cylinder determines the effective area on which pressure acts. A larger piston diameter produces more force, but it also increases body width, air consumption and the required flow rate.
5. Select the Stroke
The stroke of a compact cylinder should match the actual mechanism travel, including tolerances and the adjustment method. Do not increase the stroke unnecessarily because this affects the overall length, cycle time and stability of the loaded piston rod.
6. Evaluate Dynamics and Load Guidance
The dynamics and load guidance of a compact cylinder determine whether the actuator can stop the moving mass safely and whether the piston rod will be subjected to transverse loading. For fast cycles, check the flow rate, speed control and impact energy. If lateral forces are present, use separate external guidance.
7. Check the Operating Environment
The operating environment of a compact cylinder affects the material specification, seals and scope of any custom design. Define the temperature, humidity, dust exposure, presence of chemicals, washdown frequency and any requirements for potentially explosive atmospheres.
If piston position monitoring is required, space for sensors and cables must be included. D32 and D40 cylinders have three slots for magnetic field sensors, while D50, D63, D80 and D100 cylinders have seven slots.
Which SKP Compact Cylinder Variant Should You Select?
The SKP compact cylinder variant should be matched to the working direction, return method, required stability and piston rod function. Designations 040-043 apply to D16-D25 piston diameters, while designations 050-053 apply to D32-D100 piston diameters.
| Machine requirement | SKP variant | Operating principle | Key consideration |
|---|---|---|---|
| Controlled motion in both directions | SKP 040/050 | Double-acting, single-sided piston rod | Universal version for moving, clamping and locking |
| Maintaining component orientation | SKP 040/050 ZT | Double-acting with anti-rotation device | ZT does not replace an external guide for high lateral loads |
| Motion or force on both sides of the body | SKP 041/051 | Double-acting, double-sided piston rod | The effective area and force are equal in both directions |
| Working stroke during piston rod extension | SKP 042/052 | Single-acting, pushing version | Return stroke by spring force |
| Working stroke during piston rod retraction | SKP 043/053 | Single-acting, pulling version | The outward return stroke is provided by spring force |
Single-Acting Pneumatic Cylinder
A single-acting pneumatic cylinder is supplied with compressed air for only one direction of motion, while a spring produces the opposite movement. The pushing or pulling version is selected according to the direction in which the working force is required.
Standard strokes for SKP 042/052 cylinders range from 5 mm to 50 mm, while standard strokes for SKP 043/053 cylinders range from 5 mm to 25 mm. This shorter range results from the spring design and from the use of these variants for short clamping, locking and return movements.
Double-Acting Pneumatic Cylinder
A double-acting pneumatic cylinder is powered by compressed air during both piston rod extension and retraction. This design enables motion and speed to be controlled in both directions and is the most common choice for cyclic component movement.
Standard strokes for the SKP 040/041/050/051 variants range from 5 mm to 200 mm. A non-standard stroke can be manufactured after technical consultation, provided that the mechanical conditions and application dynamics permit it.
How Do You Select the Compact Cylinder Piston Diameter for the Required Force?
The compact cylinder piston diameter for the required force is selected on the basis of the actual operating pressure and the effective piston area. The theoretical relationship is expressed by F = p x A, where F is force in newtons, p is pressure in pascals and A is area in square metres.
In practice, use catalogue force values and allow a margin for friction, pressure losses, load variation and movement dynamics. A margin of 20-30% can be a starting point for a straightforward movement, but the final value must reflect the operating conditions of the specific machine.
| Piston diameter | Pushing force at 6 bar | Pulling force at 6 bar |
|---|---|---|
| D16 | 121 N | 91 N |
| D20 | 188 N | 142 N |
| D25 | 295 N | 248 N |
| D32 | 482 N | 415 N |
| D40 | 754 N | 687 N |
| D50 | 1178 N | 1058 N |
| D63 | 1869 N | 1750 N |
| D80 | 3014 N | 2829 N |
| D100 | 4710 N | 4420 N |
D50 Cylinder Selection Example
D50 cylinder selection can be considered when the required pushing force, including the safety margin, does not exceed 1178 N at an actual operating pressure of 6 bar. If the mechanism requires a similar force during retraction, compare the load with the lower pulling force, which is 1058 N for this version.
If the pressure at the operating cylinder falls below 6 bar, the available force also decreases. The pneumatic cylinder force calculator can be used for a preliminary calculation, while the article on how to calculate pneumatic cylinder force explains the calculation method.
When Is an SKP ZT Anti-Rotation Compact Cylinder Required?
An SKP ZT anti-rotation compact cylinder is required when the piston rod end, attached tool or transported component must maintain a defined orientation during extension and retraction. Additional guide rods restrict piston rod rotation about its axis and help maintain the direction of the working movement.
The ZT variant can be used for applications including:
- orienting a component before inspection or assembly;
- guiding a marking punch;
- maintaining the position of a clamping attachment;
- simple handling movements;
- moving a component that must not rotate during the cycle.
The ZT anti-rotation device should not carry high lateral loads or significant moments generated by an extended tool. If the application involves such loads, use an external linear guide or a guided compact cylinder.
Compact Cylinder Made Entirely of Acid-Resistant Steel
A compact cylinder made entirely of acid-resistant steel is a custom solution for environments in which a standard aluminium body or conventional steel components do not provide the required corrosion resistance. CPP PREMA manufactures such cylinders according to the operating conditions and requirements of the specific machine.
In a fully acid-resistant version, all structural metal components of the cylinder, including the body, end covers, piston rod and fasteners, are made of acid-resistant steel. The steel grade, seals, ports, mountings and piston rod end are specified individually. A single steel grade must not be attributed to every custom cylinder unless it has been confirmed in the documentation for that project.
K Option vs Fully Acid-Resistant Version
The K option and the fully acid-resistant version refer to two different material specifications. The catalogue K designation applies to an acid-resistant steel piston rod. A fully acid-resistant cylinder is a custom version that also includes the body, end covers and other agreed metal components.
A version with only an acid-resistant steel piston rod may be sufficient if mainly the extended portion of the actuator is exposed to moisture or a corrosive medium. A complete acid-resistant steel version should be considered if the entire cylinder operates in a humid, aggressive or regularly washed-down environment.
Applications for Acid-Resistant Steel Cylinders
Acid-resistant steel cylinders are used in mining, power generation, the chemical industry, water systems, outdoor machinery and equipment exposed to moisture, salt or aggressive media. Suitability is determined by the complete set of operating conditions, not by the industry name alone.
Acid-Resistant Version vs ATEX Requirements
An acid-resistant version and an ATEX version are not the same requirement. Acid-resistant steel improves material resistance, whereas approval for use in a potentially explosive atmosphere requires the zone, equipment category and documentation scope to be defined for the specific product.
For a mining application, provide information about the presence of methane, coal dust, moisture and corrosive substances, as well as the operating temperature and required equipment category. CPP PREMA solutions for this sector are described on the pneumatic systems for the mining industry page.
What Are CPP PREMA's Manufacturing Capabilities for Compact Cylinders?
CPP PREMA’s manufacturing capabilities for compact cylinders include catalogue SKP products and modifications developed for a specific machine. In-house manufacturing makes it possible to adapt the stroke, materials, piston rod, mounting arrangement and sensor interface to the actual application conditions.
Available modifications include:
- non-standard stroke after technical consultation;
- acid-resistant steel piston rod;
- fully acid-resistant custom design;
- male piston rod thread in the GZ version;
- ZT anti-rotation device;
- custom piston rod end;
- mounting arrangement adapted to an existing machine;
- selection of magnetic field sensors;
- manufacture from a drawing, sample component or measurements;
- replacement for a component no longer available on the market.
Reproducing a Cylinder for a Machine Retrofit
Reproducing a cylinder for a machine retrofit can begin with technical documentation, a catalogue number, photographs, measurements or a supplied sample. The essential requirement is to retain the function, mounting arrangement, stroke and required force without unnecessary changes to the machine structure.
Pre-Delivery Inspection
Pre-delivery inspection of a cylinder should confirm dimensional compliance, leak-tightness and correct operation within the agreed range. For a custom cylinder, the inspection scope should be linked to the project documentation and the customer’s acceptance requirements.
Further information about the production facilities and scope of supply is available on the pneumatic cylinder manufacturing at CPP PREMA page.
Can an SKP Compact Cylinder Be Repaired?
An SKP compact cylinder can be repaired if the condition of its body, piston rod and guiding components permits further operation. Replacing worn seals can reduce downtime costs and retain the existing machine installation without replacing the complete actuator.
A repair kit should be selected using the exact order number, piston diameter, design variant and cylinder version. A similar seal size does not guarantee correct compatibility with another model.
Available components can be found in the repair kits for SKP compact cylinders category. Before overhauling the actuator, determine the cause of leakage. Seal replacement alone will not correct misalignment, lateral overloading or contaminated compressed air.
What Information Is Required for Compact Cylinder Selection?
The information required for compact cylinder selection should describe the task, operating conditions and available space. The more complete the information supplied to the technical team, the lower the risk of oversizing, insufficient force or incompatibility with the existing machine.
Include the following information with the enquiry:
- description of the cylinder function;
- required force and direction of the working stroke;
- actual pressure measured while the machine is operating;
- required piston diameter and stroke;
- maximum length and width of the installation space;
- expected speed and number of cycles;
- mass of the moving component;
- information about lateral forces and moments;
- mounting method and piston rod end;
- sensor type and position;
- temperature, moisture, dust and presence of chemicals;
- acid resistance or ATEX requirements;
- drawing, photograph, catalogue number or physical sample.
If the parameters are unknown, send a description of the problem and the existing installation. The technical team can help identify the information required to select a catalogue version or assess the feasibility of a custom cylinder.
FAQ - Compact Pneumatic Cylinders
This compact pneumatic cylinder FAQ answers common questions about terminology, selection, dimensional compatibility, loads, acid-resistant versions and servicing. The answers apply to the SKP family and to general pneumatic-system design principles.
Do "Pneumatic Piston" and "Pneumatic Cylinder" Mean the Same Thing?
A pneumatic piston and a pneumatic cylinder do not mean the same thing. The piston is a component located inside the cylinder. The cylinder is the complete actuator and includes the body, piston, piston rod, end covers and seals. The expression “pneumatic piston” is sometimes used informally for the entire actuator, but it is not technically precise.
How Does a Compact Cylinder Differ from an ISO 15552 Cylinder?
A compact cylinder differs from an ISO 15552 cylinder</strong> primarily in body length, available port sizes and end-of-stroke cushioning. A compact cylinder is suitable for short installation spaces, while an ISO 15552 cylinder is more commonly selected for longer strokes, higher dynamics and a wider range of accessories.
Is a Compact Cylinder the Same as a Small Pneumatic Cylinder?
A compact cylinder is not always the same as a small pneumatic cylinder. A compact design means a short installation length, while a small cylinder may be a mini cylinder with a small piston diameter. The correct selection depends on whether the design is constrained by length, width, mass or required force.
How Do You Select the Piston Diameter of a Compact Cylinder?
The piston diameter of a compact cylinder is selected according to the required force, actual pressure and direction of motion. In a single-sided piston rod version, the pulling force is lower than the pushing force. Both directions must therefore be checked, with an allowance for losses and load variation.
When Should You Select a Single-Acting Pneumatic Cylinder?
A single-acting pneumatic cylinder should be selected when the working movement is required in only one direction and a spring can provide the return stroke. This solution is suitable for short clamping, locking and return mechanisms, but the available force and the safe position after loss of pressure must be checked.
When Is a Double-Sided Piston Rod Version Required?
A double-sided piston rod version is required when movement or force is needed on both sides of the body or when the same effective area is required in both directions. This function is provided by the SKP 041 and 051 variants.
Does the ZT Anti-Rotation Device Replace a Linear Guide?
The ZT anti-rotation device does not replace a linear guide for high lateral loads and moments. ZT restricts piston rod rotation and helps maintain tool orientation. A linear guide carries forces resulting from mass, eccentricity and the distance between the load and the cylinder body.
Will an ISO 21287 Cylinder Always Fit in Place of Another Brand?
An ISO 21287 cylinder will not always fit automatically in place of another brand. Before replacement, compare the dimensional drawings, stroke, piston rod thread, ports, mountings and sensors. The standard supports selection, but specific variants may differ in design details.
Which Strokes Are Available in the SKP Series?
The SKP series offers standard strokes from 5 mm to 200 mm for variants 040/041/050/051, from 5 mm to 50 mm for variants 042/052 and from 5 mm to 25 mm for variants 043/053. A non-standard stroke can be manufactured after technical consultation and verification of the application conditions.
Does CPP PREMA Manufacture the Entire Cylinder from Acid-Resistant Steel?
CPP PREMA manufactures custom cylinders entirely from acid-resistant steel. In this version, all structural metal components, including the body, end covers, piston rod and fasteners, are made of acid-resistant steel. The material grade, seals, mountings and ports are selected for the conditions of the specific application.
Can an Acid-Resistant Cylinder Be Used in a Mine?
An acid-resistant cylinder can be used in a mine if its design, materials and documentation meet the actual operating conditions. Acid resistance alone does not confirm ATEX compliance, so the zone, equipment category and explosion-risk requirements must be specified separately.
Can CPP PREMA Manufacture a Replacement for a Non-Standard Cylinder?
A replacement for a non-standard cylinder can be manufactured from a drawing, parameters, photographs, measurements or a supplied sample. The function, force, stroke, mounting method, ports, materials and operating conditions must be defined before production.
Can an SKP Cylinder Be Overhauled?
An SKP cylinder can be overhauled if its mechanical components are not permanently damaged. The original repair kit should be selected using the order number and cylinder version, and the cause of seal wear should be identified before repair.
How Do You Select the Correct CPP PREMA Compact Cylinder?
The correct CPP PREMA compact cylinder should provide the required force and stroke, fit within the available installation space and match the application’s dynamics and operating environment. Selection of the SKP 040-053 variant, ZT anti-rotation device, acid-resistant steel piston rod or fully acid-resistant design should follow from the application parameters.
Send the required force, stroke, installation-space dimensions, actual operating pressure and a description of the operating conditions. The CPP PREMA technical team will select a catalogue version or assess the feasibility of a custom cylinder.
Contact CPP PREMA for compact cylinder selection
For basic information about actuator design and other cylinder types, see the article Pneumatic cylinder – operating principle, types and selection.