ISO standards-based actuators are a cornerstone for most manufacturers of pneumatic control technology and are a popular choice for machine builders across industry sectors. The initial demand for standardised dimensions was driven by the car industry seeking dimensionally interchangeable actuators from alternative suppliers. The space envelopes and mounting interfaces agreed within the standards had to allow for the many different manufacturer's technologies e.g. seals, bearings, piston designs and assembly methods.

Inevitably this approach involves compromises to specific features or performance characteristics but creates a good all-round product suitable for many standard applications. However, certain industries and applications may have a greater need for a specific functionality or feature, like a reduced size envelope or lower mass: features which provide them with advantages in terms of performance or function, for a better end-solution. These types of applications can benefit from the use of non-ISO pneumatic cylinder variants. Here are some quick & easy ISO cylinder standards pointers that will help you confidently source and select the right products for your application, in order to achieve top machine performance and a reliable and robust supply chain.

What are ISO standards?

The International Organisation for Standardisation (ISO) is an independent body which creates common standards agreed by global experts for business use around the world. In the world of pneumatic cylinders, the ISO standards refer to basic mounting and accessories dimensions, which enable the interchangeability of pneumatic cylinders regardless of manufacturer.

Why were ISO standards introduced?

ISO standards lay down a framework for the development of standardised products. There are numerous manufacturers & suppliers of pneumatic cylinders globally. Each one creates their own styles of cylinders, with individual space envelopes and mounting interfaces. This provides a huge variety of cylinder types in the market, all fundamentally doing the same thing – a piston with an output connection is forced up and down a tube by a pressure differential. This variety is beneficial for manufacturers because it enables them to produce differentiated product which may be smaller, faster, stronger – providing customers with drives that suit their particular application. However, selecting non-ISO compliant actuators can mean it is harder to switch between suppliers – for instance to meet different end-users' specification or in cases of obsolescence or breakdown. This could seriously impact on maintenance downtimes or product costs. To solve this problem, ISO standards ensure that pneumatic cylinders and their associated mounting components and accessories adhere to defined basic measurements & sizes: making life easier for both manufacturers and their customers. For example, standardisation reduces time during the machine design process, a significant benefit when you consider that pneumatic cylinders are a very common component within many machinery designs.

Which common ISO standards apply to pneumatic cylinders?

ISO 15552:2018 profile cylinders are one of the most popular cylinder types in industry. The standard outlines key dimensions for manufacturers to follow. It provides basic dimensions for the cylinder, along with bore sizes: in this case from 32mm to 320mm. There are given dimensions for the mounting interface and attachable accessories as well as nominal/recommended stroke lengths.

Additionally, there is detail on the types of mounting options (i.e. trunnion mount), accessories (i.e. clevis bracket) and cushioning method. Due to the extended distance between the nose bearing and piston, this design is generally robust and capable of running with some side loading. With more space available in the front end-cap, there are many options for scraper, seal and bearing variants providing options to cope with different demands or running characteristics.

ISO 6432 sets dimensions for round-line cylinders in diameters of 8mm to 25mm, although frequently ranges are offered by manufacturers into higher diameters up to 80mm or 100mm beyond the defined standard. Lighter weight and with built-in mounting interfaces, round-line cylinders are used in many, less rugged applications.

The ISO 6432 cylinder is a versatile product that is commonly found in simple moving, holding and lifting applications. It uses wear resistant materials, providing a longer service life, and come with a wide variety of options for the best application fit. The multiple mounting options give it added flexibility, making it one of the first picks for customers.

ISO 21287 applies to so-called compact cylinders or short stroke cylinders. Using short pistons and front end-caps they are considerably shorter for the same working stroke than the examples above. ISO compact cylinders are an excellent choice in applications where space is at a premium.

However, this comes with the trade-off: they will not be as robust as the standard profile ISO 15552 cylinders and generally should not be exposed to side loadings. Guided and more robust options are available for applications like stoppers on conveyor systems.

Do ISO standards limit product choice?

The short answer is no – or at least: no, they shouldn't. Though manufacturers must adhere to the dimensions/features provided in the ISO standard, they are able to add further functionality or attributes to the cylinder. Examples of this could be different sealing options to accommodate particularly lower or high temperatures, or clamping/braking units. Another example might be a non-ISO stopper cylinder, based on a standard cylinder but with over-sized piston rod diameter and bearings to absorb large side loadings.

Specifiers and end-users are not restricted to only using ISO standard pneumatic cylinders to solve automation challenges. While standardised products bring many benefits, there are also applications that are not optimally served using ISO standard pneumatic cylinders alone. For example, the continuing pressure to miniaturise within the electronics sector demands ever smaller and more compact pneumatic cylinders. A non-ISO cylinder variant could be much more suited for this type of application.

How do ISO and non-ISO products compare?

It is critical to remember that ISO is about dimensional standardisation and not an indicator of quality or performance. Let’s use the Festo product range to illustrate the point. We have several ranges of ISO 15552 cylinders (DSBC, DSBG and DSBF) complying with the standard, but with additional characteristics which support different industries and their applications. DSBC is the standard workhorse, first out of the bag and with performance and long-life running characteristics for most standard applications. The DSBF, is a specialist variant for the food industry that features increased corrosion protection and FDA-compliant greases and seals. DSBG uses a tie rod construction specified in some automotive projects.

DSNU is our ever-popular ISO 6432 round-line cylinder. This year it has been supplemented with a non-ISO variant the DSNU-S. For production volume efficiencies, it shares barrel and rod material – but the new DSNU-S is a space optimised variant, created for simple, linear movements with relatively small loads. It is up to 40% narrower, lighter and up to 35mm shorter than its DSNU ISO equivalent, making it easy to install in tight spaces. Its compact nature makes the DSNU-S a good choice for industries like electronics & light assembly, where the space footprint reduces year on year. Savings on materials and the latest fully automated production also enable manufacturing cost reductions to be passed on to the user.

No ISO bar

ISO standards play an important role in making pneumatic cylinders interchangeable and giving design engineers and machine builders the freedom to choose. Understanding ISO standards and the benefits of complimentary non-ISO variants is essential for smooth product selection.