The National Fluid Power Association (NFPA) and International Organization for Standardization (ISO) were set up to help alleviate these complexities for machine builders and end users. NFPA is used primarily in North American markets to cover inch products, whereas ISO encompasses the global metric market. The interchangeability that NFPA and ISO standards provide, bring consistency to machine design, simplify maintenance and reduce overall downtime.
NFPA and ISO standards define a variety of features such as mounting styles and overall dimensions, allowing pneumatic cylinders to be interchangeable across different manufacturers.
ISO 21287 applies to compact cylinders or short stroke cylinders. Using short pistons and end-caps, they are considerably shorter for the same working stroke than typical pneumatic cylinders. 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 other standard cylinders and generally should not be exposed to side loadings.
ISO 15552 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.
The NFPA standard (T3.6.x) for square-head pneumatic cylinders is similar in concept to ISO 15552, but with Inch dimensions for cylinder bore sizes from 1.5” to 14”. It defines uniform mounting dimensions for the cylinder as well as the mounting components, so they are dimensionally interchangeable and ensuring compatibility and consistency across manufacturers.
The NFPA interchange cylinders are often manufactured with machined aluminum end caps, providing flexibility with the configuration options such as selecting the air port thread size and the location of the air ports and air cushion adjustment screws. The machined end caps also enable special modifications to meet the unique requirements for many different applications.
Whether you are a small machine builder, global OEM or end user, utilizing interchangeable cylinders can bring consistency to your machine design, simplify maintenance and reduce overall downtime. If you’re interested in a deeper understanding of interchangeable cylinders, download the overview guide.