Non-repairable Air Cylinders

Non-repairable air cylinders, also commonly known as throw-away air cylinders, are a family of lower cost air cylinders that are usually manufactured with aluminum end caps and with a stainless steel tube for a cylinder barrel.

The end caps of the non-repairable air cylinder can be made of cast of aluminum, with minimal machining involved in the process, thus keeping the manufacturing cost low.

Some non-repairable air cylinders have machined plastic end caps. I expect it won't be too long before these plastic end caps will be made by the 3D printing process, possibly reducing cylinder cost even more.

Non-repairable Air Cylinders Assembly

Each end cap has a groove cut around the circumference. After insertion of the piston and rod assembly into the cylinder barrel, the end caps are inserted into the stainless steel tube barrel material so that the grooves in the end caps are inside the circumference of the barrel.

The stainless barrel material is then roll-formed into the groove in the end caps to finish the cylinder assembly.

This is a faster and lower cost cylinder manufacturing process than is assembling the end caps to the cylinder with rods and bolts like the repairable family of air cylinders.

As a result, non-repairable types of air cylinders are lower cost than a repairable cylinder of the same bore and stroke. Their method of assembly also means that this type of air cylinder is not typically disassembled for repair.

These air cylinders are also known as throw-aways, as that is what typically happens when they've reached the end of their useful life.

Perhaps the piston seals have worn so badly that the cylinder cannot generate any force, or the cushion seals are gone, or the impact of the piston on the end caps ultimately caused a component fracture. It could be that the relatively small diameter rods have experienced some sideloading which can damage the cylinder beyond repair.

Regardless, once they do not work properly, the appropriate destination is the metal recycling bin.

Recently some manufacturers are developed an all-composite throw-away air cylinder. Fairly low cost, low weight, high cycle, you might want to have a look at these for your application if you are seeking a non-repairable air cylinder for you equipment.

Non-repairable-air-cylinders offer a number of options that allow selection of the appropriate cylinder combination for the application. These options include a variety of mounting styles.

It is usually a good idea when purchasing a non-repairable cylinder (or any actuator for that matter) to select one that has been built to an industry standard so that, in the event your present brand of cylinder is not available in the future, you can substitute a cylinder with the same exact dimensions from another vendor.

Some additional options for non-returnable type air cylinders that might be required for a specific application are:

• Alignment couplers
• Block style mounts (either rod or back end cap is square with through holes for mounting)
• Clevis mounts
• Cylinder Cushions
• Double End rod (the rod protrudes from both ends of the cylinder
  
• Foot Mounts
• Non-rotating rod (perhaps hexagonal, or dual rod)
• Nose mount (usually standard)
• Proximity Switches
• Rear thread mount (often standard)
• Trunnion Style Mounts (trunnions can be rod end, rear cap or centrally mounted to allow the cylinder to pivot)

Non-repairable type air cylinders are available in bore diameters from under 1/2" to over 2 1/2". In metric sizes, bores are about 8mm up to 50mm as a norm.

What do you need to know to select the appropriate non-repairable air cylinder for your application? Here are some tips:

• What bore size? (How much force needed including allowance for friction inside the cylinder and a safety margin)
• What stroke? (What is the distance you want whatever's attached to the rod move? For longest cylinder life, the cylinder piston should never "bottom" at the rod or back end cap)
• Is the cylinder to be cushioned at one or both ends?
• Does the cylinder need a magnet on the piston for position sensing?
• How will the cylinder be mounted, and what are the dimensions of those mounts?
• How will the cylinder rod(s) be attached to the item you are moving?
• What are the port sizes, so you can be sure you have the correct air line fittings?
• Will flow controls be necessary for your application?
• Will the application require a lubricator, or will the factory lubrication suffice? High-speed cycle rates may require additional lubrication. Check with the cylinder vendor.

Non-repairable air cylinders have their place when a new piece of equipment is being designed. The speed with which replacement air cylinders can be acquired and their relatively low up-front cost, makes these cylinders a popular choice for equipment designers.