As the range of pneumatic cylinders available on the market today becomes more extensive and sophisticated, it can be challenging to ensure you’re maximizing the ROI available from your application.
There are many recommendations and tips that plants and machine builders can follow to help shorten the payback period for investments in pneumatic cylinders. Here’s some best practice advice on how engineers and specifiers can convert necessary outlays into returned investments.
1. Avoid side-load mounting
Cylinders are designed to deliver push-pull stroke action, so side-load mounting can result in a number of performance problems, including misalignment, off-centre loads, rod deflections, imprecise tie-rod torque or long stroke action.
Upon installation, the cylinder piston rod should be aligned with the mating machine component and then inspected in both the extended and retracted positions. Improper alignment can lead to excessive rod gland and cylinder bore wear, resulting in a shortened lifespan for the cylinder and lower productivity. Both of these unwanted effects only serve to extend the payback period.
2. Prevent Contamination
Also, consider how contamination can be prevented as this will further maximise the life of the cylinder. Particulates, pipe rust, scale and thread sealant debris can all curtail the life of the seal and plug openings, and damage surface finishes. So until the system is fitted with piping, keep the port plugs supplied with the cylinder in place and be sure to clean the piping thoroughly before making connections.
Moisture is another key factor to consider when trying to stop contamination, as when moisture collects in components in all compressed air systems it blocks the outlet flow-through. This can be potentially damaging to the performance of the cylinder as it can lead to diluted pre-lubrication grease, contaminated airline lubricants, a damaged barrel or rod finish, and the potential to freeze in cold weather.
To avoid this happening, consider using stainless steel cylinders such as Parker's P1S, which features a smooth, hygienic exterior design to prevent contamination. These are particularly useful for food industry applications as cleanliness is assured via the use of stainless steel piston rods, cylinder tube and end covers.
Plus, the end covers have no recesses or other grooves that can collect unwanted contaminants or bacteria, while the scraper rings, piston rod bearings and seals are made from self-lubricating materials to allow for regular washing and degreasing of the piston rod.
A final consideration when thinking about preventing contamination is to watch out for oils that result from air compressor lubrication carryover or synthetic oils which are typically incompatible with air-line components. Such oils can swell the seal and plug openings. Instead, consider using oil-compatible seals.
3. Use the appropriate seals and cushioning
Poor selection of seals can cause degradation, leading to the ingress of particles and dirt, which ultimately risks cylinder failure; therefore it is imperative that ‘fit for purpose’ choices are made to ensure the maximum lifetime and to guarantee productivity.
The end application drives the selection of wiper seals. For example, applications that are extremely dusty or feature very high operating temperatures will require appropriate seals to match the installed environment.
In terms of cushioning, this is directly linked to the lifetime of cylinders. Cushioning is required to decelerate a cylinder's piston before it strikes the end plate. Reducing the piston velocity lowers the stress on cylinder components, increasing the usable lifespan and ROI.
Whilst cylinders that feature automatic adjustment exist, a best practice recommendation is to use manual variants to achieve optimal cushioning, as you are able to match the weight of the workpiece to the dynamics of the movement. This method has been found to be much more accurate and efficient.
It’s well documented that cylinders operating at high or fast cycle rates will typically generate significant shock loads at end of stroke. Furthermore, the heat generated by the system can exceed the component’s temperature limits and affect the lubrication. With this in mind, consider selecting a pre-lubricated or air-cushioned cylinder.
Other options include adding a shock absorber or lowering system pressure via a regulator on the return (non-working) side of the cycle. Finally, adding flow control to the cylinder can also help, as long as high speed is not required.
As many engineers will be aware, running cylinders over their capacity applies high levels of stress and unwanted friction to seals, resulting in broken rod ends and disintegrated actuators. In addition, if the system contains speed control or energy-absorbing devices, then pressure spikes can double or triple normal system pressures. As a result, engineers should make sure rod accessories are shouldered firmly by threading all the way down or by using spacers or shims. Alternatively, consider increasing the rod thread size or using a studded rod end.
There are plenty of best practice procedures that can help plant engineers and machine builders maximise return on their investment in pneumatic cylinders. What’s more, most only require minimal time and effort to investigate, with any subsequent investments within reach of most budgets.
Find out how to make further changes to optimise the pneumatic valves on your plant with our post on Know Your Pneumatics: 3 Ways to Adopt Advances in Pneumatic Valve Technology
Article contributed by Franck Roussillon, product manager for actuators Europe, Parker Hannifin, Pneumatic Division Europe