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Mike Bacon, Internal Technical Applications Engineer at Matara, addresses the issue of quality when it comes to pneumatic cylinders: what constitutes quality, why does quality matter and, just as importantly, when does it matter.
From its origins in the first part of the 19th Century, pneumatic cylinders have been used in countless industrial processes around the world to move something along a linear path. A relatively straightforward mechanical device, pneumatic cylinders use compressed air to drive a piston inside a cylinder. The piston rod transfers the force it develops to the object to be moved.
Although it depends on the application at hand, pneumatic cylinders are often preferred to hydraulic cylinders as they don’t come with the associated risks of leakage and cross-contamination. Furthermore, they are quieter and, overall, take up less space as there is no requirement to store fluid.
Over the years, a wide array of pneumatic cylinders has been developed to meet specific needs, including roundline, guided, precision slide, compact, clamp and stopper cylinders. Rodless pneumatic cylinders are also available - and becoming more popular - which have been design to perform as a self-contained linear actuator for improved flexibility.
As with all mechanical devices, quality differs between types of pneumatic cylinders and between manufacturers.
When it pays to invest in quality
Whilst I’d like to say that quality always matters, the reality is that quality matters more in certain applications.
When it comes to miniature ‘brown’ cylinders, typically used in moving items off a conveyor belt for example, these are generally low cost items that don’t tend to be long lasting. You could invest in better quality versions but the return on investment doesn’t add up, mostly because they are very low cost so it’s not worth repairing them, and they are incredibly easy to replace – you literally swap out the broken one with the new one in ten minutes.
Where quality most certainly does matter is when it comes to the bigger cylinders - 125, 100, 6200 bore cylinders – which are lifting heavy weights. Replacing a big pneumatic cylinder is costly and rarely quick, as they generally aren’t stock items and therefore have to be machined and cut, which could easily take several days. At Matara, we have a large UK based machine shop and are able to build many pneumatic cylinders in-house, which means we can frequently deliver a replacement cylinder in two to three days, but that isn’t the case for all suppliers. Time is also required for the on-site engineers to fit the replacement, which will take several hours, not minutes. All of this time is clearly disrupting the process at hand. That’s why you really want these larger cylinders to be reliable, repairable (where possible) and long lasting.
Then, of course, you have the health and safety implications to take into account, especially if the cylinders are lifting several tonnes of machinery or items vertically. The last thing anyone wants in this scenario is the cylinder to fail and everything to plummet. If this did happen, other machinery could be damaged and you would probably have to shut down the whole area, which could last for days. To skimp on the cylinder, saving a few pounds, really wouldn’t be a good idea here.
What constitutes quality in a pneumatic cylinder?
As I’ve said, pneumatic cylinders are fairly simple devices in that they’re composed of just three or four parts. This actually makes it quite straightforward to tell when they're not good quality by just looking at them. Typically, there will be gaps, such as around the seals, and they may not quite line up.
But there are other important aspects to consider when assessing the quality of a pneumatic cylinder that need you to probe a little further.
Let’s start with the materials used in the construction of the cylinder. Aluminium, steel and stainless steel are essential. When it comes to the rods, chromed rods are ideal if the cylinder will be lifting heavy weights as these are far less prone to breaking. The seals are the items that are most likely go wrong on a cylinder as they can be easily damaged, especially in dirty, dusty site. In harsher environments, it pays to invest in better quality seals. In food environments, for example, corrosive resistant stainless steel seals would be a good option, but there are also PTF, PTFE and wiper seals.
To ensure you end up with a pneumatic cylinder that meets the demands of your site and application, its important that the manufacturer is able to offer a range of accessories. These include external accessories, such as mountings and crevices, and accessories fitted within the cylinder itself, including scrapers and bellows to protect the rod from dust and debris. Not every manufacturer will have a comprehensive range of accessories, but the better known, better quality ones will. At Matara, we produce a range of accessories including clevises such as male/female, rear and offset variations, as well as flange mounts, flow controllers, foot brackets, and reed switchers.
Next, check that the pneumatic cylinder adheres to the relevant standards: ISO 15552, ISO 21287 and ISO 6432. All reputable companies manufacture to those international standards, so that shouldn’t be an issue. What is an issue though is how those manufacturers test their products. Avoid batch tested products as you cannot be sure your specific cylinder has been tested. At Matara we test each and every cylinder we manufacture in house, which means we very rarely have any returned.
Lastly, what level of support can the manufacturer bring? This is a much under valued area, but one that definitely impacts the overall quality of the product and service. Is the manufacturer willing to visit site and provide advice on the cylinder? Maybe it can be repaired rather than replaced. Would a high temperature seal solve any issues?
Don’t forget maintenance
No matter how good quality the pneumatic cylinder, regular maintenance will help reduce unexpected downtime. This will generally involve checking the cylinder, tube, and rod seal for damage and applying lubricant where necessary. As the seals are most prone to damage, pay particular attention to these and replace where necessary. Matara supplies seal kits which make this process very straightforward.
Keeping the pneumatic cylinder clean also pays dividends. In particularly dusty environments it’s worth considering an easy clean cylinder where the surfaces are smoother all around so they don't collect dust and debris in the first place and can be easily cleaned. Tie rod cylinders are also slightly easier to clean as well.
Horses for courses
Ultimately, the nature of the site and the cost implications of repairing or replacing a pneumatic cylinder are the determining factors in just how much you are willing to invest in them. If it’s a hostile environment or one where hygiene is paramount, such as food or pharmaceutical, then quality really does matter. Choose well and your pneumatic cylinder should perform reliably and consistently for a long time. We were asked to replace a Matara cylinder recently that had been operational for over 13 years, which is an astonishing length of time to be fully operational. It goes to show that quality counts!
Based in the UK, Matara is a linear motion, automation and pneumatic component specialist. For more information go to www.matara.com