Proper, consistent cylinder maintenance is necessary to keep your fluid power systems running smoothly and efficiently. Following these five tips is a step in the right direction.
1. Keep your oil clean. This should go without saying, but I wouldn’t have to say it if the majority of hydraulic failures weren’t still from contaminated oil. Filter your danged oil. Dirt particles love to move back and forth inside a cylinder, so it’s especially important to ensure oil is clean the first time it makes its way into your cylinder.
Install high-efficiency filters in your hydraulic system, and ensure they’re changed when required. A differential pressure gauge or pop-up indicator can tell you when a filter is clogged, which will allow you to change it out before it goes into bypass, a condition when oil passes through the housing unfiltered.
2. Inspect your cylinder regularly. Have a look at the condition of the rod for corrosion, pitting and uneven wear. Corrosion could signal excessive moisture, either ambient or within the fluid. The latter scenario is worse, as it spells disaster for your entire hydraulic system. Rod corrosion will accelerate seal wear, as friction damages the rod seal and wiper. Pitting on the rod can occur from corrosion, but also from physical damage, which will also lead to seal damage.
Uneven wear of the rod is often a result of misalignment. Side load causes the rod to rub on one side of the bearing, which can prematurely wear the bearing, seal(s) and rod itself. In most cases, a corroded and damaged rod can be re-chromed and/or polished to refinish it. If the rod can’t be repaired, it can be manufactured by any cylinder repair shop. Before re-installation, it would be wise to remedy the problem causing the damage in the first place, or you will find yourself in the business of changing the cylinder often.
3. Rotate your cylinders. If downtime is an absolute impossibility, you may want to keep a set of spare cylinders you rotate into service on a regular basis. This will keep your cylinders fresh in spite of high risk particle contamination or extreme operating conditions. Once one cylinder is removed from service, it can be disassembled, inspected and repaired if required.
When a cylinder is in pieces, it’s a good idea to replace all seals, since they’re typically very economical. Inspecting the internals of your cylinders on a regular basis also gives you clues to the condition of the rest of your hydraulic system. The occurrence of varnish, for example, could mean your oil is running continuously hot, and you may need to address operating temperature.
Also, a physical inspection of the piston and cap can tell you if particles have been trapped within the cylinder. If it looks like someone was beating your piston with a ball peen hammer, then I can guarantee a chunk of metal has been slapping around inside for months or years. And if it made its way into your cylinder, it existed elsewhere in the system, too.
4. Service your accessories. The brackets, clevises, rod eyes, ball joints or other connections to a hydraulic cylinder are nearly as important as the cylinder itself. When a pivot pin or clevis is worn, there is excessive slop and play in the joints of the cylinder. This will cause misalignment, which could lead to rapid wear or catastrophic damage in some cases.
If you have a high precision machine, even a few thousandths extra clearance between each joint can cause jerky, inaccurate motion and vibration. When a cylinder is removed for servicing, it is a best practice to inspect and replace the accessories, if needed. A pin is only a few bucks, and is meaningless compared to a thousand dollar NFPA cylinder. Just as with other parts of your hydraulic machine requiring lube, grease the cylinder joints on a regular basis to prevent uneven or excessive wear. An ounce of prevention goes a long way.
5. Inspect your lube oil system. If you are running pneumatic cylinders, which often need their own source of lubrication, inspect and service your lubrication system, as needed. A basic system will have a lubricator built into the filter/regulator assembly, which is fairly reliable. However, no lube oil can be provided when the reservoir is empty. Inspect the oil level regularly, and top off as needed.
Even a reservoir full of oil provides no guarantee your lubricator is working, so you may need to test your oil line exiting the FRL by hooking up a blow gun and spraying a white paper towel. If there is a patch of oil on the towel, you’re good to go. If it is dry, you may have to remedy a clog in the lubricator, or replace it if it cannot be fixed.
When testing any lubrication system, check that excessive amounts of oil aren’t being introduced into the system. I’ve seen lube systems introducing so much oil as to hydrolock a pneumatic cylinder, preventing it from cycling full stroke rapidly. Only a fine mist is required to help an air cylinder overcome friction.