By Josh Cosford, Contributing Editor
If you work with a hydraulic technician who services and repairs hydraulics, especially including work on power units, leave this article for a moment and go ask them, “What’s the craziest thing you’ve seen inside an old reservoir?” My own answer isn’t so memorable; it’s just a half-collapsed suction filter that was entirely detached from the suction port. However, I once asked the same question of a colleague with three decades of experience, to which he grimly responded, “A raccoon.”
Indeed, such an experience warrants justification to the question posed in the article’s title. Apparently, hydraulic oil is a reasonable facsimile of formaldehyde, and a shocking amount of that poor animal was intact. But it certainly warrants complete drainage of the reservoir to clean any remaining organic matter, especially clumps of fur that can clog the suction strainer (if installed) and small ports, passages, and valves, as well as other components.
If you’re a regular reader, you know I don’t condone arbitrarily changing your hydraulic oil because all efforts should be made to clean and dry it, no matter what. But sometimes the entire system should be drained to allow for a deep cleaning, and part of the draining and refilling process requires a filter cart that cleans your oil twice during such maintenance. Unless your oil is near-black from oxidation or has the consistency of mocha hair gel, you can reuse it most of the time. But of course, those reasons for completely draining your oil are obvious.
In most cases, it’s obvious when you should drain your hydraulic oil, such as after catastrophic failures that result in rapid, excessive saturation with metal wear particles. A flashlight shone into the reservoir, will reflect back a metallic sheen, which is a sure sign that your oil needs immediate offline filtration. Thus, it should not be left to the machine’s filtration package to sort out. If larger chunks of metal or debris are discovered, you’ll need to drain the tank to pull apart valve stacks, cartridge valves and actuators you suspect were infected by the influx of debris.
Pulling off a D05 valve from an assembled hydraulic system causes a small stream of flow as higher components drain, at best. Still, suppose huge cylinders, lines, accumulators or the reservoir itself reside higher than your valve, you can expect your manifold to drain with the vigor of a New York City fire hydrant opened for children on a sweltering summer day. So, unless you have a method to block your oil from taking the path of least resistance, replacing major components often warrants draining the hydraulic oil.
Sometimes there are accidental reasons to drain your hydraulic oil, such as a massive influx of water from rain, submersion or a fire suppression system that found its way into the breather cap. Luckily, water settles to the bottom of the tank, so be sure first to use the tank’s drain port rather than suck it all out with your filter cart, which will just deposit itself into your temporary holding container, where it will wait to be transferred right back again if not dealt with.
Finally, sometimes the footsteps of time sneak up on you from behind, and a few decades of operational sediment needs to be scraped and scoured from the bottom of the reservoir. Experienced technicians know to stick a long, thin object down to the bottom of a reservoir suspected of neglect and drag it across the bottom to feel for bare steel or a sandbar. If the latter is discovered, it’s time to drain the reservoir and clean it thoroughly.
Completely draining your hydraulic system is a lot of work, and I really do recommend you do so only with a filter cart, since the primary reason we drain them is to remove contamination. There’s no point in refilling it with dirty oil, because the whole point of draining your hydraulic system is to clean it.
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