Insane Hydraulics
Bold and audacious blog about fluid power
Today's post is another reminder of how important it is to keep an open mind and not let mental inertia steer you on an obviously correct but not the easiest of paths if you want to be a "top tier hydraulic troubleshooter".
We, as hydraulic techs, work with systems filled with oil. It's a given. And it goes without saying that we expect our systems to be clean, not too hot or too cold, and air-free. And, of course, when we troubleshoot malfunctioning equipment, we test stuff, and testing, in a nutshell, is nothing but putting a "questionable" component in a controlled hydraulic environment and seeing how it responds to a known input. The key word here is "hydraulic environment".
"Well, what's novel about that? Of course, you test hydraulic components in a hydraulic environemnt, i.e. - with hydraulic fluid! Dah!" To which I respond: "You are right, but if "hydraulic fluid" is the only word that comes to your mind when you think about testing components, you're a victim of the most common cognitive bias found among hydraulic professionals - "hydraulic components work with oil, and therefore can only be tested with oil".
"Dude! We talk hydraulics here, right? Oil hydraulics! How else would you test them components, with compressed air?!!" - you burst into sarcastic laughter at this point. And I reply: "That is correct, my wonderful giggling friend, with air! I am talking about testing hydraulic components with compressed air, conveniently found in any shop in the world.
Madness!.. Heresy!..
Hold on for just a second and hear me out. I agree that hydraulic components should work air-free, and yet I defend the point that in certain situations a quick test with compressed air, which is something you can perform literally in seconds with the aid of a common shop blow gun and a bit of sound judgment, can pinpoint a malfunction that would take you incomparably longer to detect with "standard wet tests".
Compressed air can never replace hydraulic fluid, but it is exceptional in detecting unwanted leaks and blocked passages. You will never be able to use compressed air to quantify a leak, but when you are after binary checks - i.e. open or closed, leaking or not - you should always consider using compressed air. Simply because using compressed air is so much easier and faster!
A couple of weeks ago a friend of mine, who owns a repair business, was working on a skid steer. He overhauled the lift arm cylinders, the directional control valve, and replaced some hoses. He then called me asking if our test bench was available because he needed to test the DCV, and the matter was very urgent. I asked what the problem was and he said - "The machine's running just fine, but there's a leak somewhere and I can't figure it out. It's dripping oil from under a lever box, and I already replaced the spool seals twice! I could really use your help, man, I have to deliver it like yesterday! So I told him - "No chance today, but you can bring the valve over tomorrow if you want, but if I were you, I'd try finding the leak with compressed air first. Remove the lever box, the return hose, and blow into the T line with a blow gun - maybe you'll be able to see foaming somewhere. It's a quick test - if you find nothing, then bring the valve over and we'll deal with it first thing in the morning!"
Half an hour later the man calls back and says - "Dude, you were right! I found it! There's a bolt at the top of the spool and foam bubbles appeared from under it as soon as I hit it with the blow gun! Just a bad o-ring, the leak is all fixed now! Boy am I glad I don't have to spend half a day removing the DCV from under a rat's nest of hoses and another half a day putting it back in!"
Here's another example for you. From this week. Another client called and said that he was working on a telescopic handler's steering. For those of you who are not familiar with these machines - they employ all-wheel steering and usually have a directional valve that allows for three steering modes - single axis, double axis, and crab. The main complaint was that the steering worked, but one of the steering cylinders was falling out of sync pretty quickly, which suggested an internal leak.
His client wanted to have proof that the cylinder was problematic before giving an OK to such a labor-intensive and therefore expensive overhaul. The man wanted to test the steering cylinders, and his idea was to take each of them to the end of travel and then remove the low-pressure side connection to see if any oil was passing through, which would be a sure sign of a leaking piston seal, the only problem was the fact that there was a limit switch somewhere, that apparently was not allowing to pressurize the steering cylinder when a certain limit was reached (at least that's what I was told).
So he called me, saying that it was very complicated to remove the cylinders from the axes for "proper bench tests" and asked if there was anything else he could do to test the steering cylinder on the spot. So I said to him - yes, there's still a couple of things you could do, like finding a way to block the wheels mid-stroke, for one - but before you do anything "complicated", disconnect the cylinder lines and give one of the ports a "gentle blow" with a shop blow gun - if you see any air/oil coming from the opposite side and the cylinder's not moving - you just found your leak! No air should pass, period. Ten minutes later the cylinder was air-tested and the leak was confirmed!
You see, when we learn oil hydraulics, we are taught "from the crib" that air is our enemy number one, so we never consider it as our friend. But, believe me, it is! As soon as you learn that it is an alternative troubleshooting tool to quickly find leaks or blocked ways - you will see that sometimes, (not always, obviously) it is way easier and quicker to test stuff with air than with oil!
Make sure you always wear protective goggles when you do compressed air tests, though, because there's a good chance you'll spray yourself from head to toes with an air/oil mixture if you're not careful, and always start your air tests "gently" - with the lowest amount/pressure possible, and when you pressurize a large volume (like a cylinder chamber), make sure you drain the pressure slowly. You will get the hang of it eventually (after a few surprisingly amusing "oil showers")...
There are other ways to use compressed air if you are creative enough. In certain scenarios, it can even be a makeshift replacement of a low-pressure pilot source, for example. I am not saying that you should start testing everything hydraulic with a blow gun from now on. I just want you to override your "wet tests only" bias so that when you find yourself troubleshooting a hydraulic malfunction in the field, without the luxury of a shop with test benches and diagnostic tools at your disposal, you remember the compressed air technique.
Never forget - the best troubleshooting tool at your disposal will always be the one that's sitting between your ears!