Insane Hydraulics

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Oil Hydraulics and the Sixth Sense

In this article, I will talk about the "sixth sense", and how you can and should use it when you work with hydraulic systems.

As usual - I will start with a story:

Last week was all about coincidences! First - a friend of mine called and asked me to have a look at the hydraulic pump from his truck. When he arrived, he showed me a bent axis fixed displacement unit that was busted beyond repair.

How many hours does it have? - I asked - It looks so new! - Well - he said - it is new! How come? - Yeah... about that... so I was overhauling the tipper hydraulics and decided to re-arrange a couple of hoses... and I kind of sort of may have accidentally left a rag in the valve inlet...

Yep - there you have it, folks! A thousand bucks down the drain! Unfortunately, that was not the first time I saw something like that. (In fact, I even have a post on a very amusing rag-related experience of my own) - but that is not what I want to talk about. Yes, with hydraulics - when you forget things - you break things, often expensive things - but that's a given. What I found very interesting and worthy of attention was the feeling that the guy described to me. Let me explain:

The guy told me that he did everything he'd done countless times before. And as he was testing the system - he knew immediately that something was not right as soon as he began lifting the clutch pedal. He told me that he heard a difference in the noise the truck engine was making, he felt the increasing vibration of the loaded engine - he even pressed back on the pedal as soon as it happened and said to himself - Hmm, this is strange!... And yet, despite the subconsciousness screaming at him that something was very off, his conscious mind told him - "don't mind the other guy, man, we got more stuff to do!" So, he let go of the clutch and heard a big "bang" coming from under the chassis!

Anyhow - the guy bit the bullet and bought another pump. And now a story of my own, from this same week, also involving a tipper truck.

A new client called and asked me to check the hydraulics of his tipper truck that was "not lifting". It was a small 3,5 ton Mitsubishi Canter he bought second hand - and he told me it had "automatic lowering". Interesting.

When the truck arrived, it took me five minutes to find the cause of the "not lifting". The system consisted of a PTO, a gear pump, a solenoid-operated two-way valve for lowering, and a single-acting cylinder equipped with an end-of-stroke. The end-of-stroke valve was stuck, by-passing oil to tank, and a couple of "gentle taps" solved the problem. I was still intrigued by the "automatic lowering" function though, but as soon as the tipper began to lift again, I saw what was going on.

The truck operated in the following manner - the operator would press on the clutch pedal, engage the PTO, and then release the clutch to lift the tipper. And then, when needed, he would disengage the PTO - and the tipper would immediately (automatically!) lower with a buzzing sound z-z-z-z-z-z.

When I asked the man how he stopped the tipper mid-stroke and where was the button for lowering, he told me that it was not possible, he'd never used any button for the tipper control, and he was genuinely surprised that it was even needed.

So, I checked under the chassis again, and sure thing - there was no check valve in the pump line. So when the man would disconnect the pump from the PTO, the oil would flow back to the tank through the pump, and the buzzing sound was the pump rotating the other way around.

I installed a check valve in the P line and then discoverer an unmarked button on the dashboard that was controlling the solenoid valve. Boy was the man surprised to find out that his tipper could be stopped at will in any position and lowered with a push of a button!

Now - where does the sixth sense fit in all of this? Wait till you hear the rest of the "check-valve" story:

The pump outlet was connected with a single hose with two female ends - classic. So I (very pleased with my lighting-fast troubleshooting) grabbed a half an inch check valve and a couple of fittings - one male and one female - so that I could disconnect the hose end from the pump and install the check valve directly at the pump outlet.

So far so good. And, since I knew that a check valve in a hydraulic system should be treated like a hand grenade, especially when you install it in the outlet of a fixed displacement pump - I made sure to double, no, triple-check its direction.

Then I got on a creeper, slid under the truck, and began the installation. I disconnected the hose from the pump, installed the valve, connected the hose end to the valve and then I realized that it was a little bit unprotected, and was placed at the lowest point of the truck, pretty close to the ground - any impact would probably break it off - so I traced where the hose went and found that the other end of the hose was in a much better and a much more protected spot. Great! I reconnected the hose back to the pump, disconnected the other end of it, and installed the check valve (as it was) on that side.

As I was tightening the connection I felt that "something didn't feel right", so I decided to investigate. I thought to myself - "Maybe I should verify the check valve direction one more time, just to be on the safe-safe side..." So I grabbed a flashlight, and of course, the markings were not visible, so I had to loosen the connections to turn the valve around, and... am I seeing this right? The valve was mounted in the wrong position effectively blocking the outlet of the gear pump!

That was the moment when I face-palmed myself, which was not easy given I was lying on a creeper under a pretty low frame. Of course - when I threaded the male/female fittings into the check valve, I was "aiming" at the hose end that was connected to the pump, and when I moved the valve to the other end of it, I should have swapped the fittings as well - which I did not!

I am so glad I listened to the voice in my head...

So - why am I telling you all this? Here's why:

I believe that the subconscious part of our brain registers things much faster than the conscious, which is always busy doing many things at the same time (like answering a phone while working a spanner) which is why I have developed a habit of always investigating when something doesn't feel right. Whenever my gut tells me that something is "off" - I always listen to it, and always stop whatever it is that I am doing and look for things that can go wrong. This habit has never failed me!

Can you imagine what would have happened if I started the truck? It would be like - "just wait for another 10 minutes, sir, I'll install the check valve, and you will be good to go!" And then, ten minutes later - "Great news! You have been randomly selected to get a free PTO and a gear pump upgrade by our "You broke it - you fix it" department"...

I am telling you - this habit has saved my neck more times than I can remember. It takes time and practice to develop, but if you learn to "listen to your gut" - you'll be a better tech. The script is always the same - feeling that something is not right? Stop, take a step back, and think about what can go wrong in the current situation - most likely than not something is about to.

I am not ashamed to tell that I made the classic mistake of mounting a check valve the other way around - I am glad I did because it once again proved how important the "sixth sense" is. And I am glad that I can share it with you so that you never make such a mistake yourself.