One of the "baddest" machines a hydraulic technician may have to battle is the hydraulic excavator. These multi-function mechanized monsters come in all sizes, forms, and brands, and get more complicated with every passing year, having become a real "troubleshooting nightmare" for anyone but those who have privileged access to detailed technical documentation, in most cases kept behind armored OEM's doors.
This is the main reason why I stick to pumps, motors, and standard component hydraulics. Every "protected" pump can be reverse-engineered in a workshop environment because you can strip it down to the smallest screw - something you can't do to a twenty-ton machine. When you deal with a modern hydraulic excavator, you deal with a very complex piece of hydraulic equipment, which still can be back-engineered, but the final cost and the time spent during the process don't justify it most of the time.
"Most of the time", however, doesn't mean "all the time", and since a good half of the pumps and motors that pass through our workshop come from rotary excavators and excavator-based equipment, I occasionally happen to come in close contact with these noisy toys.
When the hydraulic schematic is available, troubleshooting becomes a relatively straightforward process of logical elimination of probable causes. In such cases, my main objective is to determine where the problem is and if I can repair it. When the hydraulic diagram is not available, the troubleshooting process becomes a two-stage endeavor. The first stage is "getting to know the equipment" and the second stage is the "troubleshooting itself". The first stage is the most important one since you can not troubleshoot something you don't know! You must have a good understanding of how a hydraulic circuit works before elaborating any troubleshooting theory, otherwise you end up doing this!
This first stage is, therefore, all about back-engineering, and in the case of mobile machinery it usually resumes to:
a) hose pulling (to see what's connected to what) - an incredibly arduous, irritating, and tedious exercise due to the compact nature and most of the times remarkably crappy condition of the hoses, and
b) component disassembly (to see what's inside and how it works) - another task that can become incredibly challenging due to the field conditions earth-moving equipment usually operates in.
Despite giving tons of trouble, this process can also bring you tons of true satisfaction when you finally confirm your theory and prove once again that knowledge of basic hydraulic component back-engineering strategies is an extremely valuable skill!
One of the times I "shined" (referring to my back-engineering know-how here) was a couple of years ago when a friend of ours from the Santa Maria (Azores islands, a Portuguese archipelago in the middle of North Atlantic) asked if I could take a look at one "strange brand" excavator that had been immobilized for more than a year.
The Azores is one of the most beautiful places on the Earth, and I had the privilege of visiting this destination many times (thank you very much, hydraulics), so I was well aware of the fact that, while on the main island (Sao Miguel) hydraulic supplies were relatively easy to obtain, more distant small islands (like the Santa Maria) were industrial deserts lacking everything, even the simplest stuff like fittings and gauges, so I grabbed all the gear my weight limit allowed (plus a couple of extra pounds in the back-pack) and caught the first flight to the Santa Maria.
Flying with hydraulic stuff... What an experience! Opening your luggage and describing to armed officers that what you are carrying is not a bomb, but a digital pressure gauge, a flow-meter, a valve, etc... With the biggest confusion in this country being caused by the fact that in the Portuguese language the word "pump" and the word "bomb" are the same word - "bomba" - so even when I bring along pump parts, I should be very careful to never ever say that they are pump parts (bomb parts)!
Anyhow, the machine in question was this small wheeled Furukawa digger.
Apparently, it was not moving due to the insufficient pilot pressure. No need to say that no hydraulic schematic was available. A sheer amount of hose pulling and a couple of pressure readings narrowed the malfunction down to a manifold that held various unknown valves and had multiple hose connections running to it:
Since I had no information on what was inside the manifold, but was sure that it was supposed to supply the joystick pilot pressure, I decided to dismount it from the machine and do the one thing I liked doing the most with unknown hydraulics - reverse-engineering.
For a couple of hours, curious standers-by watched me blow through the manifold openings with an air gun (sprinkling all around me with oil), shove wires in holes, inspect them with a flashlight, disassemble all of the valves down to the smallest pieces and make strange doodles on a piece of paper. I bet the thought "poor chap's gone koo-koo" passed through more than one head that day...
But in the end, I knew exactly what the manifold valves did, and with certainty narrowed the malfunction down to one single pressure reducing valve. On a closer inspection it turned out that the valve stopped functioning properly due to the appearance of a wear groove on the small ball in the pilot section - the groove was so deep that the ball couldn't seat properly, resulting in an oil leak and the consequent low pilot pressure. The ball was replaced, the manifold re-assembled and re-mounted, and - Alleluia! - the machine moved, for the first time in more than a year!
It felt extremely satisfying to witness yet another evidence that all that time I spent back-engineering hydraulic stuff and studying designs paid off!
Note, please, that this post is me praising reverse-engineering and not me bragging about my troubleshooting talents!
People often ask my opinion on hydraulic equipment they want to buy. I always answer - buy the one that comes with a hydraulic diagram!