One of the baddest machines a hydraulic technician may have to "battle"
with is a hydraulic excavator. These multi-function mechanized monsters
come in all sizes, forms and brands, and get more an more complicated
every 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 afford doing with 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 doesn't justify it most of the times.
"Most of the times", however, doesn't mean "all the
times", 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 a hydraulic schematics is available
(happens ve-e-ery rarely), troubleshooting becomes a relatively
transparent process of logical elimination of probable malfunction
causes. In such cases my main objective is to determine where the
problem is and if I can repair it (I don't repair electronics and
software related problems, for example). When a hydraulic diagram is
not available, the troubleshooting process becomes a two-stage task.
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 may end up doing something like this!
This first stage is, therefore, ALL about back-engineering, and in case of mobile machinery it resumes to:
a) hose pulling (to see what's connected to what) -
an incredibly arduous, irritating and bewildering exercise due to the
compact nature and most of the times remarkably shitty condition of
them hoses, and
b) component disassembly (to see what's inside and
how it works) - another challenge due to the same above described
reasons.
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!
The last time I "shined" (referring to my back-engineering
know-how here) was a couple of weeks ago, when a friend of ours
from the Santa Maria (Azores islands, Portuguese archipelago in the
middle of North Atlantic) asked if I could take a look at one "strange
brand" excavator which had been immobilized for more than a year.
Azores archipelago is one of the most gorgeous
places on the Earth, and I had the privilege of visiting this beautiful
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-desert-like places, 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 Sta Maria.
Flying with hydraulic equipment test gear is one
matter that deserves to be described separately. I confess that I've
become used to opening my luggage and describing to armed officers that
what I'm carrying isn't a bomb, but a digital pressure gauge, valve,
flow-meter, part, etc... With the biggest confusion being caused by the
fact that in Portuguese language the word "pump" and the word "bomb"
are the same word (honest!), so even when I bring along pump parts, I
never ever say that these are pump parts (bomb parts!) and humbly call
them "motor parts", making everybody happy...
Anyhow, the machine in question was a small wheeled Furukawa
(a rare name in Portugal), which apparently was not moving due to the
insufficient joystick pilot pressure. No need to say that no hydraulic
schematics was available. Sheer amount of hose pulling and a couple of
pressure readings narrowed the malfunction down to this manifold,
which held various unknown valves, and had multiple connections. 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 mist, myself included), shove wires in holes,
inspect them with a flashlight, disassemble all of the valves to small
pieces and make some strange doodles on a piece of paper. I bet the
thought "the guy'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 appearance of wear groove on the small ball in the
pilot section - the groove was so deep that the ball couldn't seat
properly, resulting in 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 was an enormous satisfaction to witness yet
another evidence that all that time I spent back-engineering hydraulic
stuff and studying designs paid off!
Note, please, that this article should be considered
as me praising reverse-engineering and not me bragging about my
troubleshooting talents.
P.S. People often ask my opinion on which
hydraulic equipment to buy. I always answer - buy the one that comes
with a hydraulic diagram!
