These are a few parts originated from a Sauer Danfoss series 90
closed loop pump that was brought over to our workshop for repair. The
main symptom was - "the machine doesn't work". The reason why the pump
had stopped pumping was discovered as soon as it was disassembled -
everything inside was covered with a very rigid and very smelly
varnish-like substance, which completely seized and glued all moving
parts inside the control module, as well as clogged all the sensitive
and not sensitive orifices. Clearly something very "chemical" had
happened with the hydraulic fluid. Hydraulic oil degradation and the
associated varnish and sludge deposits are no news to hydraulics
people, but this particular case was different, or better - more
uncommon, both due to the main reason that caused the appearance of the
deposit and to the chemical that was used to remove the smelly stuff.
Further investigation revealed that the misadventure
had happened during the regular maintenance stop of an all hydraulic
tomato harvester, in which both open and closed circuits were fed by
the same 200 liter oil tank. As a logical part of the preventive
maintenance plan the tank was topped up to the due level - after this
the machine started, worked for about ten minutes an then "died"...
It turned out that the twenty odd liters of "hydraulic
oil", that was used to top up the tank, was in fact some agricultural
bug-killing formula, that was very conveniently stored in an empty
hydraulic oil drum right next to other drums with hydraulic oil inside.
The mixture caused an incredibly smelly chemical reaction, that
resulted in the appearance of the very hard varnish-like deposit that
spread all over the hydraulic system!!!
Everything that was a spool got stuck and everything that was an
orifice got clogged. The culmination point was reached when the charge
pressure relief valve got stuck-shut, and the spin-on charge oil filter
was blown away from its place by the oil pressure!
It was clear that all the parts needed to be
thoroughly cleaned in order to make the pump function - so a series of
solvents were tried to remove the deposit. We tried petrol, gas,
kerosene, benzin, all sorts of thinners and spirits with no or very
little result - the deposit was incredibly resistant to all those
agents, and was very hard to be removed mechanically. You know
what solved the problem in the end (I mean - literally -
solved)?. Simple tap water!!! The tuff gluey deposit was completely
dissolved and removed by warm soapy water! Since the pump suffered no
mechanical damage, the repair process resumed to washing the parts and
assembling the pump (and the motor, of course...). As you can imagine,
the similar procedure had to be performed to the rest of the machine's
components, which was neither fast nor cheap...
This case brought me back to the time when we had
one of those parts washers that used hot water based solution - it
didn't stay for long, but I'm sure it would've been extremely handy for
this particular "cleaning".
