Very often I am asked about which is the best way to flush contaminated
lines of a closed loop that suffered a serious failure. This article is
a short description of one of the easy flushing techniques I've used
for years, and that hasn't let me down so far.
Closed loops are everywhere, and luckily for
hydraulics businesses they break all the time, causing workshop owners
to grin when a simple seal-kit pump overhaul is needed, to beam when a
rotary group needs to be replaced, and to laugh heartily while rubbing
(clapping) hands when a major failure causes a complete transmission to
drop by. All the grinning, beaming and laughing is performed after the client has left the room, naturally...
After a damaged closed loop pump or motor is
repaired and re-installed on the machine, a special care must be given
to circuit cleanliness and in particular to the loop lines, to
guarantee that the recently rebuilt unit doesn't "expire" the moment it
starts turning. This is especially vital in case of a major failure
caused interventions, because the loop lines get contaminated with all
sorts of debris, that can destroy the new transmission in a matter of
minutes unless removed from the circuit.
When the loop is simple and the hoses are short and
easy to dismount, a mechanical cleaning (brushes, air projectiles,
solvents, etc...) is an easy way to get rid of the contaminants, but
when the lines are extensive and the circuit is more complex, it may be
next to impossible to dismount and clean all the hoses, and in this
case a flushing of the loop is mandatory
before putting the machine back in service. There are various ways to
perform this procedure, and in some rare cases special equipment is
required, however most of the times the following simple technique
(aided, of course, by others re-commission must-dos and could-dos, like
mechanical cleaning, filter and oil change/analysis and common sense
application) is enough to ensure safe start-up of a closed loop.
The technique resumes to inserting pressure filters
in the loop and using the pump itself to provide the flushing flow
(along with actuator bypassing), which is exactly what you can see on
these pictures, that demonstrate the flushing procedure being performed
on a Parker RT 16 jaw crusher
- a beautiful and intimidating piece of machinery, equipped with two
closed loops that can work independently to pull on the caterpillars,
or in conjunction to spin the crusher motor.
The filter assembly, consisting of a pressure
filter, a check-valve and a relief valve is introduced into the loop as
close to the pump as possible, ideally - connected directly to the pump
with a previously cleaned hose. The purpose is to filter the oil that
enters the pump after flushing through the loop. The check valve
guarantees unidirectional flow - through filter to pump, and the relief
valve makes sure the filter/hose/check-valve isn't blown away in case
the pump pumps in the wrong direction, and is also a good "dude,
it's the other way round!!!" indicator. Here
you can see two filter assemblies (one for each pump, the relief valve
tank hoses aren't connected yet). You can also see the traction motors
and the crusher motor bypasses.
A quarter of an hour of full speed operation at
maximum displacement in both directions for traction and crusher
circuits was enough to catch most of the garbage (note that when the
flushing flow direction is changed, the filter position must also be
changed, although for many circuits simple one side flushing is enough,
not in this case though). The hoses were re-connected and the crusher
has worked ever since...
As you can see, this flushing technique doesn't
require much gear (compared to an external power flushing cart, for
example), and is relatively simple to apply. It does have
limitations, but is still a good and relatively cheap way to assure
healthy start-up for the majority of rebuilt closed loop
transmissions. I applied it countless times and always got positive
P.S. Once I got the crusher moving, I couldn't
resist the temptation of putting random everyday objects in the path of
the 50 ton critter.... Another child dream come true...