Better Farming February 2017

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78 Dig Deeper: Better Farming February 2017
HOWIT WORKS
performance. Figure two illustrates
the dirt-loading characteristic that
follows, as well as the resulting
pressure drop that occurs across the
filter.
Dirt loading of filter elements
Performance rating is very important
but it also raises the question of how
much dirt a filter can hold before the
pressure drop across the filter be-
comes excessive.
The rapid rise in pressure drop
across the filter occurs after a relative-
ly long time, even though the dirt
addition was continuous. What this
means is that every hydraulic fluid
filter should have a pressure-
monitoring device in place so the
operator can observe pressure drop
– but especially any sudden pressure
rise. A sudden rise often effectively
indicates a component failure in the
hydraulic system.
On “cold start up” of a closed-
centre hydraulic system, the fluid can
and will temporarily bypass the filter.
Virtually every filter head has a
25-pound per square inch (psi) relief
valve to permit fluid bypass. A
pressure gauge can be placed at the
filter location or preferably moved up
to the operator dash. A light, usually
red, can also be used to alert the
operator when a filter bypass is
occurring.
If the light stays on after the fluid is
warmed, the filter should be changed
immediately. The question of chang-
ing the fluid is up for debate. If you
have access to fluid testing by an
equipment dealer or an outside party,
it is probably well worth the cost.
A fluid test indicating a high level
of contamination might indicate that
there is or has been a mechanical
component failure. See the photo on
page 79 of a failed bearing compo-
nent. When a mechanical component
failure has occurred, a total hydraulic
system cleanup is essential.
Unfiltered lubrication
Many small gear sets, such as sun
and planet gear sets (often located
directly at drive wheels), do not have
filtered lubricant available. It is
critical that the small quantity of
lubricant be changed regularly.
Gear sets located at the center of
virtually every mechanical front
wheel drive (MFWD) tractor are
prime examples of these small gear
sets needing regular lubricant
changes. If a MFWD tractor is used
regularly – especially in the winter
– that gear case should be drained
and flushed at least once a year. You
will probably see some small metal
flakes in the fluid which will give it a
yellow or golden colour.
Planetary gear sets cost much
more than the cost of materials and
the labour required to flush those
units once a year.
Many other final drive gear cases
on combines, etc. should have the
gear oil changed on a regular sched-
ule – probably once a year. Check
with the operator/service manual or
your dealer.
A pressure gauge will indicate fluid bypass and/or filter condition.
A prewired red light from a pressure transducer is even better.