Better Farming – September 2016

47 / 72

Better Farming September 2016 Farm News First > 47
Some of we older farm equipment
operators remember when we
had only hydraulically operated
three-point hitches, and possibly one
remote outlet for the trail plough,
cultivator or disc. The actual hydrau-
lic systems were relatively crude in
design, and great care did not have to
be taken to filter hydraulic fluids as
those old gear and piston pumps
could tolerate most anything that
came along, including some water.
Power steering soon followed and
the need for cleaner hydraulic fluid
became a little more critical as
manufacturers reduced component
tolerances.
About 1980 we began to see
piston-type hydraulic pumps and
motors that had tolerances of only a
few microns (µm). They were used
primarily for variable-speed drive
systems. They replaced the old
mechanical variable-speed drive
systems that we had used on combines
to give us infinitely variable ground
speed. That development allowed us
to better match ground speed to
cylinder loading and greatly improved
the combine field efficiency without
having to stop and change gears.
The newer piston pump/motor
systems soon provided us with very
sophisticated, totally hydraulic drive
systems for the large self-propelled
field sprayers that are now in com-
mon use. Farm input supply compa-
nies own many of these sprayers, but
large farm owner/operators now own
almost an equal number.
Those high pressure, low-clearance
piston systems did and do require
high quality, clean hydraulic fluid.
The piston clearance is often in the
three to five µm range! Can you see
HOW ITWORKS
by RALPH WINFIELD
Keep your hydraulics running smoothly with
regular maintenance
Today’s hydraulic system components operate with incredible precision and require
specialized understanding to maintain good working order.
particulate matter in that size range?
Not a chance! Even new hydraulic
fluid should be filtered into the
hydraulic tank.
Please remember that hydraulic
fluid is only screened into the pump.
It cannot be filtered into the pump.
The pump sends the fluid to activa-
tors and motors or cylinders. A filter
pressure drop at the pump input is
not acceptable as it can cause cavita-
tion. (A pressure drop could be
caused by a build-up of contamina-
tions in the filter.)
Cavitation is the change of the
liquid to a gaseous product in a
hydraulic system. Cavitation will ruin
a hydraulic pump! Gaseous fluid com-
pressed by a pump reverts to a liquid
with destructive forces. The resultant
scaly metal pieces will then contami-
nate the remainder of the hydraulic
system. A complete system cleanup
and rebuild is very, very expensive.
Understanding hydraulic systems
Every farm team which operates
newer hydraulic systems on tractors,
sprayers, combines, or other equip-
ment should have someone who is
knowledgeable about how these
systems work.
Based on my many years of
teaching, writing service manuals,
and observing people in action, I
think I have seen most of the mis-
takes people can and do make. Here is
one example:
A hydraulic function becomes
slow. Many people will look for an
adjusting screw in the hydraulic
system(s). Sometimes they will find
an adjustable pressure relief valve.
They will turn it in three or more
turns only to find that it does not
increase the function speed. Will they
turn it back out? Not likely. The
pressure relief setting therefore
increases significantly. So when the
speed fault is corrected, will the new
setting result in blown seals and/or
hose connections? You bet it will.
For this reason, most equipment
manufacturers use non-adjustable
pressure relief valves whenever
possible. Unfortunately, some pres-
This planting unit with no markers is planting soybeans (no-till)
into last year's corn stalks using a GPS as a marker system.