MACHINERY LUBRICATION- INDIA NOVEMBER-DECEMBER 2019 | Page 23

MLI
equal displacement, this will ensure they all
move at the same speed.
The problem with flow dividers is that even
new actuators will bypass different amounts
of flow. Regardless of how minuscule this
difference in bypassing may be, the actua-
tors can be significantly out of synch after
only a small number of machine cycles due
to the extreme tightness of the flow divider.
This is where adjustments come into play.
Crossport Relief Valves
Adjustments are made via crossport relief
valves. Many people assume the purpose
of these valves is to absorb shock. While
they will indeed absorb shock, their primary
purpose is to allow some slippage to keep
the actuators moving in synch. When the
actuator that is bypassing the least amount
reaches its stroke limit, the actuator that is
bypassing somewhat more will not be quite
at its limit. With the crossport relief valves
in place, pressure can build in the line of
the actuator that has reached the end of its
stroke until the crossport opens. Flow can
then continue to the slower actuator and
enable it to reach its limit.
A lot of flow dividers come with crossport
relief valves built in, but some do not. If
the actuators are mechanically connected, it
usually is advisable to either purchase a flow
divider with built-in crossport relief valves
or add a set of crossports to the assembly.
While speaking at a conference a few years
ago, I met a woman from the Department
of Transportation. After I had spoken, she
introduced herself and said she had attended
the conference in hopes of finding someone
who could offer some advice on a ferry ramp
that had recently been installed. Since my
topic included hydraulic troubleshooting,
she thought I might be able to assist.
The ferry ramp cylinder/flow divider
configuration
The ferry ramp was a relatively simple
hydraulic system but of a rather unique and
expensive design. Two enormous cylinders
were mounted on the ocean floor to lift and
lower the ramp. Since the cylinders had to
be installed by divers, each one cost more
than $1 million.
After installation, the ferry ramp worked
very well. The ramp would lift, the ferry
would move under it, and then the ramp
would lower onto the ferry so vehicles could
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