Service Manual

Building A Basic Circuit (Cont’d)
This cycle is repeated until the cylinder ram is
fully extended. Notice in the simplified system,
the ram can not be let down.
To accomplish this,
we need to add a second valve under the
cylinder. This valve should not open unless the
pressure capacity
of the system is met or it is
manually opened to let the cylinder ram down.
A
return line will direct the oil from the cylinder
back to the reservoir.
Building A Lift System
Let’s replace the hand pump with an external
gear pump which is capable of providing
constant displacement and more flow.
By placing the pump in-line, we no longer need
the check valves to provide directional control.
The greater output of this pump will extend the
cylinder much faster. When the cylinder ram
reaches the end
of its stroke, pressure will
increase and open the relief valve.
If we replace the single action cylinder with an
open center spool valve and a dual action
cylinder, we have a basic lift system.
When the spool valve is centered, the oil passes
directly through it and returns to the reservoir.
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Productivity Series