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Figure 1-5. Mini-Valve in Neutral Position
c. Mini-Valves
The operation of the mini-valves is identical for all
table functions except the elevation and brake
circuits. These two hydraulic circuits use a 3-way
(single check valve) type mini-valve. All other func-
tions use a 4-way (dual check valve) type mini-
valve.
Either type mini-valve is controlled by two pushing
type, electrically operated solenoids. The sole-
noids push the spool valve (located in the lower
portion of the valve) one way or the other. This
motion opens the main supply galley (which has
pump pressure) allowing the oil to flow through the
various parts of the mini-valve to the function. The
spool valve also opens an oil return circuit which
allows the oil to return to the oil reservoir.
The main components of the mini-valve and their
functions are listed below:
1. Spool Valve - Opens the main oil galley
(pump pressure) to either mini-valve outlet de-
pending on which direction the spool valve is
pushed. Also it provides a return path for the oil
returning back into the reservoir.
2. Pilot Plunger - There are two plungers in a
four-way mini-valve (one in a 3-way mini-valve),
one under each check valve. The purpose of the
pilot plungers is to mechanically open the return
check valve allowing the oil to return back into the
reservoir.
3. Check Valve - Two are provided in each four-
way mini-valve to seal the oil in the cylinders and oil
lines and prevent any movement of the table. One
check valve is provided in a 3-way mini-valve.
4. Speed Controls - There are two speed
controls in each 4-way mini-valve. They are needle
valve type controls which restrict the volume of oil
returning back into the reservoir, thereby control-
ling the speed of the table surface movement. A 3-
way mini-valve has only one speed adjustment.
The speed controls are always located in the return
oil circuit to allow the movement of the cylinder to be
controlled. Also, by using this control method, it
does not matter what size cylinder and piston is
used because the speed is controlled by restricting
the return oil. If the pump puts out more volume to
a slave cylinder than is allowed by the speed
control, the pressure relief valve opens and pro-
vides an alternate path for the pump oil to return to
the reservoir.
The following material depicts the three operating
positions of the mini-valve. The movement of the
slave cylinder piston (extend or retract) is deter-
mined by which port of the Mini-Valve is activated.
Mini-Valve in Neutral Position
(No fluid flow) See figure 1-5.
• Spool Valve Centered - This closes off both oil
pressure and oil return galleys.
• Pilot Plungers Both Closed -The pilot plung-
ers control the opening of the check valves. If they
are closed, the check valves must be closed.
• Check Valves - Both check valves are closed
trapping the oil in the cylinder and oil lines.
• Speed Control - When the mini-valve is in the
neutral position, the speed control does not affect
anything.
OIL RETURN
(RETURN)
OIL GALLERY
(PRESSURE)
SPOOL
VALVE
SOLENOID
PISTON
PILOT
PLUNGER
CHECK
VALVE
SPEED
CONTROL
BALL
VALVE
OIL LINE
OIL LINE
82206-105
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