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Figure 1-5. Mini-Valve in Neutral Position
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 determined
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.
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
functions use a 4-way (dual check valve) type
mini-valve.
Either type mini-valve is controlled by two pushing
type, electrically operated solenoids. The solenoids
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 depending 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 con-
trols in each 4-way mini-valve. They are needle
valve type controls which restrict the volume of oil
returning back into the reservoir, thereby controlling
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
OIL LINE
BALL
VALVE
OIL LINE
PILOT
PLUNGER
SOLENOID
PISTON
SPOOL
VALVE
OIL RETURN
(RETURN)
OIL GALLERY
(PRESSURE)
SPEED
CONTROL
CHECK
VALVE
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