Alamo MACHETE Product Service Manual page 37

CONTROL VALVE - FIXED DISPLACEMENT
ENGINE RUNNING AND VALVE FUNCTION ACTIVATED: (See Figure 18)
When a function is selected and actuated by the Controller, The Proportional Control
System directs the Pilot Pressure Oil to move the Main Spool in its bore. Two actions resulting from
the Main Spool Shifting in its bore now take place. The Shifting Spool opens a Passage to connect
one end of the selected Cylinder to the Pressure ("P) Galley and connect the other end to the Return
("T") Galley. The Shifting Spool also allows the Load Signal created by gravity acting on the Cylinder
to connect to the Spring end of the Pressure Bypass Adjusting Spool. This acts with the Spools
spring to close the Passage to the Tank ("T"), and allows the correct amount of Oil to travel to the
Cylinders. Based on the Load Sense Pressure, The Pressure Bypass Adjustment Spool will allow
only the Oil needed at the Cylinder in accordance with the Controllers Position. Any excess Oil will
be allowed to return to Tank ("T"). The Pressure present in the ("P") Circuit and the Load Sense
Circuit is the same and is created by the Load on the Cylinder.
Before the Pressurized Oil reaches the Flow Control Main Spool, It must first pass through
the Segment Compensation Spool, this Spool maintains a constant pressure differential (Flow)
between the Supply Pressure and the Cylinder Pressure at the Flow Control Main Spool. (Simple
Explanation: Function of Segment Spool is to keep a constant even pressure to Main Spool so
Cylinder cannot suck in Air).
The maximum Pressure in the Swing, Lift and Dipper Circuits is controlled by the settings
of the Work Port Relief Valves for these Circuits. These settings may be different for opposite ends
of the same Cylinder or Circuit. The Cartridge also incorporate Anti - Cavitation Check Valves to
provide make up Oil if required. These Valves will open to allow Oil from the tank Galley to enter the
Cylinder when ever there is no more Oil being demanded by a Cylinder than is supplied (Such as
with Lowering function) in order to prevent Cavitation.
Proportional Control of the Lift, Dipper and Swing Functions is achieved through the
Proportional Control System of each section. When an electrical signal is sent from the Joystick
to the Electric Controller in the Valve, The Pilot Pressured Oil is then allowed to flow to either end
of the Spool thus causing it to shift. The amount of Pilot Pressured Oil to either end of Spool is varied
with the Pilot Oil Control Valve by the Electric Controller there by controlling the distance the Spool
Shifts. This in turn controls the volume of Oil sent to the Cylinders and consequently, the Speed of
activation of the Cylinders.
The Tilt and Door Function, While not proportionally controlled are controlled by Pilot Oil
Control Valves. However instead of opening or closing based on Joystick Position, These Valve will
fully open or fully closed when activated, Tilt and Door Functional are not proportional they are open
full or closed full only.
When the Function is returned to Neutral at the Joystick, The Electrical current to the Valve
Controller is stopped. There fore the Pilot Oil Control Valves return to their normal positions and the
Flow of Pilot Pressure Oil to the Main Spool is stopped. The Springs on the Main Spool returns the
Spool to its centered (Neutral) Position. When the Spool is centered the Load Sense Signal stops.
With no Load Sense Signal present the Pressure Bypass Adjustment Spool allows most of the Oil
in the Pressure ("P") Port to return to the Tank ("T"). The Pilot Reducing Valve retains Pilot (Standby)
Pressure in the Valve.
MACHETE (Service Manual) 04/04
© 2004 Alamo Group Inc.
37