Alamo MACHETE Product Service Manual page 33

CONTROL VALVE - LOAD SENSING
ENGINE RUNNING AND VALVE FUNCTION ACTIVATED: (See Figure 16)
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 takes place. The Shifting of the Spool opens a passage to
connect one end of the selected Cylinder to Pressure ("P") Galley and connect the other end to the
Return ("T") Galley. The Shifting Spool also connects the Load Sense Circuit to the Pressure ("P")
Circuit. The Pressure Signal is sent to the Pump Control System, which increases the Oil Flow to the
Control valve. The Pressure present in the ("P") circuit and the Load Sense Circuit is the same
and is created by the Load on the Cylinder. (NOTE: The Load Sense Signal Shown in Figure
16 is an internal passage in Valve, it is shown here on the outside for illustration onlr and
cannot be seen if actually looking at valve).
Before the Pressurized Oil reaches the Flow Control Spool, it must first pass through the
Segment Compensation Spool. The Compensating Spool uses Load Sense and Spring Pressure
to maintain constant pressure drop across the Main spool, Both when the Load changes and when
a Segment with a higher load pressure is activated.
The maximum Pressure in the Swing, Lift and Dipper Circuits is controlled by the settings of
the Work Port Relief Valves of these Circuits. These Settings may be different for opposite ends of
the same Cylinder or Circuit. The Cartridge also incorporates 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
whenever there is no more Oil being demanded by a Cylinder than is supplied (Such as with the
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 (Tilt and Door Functions DO NOT have Proportional
Control, they are "Open" or "Closed" only). 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 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 actuation of the
Cylinders.
The Tilt and Door Functions (While not Proportionally Controlled) are controlled by Pilot Oil
Control Valves. However instead of opening or closing based on the Joystick position, these valves
will fully Open (or Close) when activated.
When the Function is returned to Neutral at the Joystick, The electrical current to the Valve
Controller is stopped. Therefore 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 Neutral (Centered) position. When the Spool is centered, The Load Sense Circuit is connected
to the Tank ("T") Galley. With no Load Sense Signal, Pump returns to minimum.
MACHETE (Service Manual) 04/04
© 2004 Alamo Group Inc.
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