Alamo MACHETE Product Service Manual page 31

CONTROL VALVE - LOAD SENSING
GENERAL INFORMATION: Load Sensing Valve
The "Load Sensing" (Closed Centered) Systems are Commonly used on Tractors that
may employ either Fixed Displacement or Variable Displacement Pumps.
The Load Sense Feature may control Pump Output or in the case of the Fixed
Displacement Pump, Simply control delivery to the control Valve returning surplus Oil to the
tank.
The Goal of either System is to reduce wasted energy, wear and tear from pumping Oil
under Pressure when there is no demand on the system.
For the Purposes of this Manual, A Load Sense System will be defined as any system
that varies the Flow of Oil to Control Valve based on a demand signal sent through a separate
Load Sense Circuit, Closed Center System may or may not be load sensing systems.
ENGINE RUNNING AND ALL FLOW CONTROL VALVES CENTERED:
(See Figure 15)
Oil from the Pump enters the Control Valve at the "P" (Pressure) Port on the Inlet Section
(End Cap) and is available at each Flow Control Spool, The Pilot Reducing Cartridge and the
Main Relief Valve. Oil flow is blocked by the Flow Control Spools, The Proportional Control
System Valves and the Main Relief Valves.
Pressure at Neutral will normally be referred to a "Standby Pressure" and will be at least
200 to 250 PSI in order to maintain Pilot Pressure. Oil passes through the Pilot Reducing
Cartridge and is blocked at each Proportional Control Valve. The Pilot Reducing Valve maintains
200 to 250 PSI in the Pilot Circuit.
The Main Relief is located in the Inlet Section (End Cap) of the Valve and limits the
Pressure in the "P" Port to a maximum 2700 PSI.
The Load Sense Circuit is connected to the Return "T" Circuit when all Spools are in the
Neutral (centered) Position.
With the Flow Control spools in their Neutral (centered) position, Oil Flows to and from
the Cylinder is blocked by the Spool. The centering of the Spool connects the Load Sense circuit
to the Return "T" Galley in the Control Valve. Since there is no Load Sense Signal being sent to
the Pump, The Pump only delivers enough Oil to maintain Pilot Pressure.
MACHETE (Service Manual) 04/04
© 2004 Alamo Group Inc.
31