Alamo MACHETE Product Service Manual page 35

CONTROL VALVE - FIXED DISPLACEMENT
GENERAL INFORMATION: Fixed Displacement Valve
The "Fixed Displacement" (Open Centered) Systems Control Valve is designed to be
used on tractors that DO NOT have Load Sense (Closed Centered) Hydraulic Systems.
ENGINE RUNNING AND ALL FLOW CONTROL VALVES CENTERED:
(See Figure 17)
Oil from the Pump enters the Control Valve at the "P" (Pressure) Port on the Inlet Section
(End Cap), If there are no other Hydraulic functions being used; all of the flow from the Fixed
Displacement Pump must go through the Control Valve. The Flow of Oil is blocked by the Flow
Control Spools in each Valve Section, The Main Relief Valve, The Proportional Control System
valves, The Load Sense Passage Plug and the Bypass Adjustment Valve. The first Circuit to
be charged is the Pilot Circuit, Oil passes through the Pilot Reducing Cartridge which limits the
Pressure in the Circuit to approximately 200 PSI.
After the Pilot Circuit is charged, Additional Oil being pumped into the Valve increases
the pressure in the pressure ("P") Circuit. When in Neutral, The Pressure in the pressure ("P")
Circuit is limited to approximately 215 PSI by the Pressure Bypass Adjustment Valve Spring.
When the Pressure in the ("P") circuit is enough to overcome the force of the Bypass Spring,
the Bypass Spool is shifted in its bore, Opening a passage between the Pump Oil ("P") Circuit
and the Return ("T") Circuit. The Bypass Spool maintains enough pressure (Pilot Pressure) in
the System to actuate the Flow Control Spools and returns any surplus Oil to Tank.
When the Flow Control Spools are centered (Neutral), the Load Sense Passage works in
conjunction with the Bypass Spring to limit the Main System Pressure in Circuit ("P"). Since
there is no pressure in the Load Sense Passage in Neutral (Centered) the force of the Spring
is the only factor determining System Pressure.
NOTE: The Load Sense Passage shown in figure 17 is an internal passage inside of Valve and
cannot be seen if looking at Valve, It is shown here outside Valve as Illustration Only.
MACHETE (Service Manual) 04/04
© 2004 Alamo Group Inc.
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