Loader Valve - Variable Flow
Shuttle Valve Signal Network
Each control valve section has two shuttle valves. Each valve
compares two pressure signals. One of the shuttles is the
primary 18 and the other is the secondary 17.
The primary shuttle 18 compares the pressure signal
between the two service ports A and B in each valve section,
the head and the rod pressure of the cylinder. In the example
shown the boom service 37 port B pressure signal is greater
than port A. Primary shuttle 18 moves across, the pressure
signal is the highest shuttle pressure. This signal pressure
passes to the next shuttle.
The secondary shuttle operates the same as the primary
shuttle but compares pressure signals between valve
sections.
The signal network is arranged in series. It starts at loader
valve block 9 inlet section which is connected to the steer
valve 45. The last secondary shuttle in the loader valve block
is connected to the first secondary shuttle in the backhoe
valve block 25. The highest shuttle signal pressure from the
loader valve block goes to the backhoe valve block.
The highest shuttle signal pressure is felt at the hydraulic
pump which instructs the pump to vary the output to meet
the highest shuttle load requirement. The stand-by pressure
spool in the pump adds margin pressure to the load
requirement. The single highest shuttle signal pressure plus
margin pressure governs pump output.
The pump will not change output until the shuttle network
identifies a different shuttle signal.
7 - 7
Section E
Hydraulics
9803/3280
Section E
7 - 7
Issue 1
Circuit Descriptions
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