System Description
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| Illustration 1 | g01230796 |
Location of the Control Valve (Steering, Decking Blade, and Priority Flow Control Valve) | |
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| Illustration 2 | g01222294 |
Control Valve (Steering, Decking Blade, and Priority Flow Control Valve) | |
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| Illustration 3 | g01222293 |
Control Valve (Steering, Decking Blade, and Priority Flow Control Valve) (1) Decking blade valve. (2) Steering control valve. (3) Priority flow control valve. (4) Port for secondary steering. (5) Relief valve for the priority flow control valve. | |
The control valve assembly is located on the firewall in front of the cab. Access is gained by removing the panel on the right side of the machine. The control valve assembly includes priority flow control valve (3), decking blade valve (1), and steering control valve (2). Relief valve (5) is part of priority flow control valve (3) .
Note: Port (4) is for the secondary steering arrangement.
Linkage rods connect steering control valve (2) to the steering wheel. As the operator turns the steering wheel, this causes the spool in steering control valve (2) to route oil to the steering cylinders.
The control lever for the decking blade activates solenoids on the decking blade valve. The solenoids allow pilot oil to flow to decking blade valve (1). The control lever of the decking blade controls the functions of the blade. The functions of the blade include lift, lower, and hold functions.
System Operation
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| Illustration 4 | g01222334 |
Priority, Steering, and Decking Blade Valve | |
The priority valve directs full pump flow to the brake hydraulic circuit in order to charge the accumulators for the brake system before any flow is directed to the other circuits. When the brake accumulators are charged, the priority valve directs pump oil flow to the steering system and the remaining hydraulic circuits.
The Illustration 4 shows the steering circuit ACTIVATED. No flow is available to the steering circuit until the brake accumulators are fully charged and the brake priority valve is shifted downward.
When the steering control valve is shifted upward, pump flow is directed through the top section of the brake priority valve to the flow compensator valve of the steering system. The pressure shifts the pressure compensator valve upward until the second section from the top is activated. The pump flow goes through the compensator valve to the steering control valve. The steering control valve directs pump flow to the steering cylinders.
The steering control valve also directs some of the pump flow through the loop at the lower side of the section and through the primary ball resolver to the top of the flow compensator valve. This pressure plus the spring force push down on the flow compensator valve. Flow through the compensator valve to the steering control valve is metered. The flow is equal to the steering system pressure minus the compensator spring. The signal pressure at the top of the flow compensator is directed through the secondary ball resolvers to the hydraulic pump. The load sensing pressure upstrokes the pump to the desired amount of flow that is needed to make a turn.
The flow compensator valve for the steering ensures that the steering system gets flow before any implements downstream get flow. As the flow demand decreases, the compensator valve is pushed up more in order to engage the third section in the compensator valve. This section directs most of the pump flow to the steering system and partial flow to the other hydraulic functions downstream of the steering system.
If the flow demand to the steering system decreases the lower section of the compensator valve is activated. This section directs most of the pump flow to the steering system.
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| Illustration 5 | g01222447 |
Priority, Steering, and Decking Blade Valve | |
When the blade control lever is moved to the BLADE RAISE position, solenoids shift the blade control valve downward in response to pilot oil. Pump system pressure flows through the center section of the flow compensator valve for the brake and through the upper section of the blade control valve to the rod end of the blade cylinders.
The pressure also makes a loop through the upper section of the blade control valve. The pressure goes to the top of the primary ball resolver. From the ball resolver, the pressure goes to the top of the flow compensator valve of the blade and through the series of ball resolvers to the hydraulic pump. This pressure signal upstrokes the hydraulic pump in order to increase flow.
If the pressure in the blade circuit increases to more than the pump system pressure, the flow compensator moves upward in order to block any additional flow from the pump to the blade circuit. In this position, blade drift is also minimal.