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| Illustration 1 | g00454148 |
Control Levers (1) Bulldozer control lever (2) Grapple control lever | |
Bulldozer control lever (1) controls the bulldozer lift control section, the bulldozer tilt control section and the bulldozer angle control section of the bulldozer control valve. Grapple control lever (2) operates a hydraulic pilot valve which controls the operations of the main control valve for the grapple. The bulldozer control lever is connected to the control valve by a mechanical linkage. The grapple control levers are connected to the main control valve for the grapple by pilot pressure and electronic switches.
Bulldozer Control Valve
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| Illustration 2 | g00454149 |
Three valve bank for PAT Bulldozer (A) Bulldozer angle control section (B) Bulldozer tilt control section (C) Bulldozer lift control section (D) Inlet manifold (E) End cover | |
Pressure compensated control valves (A) , (B) and (C) are held together with inlet manifold (D) and cover (E) in order to form the three valve bank for the PAT bulldozer. This control valve bank controls the operations of the bulldozer. Each control valve has a signal passage that is connected with each port. Each control valve has two resolver valves. The primary resolver compares the pressures of the two work ports in each valve section. The secondary resolver compares the section's highest resolved pressure to the highest resolved pressure from the previous section. These secondary resolvers are connected in order to resolve the highest pressure that is required in the control valve bank. This highest resolved pressure is sent to the hydraulic pump in the form of an oil pressure signal. When the control valves are in the HOLD position, the signal pressure is drained to the tank. This allows the pump pressure to decrease to the standby pressure. See Systems Operation, "Signal Resolver Network" for more information.
The bulldozer control valve is located in the operator's compartment to the right of the seat. Linkage rods connect the valve sections to the operator control levers.
The sections of the control valve are held together by three tie rods and nuts. O-rings are use between the control valves. Pump pressure is seen by all valves in parallel.
All sections have manual actuation. All sections have closed centered directional stems. The tilt valve stem has three positions: EXTEND, HOLD and RETRACT. The valve stem for the bulldozer angle section has three positions: ANGLE LEFT, HOLD and ANGLE RIGHT. The valve stem for the lift section has four positions: RAISE, HOLD, LOWER and FLOAT .
The lift section has a makeup valve in order to reduce pause time. The pause time is caused by the weight of the blade that forces the oil out of the rod end. The pump cannot fill the head end of the lift cylinders at a quick enough rate. The bulldozer angle section has two combination line relief and makeup valves in order to protect the angle cylinder. See Systems Operation, "Line Relief and Makeup Valve" for more information.
All sections have load check valves in order to prevent backflow when the pump pressure is less than the work port pressure. This prevents unwanted blade movement (droop) as the stem is shifted.
Grapple Control
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| Illustration 3 | g00454150 |
Fixed Boom Grapple Control Valve (1) Grapple rotator (2) Grapple tong (3) Boom (4) Cover (5) Inlet cover (6) Tank port (7) Signal port (8) Inlet port | |
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| Illustration 4 | g00454151 |
Swing Boom Grapple Control Valve (1) Grapple rotate control valve (2) Grapple tong control valve (3) Main boom and Jib boom control valve (4) Cover (5) Inlet cover (6) Tank port (7) Signal port (8) Inlet port (9) Swing control valve | |
The control valve is located in the mounting structure for the boom on machines that are equipped with a swing boom. The control valve is mounted to the boom on machines that are equipped with a fixed boom. Standard equipment includes the following components: grapple rotate control valve (1), grapple tong control valve (2), cover (4) and Inlet cover (5) . Fixed boom machines have one boom valve (3) in order to control the boom. Machines that are equipped with swing booms have two boom control valves (3) for both sections of the swing boom and swing valve section (9) in order to control the sideways movement of the boom.
Inlet cover (5) is bolted to boom control valve section (3) . Inlet port (8) , signal port (7) and tank port (6) are part of the inlet cover. Main system oil flows from the bulldozer control valve through lines to inlet port (8) .
Resolver signal oil flows from port (7) through lines to the bulldozer control valve. This pressure is compared with the highest resolved pressure from the bulldozer valve. The higher pressure of the two is sent to the hydraulic pump. Return oil flows from port (6) through the bulldozer valve to the tank.