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| Illustration 1 | g03713786 |
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(1) Tank return passage
(2) Makeup valve (3) Work port passage (4) Work port passage (5) Relief valve (6) Tank return passage (7) Dead engine lower screw | |
The tractor has three makeup valves. There is two makeup valves in the head end of the bulldozer lift valve. There is one makeup valve in the head end of the ripper valve.
The makeup valves helps prevent voiding of the cylinder.
Voiding of the cylinder can occur when the pressure in work port passage (3) is lower than the pressure in tank return passage (1).
The pressure in tank return passage (1) causes poppet of makeup valve (2) to move to the right because the return oil pressure is higher than the work port pressure. The pressure is maintained in tank return passage (1) by a check valve in the return to tank line.
When poppet of makeup valve (2) moves to the right, the valve opens. The return oil pressure can flow past makeup valve (2) into work port passage (3). This return oil mixes with pump oil in order to help prevent voiding of the cylinder.
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| Illustration 2 | g03713786 |
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(1) Tank return passage
(2) Makeup valve (3) Work port passage (4) Work port passage (5) Relief valve (6) Tank return passage (7) Dead engine lower screw | |
The line relief valve is a pilot type valve.
The line relief valve protects the cylinders and the lines from high pressure.
The tractor has at least two line relief valves. There is one line relief valve in the rod end of the bulldozer lift valve. There is one line relief valve in the rod end of the ripper valve.
The tractor has four line relief vales if the tractor is equipped with the optional angle valve. There is one line relief valve in the rod end of the bulldozer lift valve and the rod end of the ripper valve. There are two line relief valves in the angle valve.
The oil acts against relief valve (5). If the oil pressure in work port passage (4) is less than the setting for the line relief valve, the force of the spring in the valve will hold relief valve (5) in the closed position.
When the force from the pressure in work port passage (4) is more than the force of the spring, poppet of valve (5) moves to the left. Causing path to tank return passage (6) open. Oil flows past relief valve (5) to the hydraulic tank.
Relief valve (5) remains open, if the pressure of the oil that is in work port (4) is above the setting for the line relief valve.
The relief valve in the control valve for blade lift in illustration 2 is different from the other relief valves. In addition to being a relief valve, the valve also has dead engine lower screw (7). The screw can be turned in order to push central pin of valve (5) to open the passage between work port passage (4) and tank return passage (6).