TM 5-2410-240-23-1
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IMPLEMENT HYDRAULIC SYSTEM CONTINUED
Line Relief and Makeup Valve
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1. Makeup Valve
Makeup valve (Figure 13, Item 1) helps prevent voiding of the cylinder. Voiding of the cylinder can occur when the
pressure in the work port passage (Figure 13, Item 3) is lower than the pressure in the tank return passage
(Figure 13, Item 2).
The pressure in the tank return passage (Figure 13, Item 2) causes the makeup valve (Figure 13, Item 1) to move
to the left because the return oil pressure is higher than the pump oil pressure. A check valve in the return to the
tank line maintains pressure in the tank return passage.
When the makeup valve (Figure 13, Item 1) moves to the left, it opens, and the return oil flows past the valve and
into the work port passage (Figure 13, Item 3). This return oil mixes with pump oil in order to help prevent voiding of
the cylinder.
2. Line Relief Valve
The line relief valve (Figure 13, Item 5) is a pilot type valve. It protects the cylinders and the lines from high
pressure. There is one line relief valve in the rod end of the blade raise control valve and two in the blade angle
control valve. There is also a line relief valve in the rod end of the ripper control valve (D6K with Ripper).
Oil acts against the line relief valve (Figure 13, Item 5). If the oil pressure in the work port passage (Figure 13,
Item 4) is less than the current line relief valve setting, the force of the spring in the valve holds the line relief valve
in the closed position.
When the force from pressure in the work port passage (Figure 13, Item 4) is more than the force of the spring, the
line relief valve (Figure 13, Item 5) moves to the right. This opens a path to the tank return passage (Figure 13,
Item 6), and oil flows past the line relief valve to the hydraulic tank.
The line relief valve (Figure 13, Item 5) remains open if the oil pressure in the work port (Figure 13, Item 4) is
greater than the current line relief valve setting.
The line relief valve (Figure 13, Item 5) in the blade raise control valve is different from the line relief valves in the
other control valves. In addition to being a relief valve, it also contains the dead engine LOWER screw (Figure 13,
Item 7).
Figure 13. Line Relief and Makeup Valve.
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