DIPSTICK 4646347 - Caterpillar

Makeup Valve Operation
Illustration 1 g01764658
(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 screwThe makeup valve 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 makeup valve (2) to move to the left 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 makeup valve (2) moves to the left, 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.Line Relief Valve
Illustration 2 g01764658
(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 screwThe 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 three line relief valves. There is one line relief valve in the rod end of the bulldozer lift valve. There are two line relief valves in the angle valve.If the tractor is equipped with a ripper, there will also be a fourth line relief valve in the rod end of the ripper 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, valve (5) moves to the right. This opens a path to tank return passage (6). 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 open the passage between work port passage (4) and tank return passage (6) .