![]() ![]() The pressure on each of these paths push on opposite sides of the flow divider spool. The oil that goes through the needle valve will continue on to the C port. The oil going into the flow divider spool can only go to the left towards the A port. As oil comes in port B, some oil goes through a needle valve on the right (#5) and some goes to the center land on the flow divider spool (#3). In the middle of the valve is a flow divider. There is another check valve (#16) on port C, and a spring loaded spool (#4) to block the flow on port D. The two ports on the bottom (C and D) are plumbed in parallel with the bucket tilt cylinders. When you raise the main boom, the check valve is closed and oil has to flow from B to A through the other parts of the circuit. When you lower the main boom, oil flows through the check valve from A to B, bypassing the rest of the circuit. Notice that directly between these two ports is a check valve (#16) being held down by a spring (#18). The two ports on the top (A and B) are plumbed in series with the main boom lift cylinders. The next picture is an internal schematic of what is going on in this valve block. ![]() This picture shows what parts go inside the valve. The self-leveling valve is in the bottom right corner. The diagram below shows how the valve connects to the bucket tilt cylinders. In order to determine why it was leaking, I first had to figure out how it worked. This magical block of steel had 4 hydraulic lines connected to it and ports all around the sides. ![]() I isolated the problem to being inside the self-leveling valve. I bought a Mustang skid steer that had a problem: the bucket would leak down. This is particularly handy when you need the load to remain level such as when using pallet forks, but it is also nice with a bucket of material so it doesn’t spill over the back of the bucket when raising the boom. The basic concept is that when you raise the main boom, the bucket is tilted down to keep it level with the ground rather than locked to the main boom. Many loaders have a self-leveling valve for the boom lift and bucket tilt hydraulic circuits. Articles / How a hydraulic self-leveling valve works ![]()
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