Service Manual

Below is a cutaway of an actual hydraulic control

valve (Fig 10).

Here we see have a spool valve in our simple hydraulic

system, we can see that the valve is in the neutral posi-

tion and all the flow from the pump is directed back to

the reservoir.

If the spool is moved upward, the oil flow from the

pump is directed through the spool to one end of

the lift cylinder. The oil in the opposite end of the

cylinder is pushed out as the ram extends, and will

pass through the spool and return to the reser-

voir.(Fig 12).

Since the fluid from a positive displacement pump

must flow continuously whenever the pump is run-

ning it must have some where to go if not being

used by the actuators. If the load on the cylinder

becomes too great or if the ram bottoms out, the

flow from the pump will be directed past the relief

valve returning to the reservoir (Fig 13).

Substituting the lift cylinder with a gear motor, we

can now utilize out basic circuit to create rotational

movement to drive attachments (Fig 14).

Figure 12

Figure 10

Figure 11

Figure 13

Figure 14