TM 5-3820-241-34
Section III. HYDRAULIC CONTROL VALVE
c. When the spool is shifted in, flow is directed
3-21. General
over the check valve and through the pressure
a. The hydraulic control valve assembly is
chamber to the working port and to the cylinder
mounted on the left side of the pedestal. It is
being operated. Oil returning from the cylinder
made up of five individual control valve sections
enters the opposite working port, passes through
assembled in a bank and connected internally to
the hollow center of the spool and through the
common pressure and return passages. Each
outlet to the oil reservoir. With the spool shifted
section contains a sliding spool with centering
out, flow is directed through the working port.
springs and a check valve. The control valves are
The opposite port is open to the oil reservoir.
used to direct oil flow for operating each of the
hydraulic cylinders. A relief valve is mounted at
3-22. Hydraulic Control Valve Removal and
the inlet port and set to open at 2500 psi to
Disassembly
protect the hydraulic components.
a. Removal.
b. Each control system has two operating
(1) Block the drill b oom and feed mechanism
positions and a neutral position. Each valve is
in a horizontal position.
double acting; it directs the flow to and from
(2) Loosen a hose connection at the control
both cylinder- ports. I n t h e n e u t r a l o f O F F
v a l v e and allow hydraulic oil to bleed into a
position, the spool lands block the cylinder ports
suitable container.
and the main pressure passage. Oil flow is blocked
(3) Remove the hydraulic control valve in
at the valve and thereby prevents flow through
numerical sequence as illustrated in figure 3-13.
the system. However, when the valve spool is
shifted, oil is immmediately available for proper
operation.