TM 5-3820-241-34
Section III. HYDRAULIC CONTROL VALVE
3-21. General
a. The hydraulic control valve assembly is
mounted on the left side of the pedestal. It is
made up of five individual control valve sections
assembled in a bank and connected internally to
common pressure and return passages. Each
section contains a sliding spool with centering
springs and a check valve. The control valves are
used to direct oil flow for operating each of the
hydraulic cylinders. A relief valve is mounted at
the inlet port and set to open at 2500 psi to
protect the hydraulic components.
b. Each control system has two operating
positions and a neutral position. Each valve is
double acting; it directs the flow to and from
both cylinder- ports.
In the neutral of OFF
position, the spool lands block the cylinder ports
and the main pressure passage. Oil flow is blocked
at the valve and thereby prevents flow through
the system. However, when the valve spool is
shifted, oil is immmediately available for proper
operation.
c. When the spool is shifted in, flow is directed
over the check valve and through the pressure
chamber to the working port and to the cylinder
being operated. Oil returning from the cylinder
enters the opposite working port, passes through
the hollow center of the spool and through the
outlet to the oil reservoir. With the spool shifted
out, flow is directed through the working port.
The opposite port is open to the oil reservoir.
3-22. Hydraulic Control Valve Removal and
Disassembly
a. Removal.
(1) Block the drill b oom and feed mechanism
in a horizontal position.
(2) Loosen a hose connection at the control
valve and allow hydraulic oil to bleed into a
suitable container.
(3) Remove the hydraulic control valve in
numerical sequence as illustrated in figure 3-13.
3-19
