Terex TS14G, Maintenance Manual

Page: 260 / 376

Section 235-0160
Bowl Hydraulic System - Servo Control Valve
SM 1775 3-99
2
REMOVAL
WARNING
To prevent personal injury and property
damage, be sure wheel blocks, blocking
materials and lifting equipment are properly
secured and of adequate capacity to do the job
safely.
1. Position the vehicle in a level work area, apply the
parking brake and switch off the engine. Operate the
steering in both directions several times to relieve
any pressure in the steering system.
2. Place the battery master switch in the 'Off' position
and block all road wheels.
3. Remove screws and washers securing cover to
right hand side dash panel.
4. Identify and tag all nylon control lines connected to
servo control valve, to aid in 'Installation'.
5. With suitable container available to catch spillage,
disconnect nylon control lines from servo control
valve. Drain the oil from the lines into the container.
Cap lines and valve ports to prevent ingress of dirt.
6. Remove mounting hardware securing servo control
valve to its mounting on right hand dash panel. Lift
valve out from dash panel and remove to a clean
area for disassembly.
DISASSEMBLY
Numbers in parentheses refer to Figs. 1 & 2.
WARNING
Spring loaded parts. Use care when removing
end cap, retainers and plugs to prevent
sudden release of spring tension behind these
parts. Personal injury or property damage
could result if care is not taken.
Note: Clean entire servo control valve assembly with
a suitable solvent and dry thoroughly prior to
disassembly.
1. Remove caps from valve housing (19) ports.
2. If required, clamp servo control valve assembly in
a soft jawed vice. Take care to avoid damaging valve
housing (19) machined surfaces.
DESCRIPTION
The servo control valve is mechanically actuated
spool type valve controlling and directing signal oil
pressure supplied by the main control valve. The
valve spools are operated by levers connected to the
spool ends. Operation of control levers moves the
spools to open and close the inlet port to the signal
ports to control movement of the valve spools.
Good control of the main hydraulic valve spools is
attained by matching the pressure gain through the
servo valve to the resistance of the main hydraulic
control valve spool centering springs. As the servo
valve spool is shifted from neutral, some signal oil is
directed to the appropriate main hydraulic control
valve spool, and some oil is directed back to the tank
from the other side of the spool. As the servo valve
spool is shifted farther through its stroke, so more oil
is directed to the main hydraulic control valve spool,
moving it farther through its stroke in direct
proportion to the servo valve spool movement.
The ejector and apron spools have a mechanical
detent in the lower position.
OPERATION
Neutral
When the levers are in the neutral position, the
spools are held in the centered positions by centering
springs. The lands on the valve spools block ports A,
B, C, D, E and F from the oil inlet, and since this
valve is a closed centre component, excess oil
pressure goes over the relief valve, and back to the
tank.
Raising and Lowering
When any lever is moved to the raise position, the
attached valve spool is moved downwards and oil will
flow through ports B, D and F to stroke the respective
main hydraulic control valve spool. Oil on the other
side of the main hydraulic control valve is displaced
through nylon tubing back to the servo valve and
through ports A, C and E back to tank.
In the lower position, oil will flow through ports B, D
or F when the attached spool is moved upwards. This
action will stroke the respective spool to give a lower
condition.
Courtesy of Machine.Market