The S12 valve is a three-way, two-position
spooled valve that switches hydraulic flow from the stack
valve to the screed lift cylinders. The valve is normally
open to allow oil flow to remain in the stack valve. When
the screed lift system is activated, S12 diverts flow from
the stack valve to the screed lift cylinders. When
deactivated, a coil spring returns the spool to the
normally-open position, allowing flow into the stack valve.
The valve has a nominal flow of 2.5 gal. (9,4 l)
per minute. Maximum internal leakage is 5.0 cubic
inches (81,9 ml) per minute.
The S13 valve is a two-way, pilot-operated
poppet valve that is normally closed. Opening the valve
allows oil from the screed lift cylinders to return to the
hydraulic reservoir, lowering the screed. When de-
energized, a coil spring closes the valve. Nominal flow
through the valve is 5.0 gal. (18,9 l) per minute. Internal
leakage is 0-5 drops per minute.
Eight identical four-way, two-position directional control
valves govern cylinder extend and retract functions. Left
and right screed extension and hopper lift cylinders are
each controlled by two valves. Each valve cartridge
spool is opened by an electric coil, and closed by a
spring. The valves have a nominal flow of 1.75 gal.
(6,62 l) per minute. Maximum internal leakage is 5.0
cubic inches (81,9 ml) per minute.
Relief valves are direct-acting, one-way poppet valves
that protect components from excessive hydraulic
pressure. Relief valves are located near track tensioning
cylinders, propulsion pumps, auxiliary pumps, propulsion
motors, auger/conveyor motors, and the stack valve
assembly. Relief valves are equipped with an adjusting
screw located underneath a hex head adjustment cap
nut. The adjustment increases or decreases spring
pressure on the internal valve, which changes the
pressure at which the valve opens. Relief valves are
closed until the adjusted pressure setting is exceeded.
When the pressure setting is exceeded, the relief valve
opens and excess oil flows through the return manifold
back to the hydraulic reservoir. Relief valves in the
paving machine have a nominal flow of 6.0 gal. (22,7 l)