1.21.6. Screed Extension System. The
extension system consists of control switches on
operator switch panel and left and right screed control
panels, right auxiliary hydraulic pump, 500 flow divider,
solenoid valve and hydraulic cylinders. Since the left and
right screed extension systems are identical, the
following applies to either screed extension system.
Power for the screed extension system originates at
CB5. The operator switch panel has switches for both
left and right screed extension cylinder control. The left
screed control panel controls the left screed extension
cylinder while the right screed control panel controls the
right screed extension cylinder. Power through the
spring loaded center OFF switches is directed to the
extend or retract solenoid valves and to the power
beyond solenoid valve.
Hydraulic oil for the screed extension system is supplied
from the right auxiliary hydraulic pump. The right
auxiliary hydraulic pump contains two pumps, 0.7 and
0.58 cu in.
(11,5 and 9,5 cc) outputs, mounted on a common shaft.
The 0.58 cu in. (9,5 cc) output pump supplies oil to a
50/50 flow divider. The flow divider splits the hydraulic
flow, sending half to the tow point and screed vibration
systems and half to the stack valve.
Stack valve pressure is regulated at 2500 psi (17 238
kPa) by a pressure relief valve internal to the stack valve.
This pressure can be read at the test manifold. The
relief valve ports excess hydraulic oil to the return
manifold and back to the hydraulic reservoir.
The oil that is not routed through the relief valve is routed
to the power beyond valve. In the normal, deenergized
position, the power beyond valve routes all hydraulic oil
out of the stack valve and to the track tensioning system.
The power beyond solenoid energizes whenever any
hydraulic function on the stack valve is operated except
when screed is allowed to float on top of paving material
during operation. When the power beyond valve
solenoid is energized, the valve shifts and does not allow
any oil to leave the stack valve by way of the track
tensioning system. All hydraulic oil entering the stack
valve is therefore directed to the screed lift valve. This
temporarily prevents hydraulic oil from flowing to the
track tensioning system.
The screed lift valve is normally deenergized, allowing all
hydraulic oil to flow to the stack valve supply header.
When the screed lift system is in use, the screed lift
valve is energized, redirecting all hydraulic flow from the
stack valve to the screed lift system. Since this prevents
any hydraulic oil from entering the stack valve supply
header, no stack valve functions will operate until the
screed lift valve is deenergized. Once hydraulic oil is past
the screed lift valve, the oil enters the stack valve supply
When an extension screed control switch is activated,
the extend solenoid or the retract solenoid will energize,
repositioning the valve. The valve will allow the hydraulic
oil from the stack valve supply header to move the
cylinder in the , selected direction. The hydraulic oil
forced out of the cylinder is directed to the stack valve
return header. The stack valve return header directs the
hydraulic oil to the return manifold and then to the