1.21.6. Screed Extension System

TM 5-3895-373-20 1.21.6. Screed Extension System. The screed 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 header. 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 hydraulic reservoir. 1-52