1.20 RELIEF VALVES

TM 5-3895-373-34 b. 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. c. 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. 1.20 RELIEF VALVES. 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) per minute. 1-11