1.21. ELECTRICALLY CONTROLLED HYDRAULIC CIRCUITS

TM 5-3895-373-20 After the hydraulic oil exits the stack valve, the pressure is reduced by a 900 psi (6200 kPa) relief valve. The excess hydraulic oil is sent to the return manifold and back to the hydraulic reservoir. The reduced pressure fluid is passed through a check valve. The 900 psi (6200 kPa) hydraulic oil charges a hydraulic accumulator and maintains pressure to the track tensioning cylinders. When one or both tracks encounter an obstacle, the track tensioning cylinder is compressed, sending pressure pulsation’s into the track tensioning system. The pressure pulsation causes the check valve in the inlet of the track tensioning system to seat. This prevents the pressure pulsation from traveling to the rest of the hydraulic system. If the pulsation is small, it will be absorbed by the hydraulic accumulator. Larger pulses, which increase system pressure beyond 1800 psi (12 400 kPa), cause a relief valve to lift and vent excess pressure to the return manifold. 1.21. ELECTRICALLY CONTROLLED HYDRAULIC CIRCUITS. The paving machine uses electrically controlled hydraulic circuits for all hydraulic functions. Hydraulic pressure is supplied by two auxiliary pumps and an auxiliary vibration pump. Hydraulic functions controlled from the operator switch panel are: 1) Screed lift 2) Auger/conveyor drive 3) Extension screed positioning 4) Screed vibrator drive 5) Hopper wing lift Hydraulic functions controlled from the screed control panels are: 1) Auger/conveyor drive 2) Tow point lift 3) Extension screed positioning Auxiliary pumps and auxiliary vibration pump draw hydraulic oil from a common hydraulic reservoir. Pump output is routed through 50/50 flow dividers, pressure relief valves and flow control and solenoid valves. The flow control and solenoid valves control the speed of hydraulic cylinders and motors. Hydraulic oil return is routed to the return manifold. From the return manifold, the oil is forced through a hydraulic oil cooler and a return filter before returning to the hydraulic reservoir. Each individual function is explained in the following paragraphs. 1-41