Hydraulic drive arrangements

1,012,975. Hydraulic transmissions. VSESOUZNY NAUCHNO - ISSLEDOVATELSKY INSTITUTE STROITELNOVO I DOROZHNOVO MASHINOSTROENIYA. Aug. 12, 1963, No. 31704/63. Headings F2C and F2D. In a hydrostatic transmission for slewing a crane wherein a pump 1 supplies pressure liquid to a motor 3 through a valve 26, an accumulator 5 is connected through a shut-off valve 21 to the high-pressure line to store energy during motor reversal and an accumulator 6 which is maintained one-third full by a make-up pump 2 is provided in the low-pressure line 34. The speed of the motor 3 is, as shown, controlled by a manually operated by-pass valve 33, but may additionally be controlled by providing a variable displacement pump 1. When the accumulator 6 is one-third full it closes a switch 8 to energize a solenoid operated valve 10 which opens a valve 12 to connect the delivery of the pump 2 to the reservoir. A switch 7, which is closed when the accumulator 5 is full, energizes a solenoid-operated valve 9 which opens a bypass valve 11. The five position control valve 26 has a central motor braking position in which the motor draws liquid from the low-pressure accumulator 6 through one-way valves 24 and discharges through one-way valves 25 to the high-pressure accumulator 5. Two intermediate idle positions in which the motor draws from and discharges to the accumulator 6 and extreme end forward and reverse drive positions. When use of the accumulator 5 is not required, valves 21, 22, 23 are closed. When the valve 22 is closed overrun of the motor 3 is prevented by a valve 29 which closes to block the motor outlet when the motor outlet pressure exceeds the inlet pressure. A filter 4 is provided in the circuit and high-pressure relief valves 27, 28 between the low and highpressure motor lines prevent excess pressure in the circuit. The accumulators 5, 6 are provided with pressure gauges 13, 14 and drain cocks 17, 18.