The height adjustment system of shearer is generally hydraulic height adjustment. The hydraulic system has single pump and double gear pump. The oil circuit system can be simplified as main oil circuit, control oil circuit and brake oil circuit. The common main oil circuit controls the lifting rocker arm of two hydraulic cylinders. The required flow is large, and the required oil pressure is slightly less than the oil pressure of high-pressure relief valve. The control oil circuit only controls the action of the hand hydraulic steering net, which requires less flow. The brake oil circuit uses oil to compress the brake pads to achieve braking efficiency. Similarly, the flow is small, and the oil pressure required by the oil circuit is about 2MPa. This paper compares the hydraulic system.

1. Heat dissipation of oil tank:

When the hydraulic oil passes through the mesh block, due to the existence of elbows, joints, mesh openings and sudden changes in cross-section, the flow resistance will be generated in the local area due to the speed change of flow or flow direction, resulting in pressure loss and oil temperature rise.

In the principle of double gear pump system, the main oil circuit has no pressure drop, so the power waste is mainly in the control oil circuit. From the calculation results, in order to meet the heat dissipation requirements of the oil tank, the oil tank of single pump configuration is larger than that of double pump configuration, which is unfavorable to the design of shearer with short fuselage.

2. Control valve life:

In the single pump hydraulic system, the oil in the main oil circuit enters the control oil circuit as a whole, and the flow is large, so a thicker hydraulic pipe must be used in the control. At the same time, in the control, the oil through more holes, pressure loss is more serious. At the same time, large flow also means that more impurities may enter the control oil circuit with the liquid flow, which is easy to cause the blockage of electromagnetic reversing network or pipeline, resulting in shutdown maintenance accidents. In the dual pump system, because the control oil circuit is a relatively separate circuit, the small pump sucks oil through the main oil return pipe, enters the pump body, and passes through the fine filter to ensure the quality of the oil and greatly reduce the occurrence of hydraulic system faults.