The shearer height adjustment system is generally hydraulic. The hydraulic system has single pump and double gear pump. The oil circuit system can be simplified as the main oil circuit, control oil circuit, and brake oil circuit. The main oil circuit controls two hydraulics. The cylinder lifting rocker arm requires a larger flow rate, and the required larger oil pressure is slightly lower than that of the high pressure relief valve. The control oil circuit only controls the action of the hand-hydraulic reversing net. The required flow rate is small. The brake oil circuit uses oil to compress the brake pads to achieve braking efficiency. The same requires a small flow rate. The required oil pressure of the oil circuit is about 2MPa. . This article compares hydraulic systems.

1. Fuel tank heat dissipation:

When the hydraulic oil passes through the mesh block, due to the presence of elbows, joints, mesh openings, and sudden changes in cross-sections, the flow or direction of the flow changes in speed, resulting in flow resistance in local areas, resulting in pressure loss, and increasing oil temperature.

In the principle of the dual gear pump system, the main oil route has no pressure drop, and the power waste is mainly in the control oil route. From the calculation results, in order to meet the heat dissipation requirements of the fuel tank, the fuel tank of the single pump configuration is larger than the fuel tank of the double pump, which is disadvantageous to the design of the shearer requiring a short body.

2. Control valve life:

In a single-pump hydraulic system, the oil from the main oil circuit enters the control oil circuit as a whole, and the flow is relatively large, so a thicker hydraulic pipe must be used in the control. At the same time, during control, the oil passes through more small holes and the pressure loss is more serious. The large flow also means that more impurities may enter the control oil circuit along with the liquid flow, which is likely to cause blockage of the electromagnetic reversing network or pipeline, and cause shutdown and maintenance accidents. In the double 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 a fine filter to ensure the quality of the oil, which greatly reduces the occurrence of hydraulic system failures.

3. Power loss:

The oil passes through the middle position (H) of the left and right rocker arm hydraulic cylinder net group through the pump, and then enters the control oil circuit. When it is not in operation, it does not pass through the electromagnetic reversing net and returns to the oil tank through a low pressure overflow net (2MPa). There is a high-pressure overflow net (20MPa) at the outlet of the oil pump. When the height is adjusted, the oil first enters the oil cylinder and then enters the control oil circuit. When the pump is working at full load (ie, the outlet oil pressure is 20MPa), the oil pressure supplied by the hydraulic pump to the hydraulic cylinder is 18MPa, which shows a 10% power waste.

This problem does not exist in the double gear pump system. When the height of the main pump is not adjusted, the oil of the main pump is directly returned to the oil tank after passing through the neutral position (H) of the left and right rocker arm hydraulic cylinder net group. The control system is only controlled by a 4mLhr small hydraulic pump, and there is a low pressure overflow network (2MPa) in the control oil circuit to ensure the oil pressure of the control system and the brake system. When the height is adjusted, the main pump oil passes through the hydraulic cylinder, and the remaining oil is connected to the oil tank. At full load, the pressure drop is the high-pressure overflow set pressure (20MPa). It can be seen that there is no problem of power waste in this system.

From the above analysis, it can be seen that the application of the double gear pump system in the shearer height adjustment system can significantly reduce power waste, reduce oil temperature rise, shorten the length of the machine body, and increase the life of hydraulic components.