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In the oil circuit of the hydraulic system, when the inclined axis and swash plate axial piston pumps are used at the rated speed or exceed the rated speed, the oil inlet of the pump must be filled with oil under pressure to ensure that the oil inlet pressure of the hydraulic pump is 0.2- 0.4MPa, that is to say, a low pressure charge pump is needed to supply oil, and its flow should be more than 120% of the main pump flow. When used at reduced speed, the oil inlet allows self-priming.
There are two oil drain holes on the casing of the inclined axis type and swash plate type axial piston pump, which are used for oil drainage and cooling. The usage methods are as follows:
1. Connect a drain hole at the height of the hydraulic cylinder to the oil pipe before use, so that the leaking oil in the shell can flow back to the oil tank smoothly. For hydraulic pumps with manual servo variable structure, if the oil pressure in the housing exceeds 0.15 MPa, it will affect the sensitivity of the servo mechanism. Pay special attention to it when using it.
2. Connect the two oil drain ports to the oil pipes, the lower oil pipes are supplied with cooling oil, and the higher oil pipes return to the oil tank. Vent holes should be installed at the highest point of the pipeline in the closed oil circuit to remove the air in the oil and avoid vibration and noise.
In order to prolong the service life of the hydraulic oil pump, oil samples must be taken out regularly for inspection at the turbulent flow of the oil circuit. Maintaining the cleanliness of the oil is an important part of system maintenance. Sometimes the system cannot operate normally because the control valve spool is stuck by the oil, or it is damped and does not move smoothly. If there is no other reason for failure, cleaning the related control valve (especially the proportional valve) is an important measure. The damage of the axial plunger pump starts from the wear of the plunger shoe, as shown in the figure below. When the sliding shoe wears to the point where it cannot form a hydrostatic oil film with the swash plate, the friction between the shoe and the swash plate will increase, the swash plate will be strained, the friction will increase further, the return plate will rupture, and the interior of the pump will be damaged. Therefore, the wear and tear (not completely damaged) shoes can be replaced regularly to avoid damage to the entire pump.
During use, pay attention to check the following:
1. Regularly check the moisture, mechanical impurities, viscosity, acid value, etc. of the working hydraulic cylinder oil. If it exceeds the specified value, purification measures should be taken or new oil should be replaced, and it is absolutely prohibited to use waste oil without purification treatment, and fake and inferior oil that does not meet the specified standards after purification.
2. Always check the case temperature of the hydraulic pump. The maximum temperature at which the shell is fully exposed should generally not exceed 80°C.
3. Do not disassemble the hydraulic pump easily during regular maintenance of the main hydraulic cylinder. When it is determined that there is a fault and need to be disassembled, be sure to pay attention to the cleanliness of the disassembly and assembly tools and the disassembly and assembly environment, and the parts that are disassembled must be protected from scratches and fuzzes; when assembling, all parts must be cleaned, oiled and lubricated, and attention should be paid to the installation position. Don’t make a mistake.
4. Replace the clogged filter element in time. The new filter element must confirm its filtration accuracy, and it cannot be used if it fails to meet the requirements.
5. When the hydraulic pump is not used for a long time, the original oil in the shell should be discharged, and then filled with oil with lower acid value. The exposed processing surface should be coated with anti-rust oil, and each oil port should be sealed with screw plugs. Prevent dirt from entering.