Hydraulic pump selection
When choosing a hydraulic pump for the hydraulic system of the host, it should first meet the requirements of the host for its hydraulic system, flow, working pressure, etc., and then comprehensively consider the performance, use and maintenance of the pump according to the characteristics of the host.
When selecting the type of pump, the pump should have a certain pressure reserve, and the rated pressure of the general pump should be slightly higher than the system pressure.
If the hydraulic system uses a single pump system (a pump supplies oil to several working circuits simultaneously or at intervals), the pump pressure should be selected according to the working pressure required by the highest working circuit.
In the hydraulic system, the hydraulic pump is usually driven by an engine or a motor, and when selecting the speed of the pump, it is required to work at its rated speed, so as to give full play to its work efficiency. At the same time, the pump speed cannot exceed the maximum speed specified by the pump. The high speed of the pump will make the pump insufficient oil, reduce the life, and even damage the pump in advance. In addition, because the amount of oil supplied by the pump depends on the displacement and speed of the pump, so in a single pump system, when selecting the pump, if the working loops are not working at the same time, the working loop with the largest required flow is selected to select the hydraulic pump, if there are several working loops working at the same time (including or excluding the loop with the largest required flow), the required flow exceeds the required flow of the largest loop. The hydraulic pump should be selected according to this flow rate.
Hydraulic motor selection
The selection of low speed hydraulic motor is introduced here, and the performance of high speed hydraulic motor is similar to the nature of similar pumps, which is no longer told.
The use of pressure is one of the main parameters of the hydraulic motor, multi-action motor (internal curve motor) and single action motor (crankshaft connecting rod motor), due to the plunger more, the cylinder body force balance, so the use of high pressure, rated pressure up to 25MPa~30MPa, while the crankshaft connecting rod motor is between 16MPa~21MPa. In addition to the efficiency limitation, the further increase of pressure shows that the life of roller bearing is shortened for the internal curve motor, and the specific pressure of the tangential force transfer mechanism of the beam and the contact stress of the guide rail are larger. For crankshaft connecting rod motor, the life of bearing and friction pair is shortened.
The speed of the hydraulic motor depends on the inlet flow, displacement and volumetric efficiency. However, for a certain type of hydraulic motor, there is a maximum working speed due to the influence of inertial force and the flow rate limit of the internal channel. The maximum speed of the internal curve motor is lower than that of the crankshaft connecting rod motor, generally not more than 150r/min, while the speed of the crankshaft connecting rod motor can reach 300r/min.
The minimum stable speed is also the main parameter of the low-speed motor, the minimum stable speed of the hydraulic motor, the crankshaft connecting rod type is about 10/min, and the quality can reach 2r/min. The internal curve motor can reach 0.2r/min~0.5r/min. This is mainly because the flow pulsation of the latter can theoretically be equal to zero.
The efficiency of the hydraulic motor varies greatly with the design and manufacturing quality and the use conditions. Because the leakage line of the inner curve motor is long and the sealing length is short, it is most easy to leak. The test data show that the internal leakage is 8 to 10 times of the external leakage, or even larger. Therefore, the volumetric efficiency is lower than that of the crankshaft connecting rod type. Good quality can reach 90% to 93%, and the crankshaft connecting rod motor can reach 95%.
