Parameter selection and type selection of gear pump
(2) Parameter selection and type selection
① The selection of rated pressure should be based on the working pressure of different systems to select the appropriate gear pump. The rated pressure of the pump should be 1.1 ~ 1.5 times of the opening pressure of the safety valve of the hydraulic system.
② Before selecting the nominal displacement of the pump, the reference value should be calculated according to the flow QV (L / min) of the system, the rotation speed n1 (R / min) of the hydraulic pump and the volumetric efficiency η V (which can be selected or taken as η v = 0.9) of the pump.
As the gear pump is a constant displacement pump, the final pump flow should be consistent with the flow required by the system as far as possible to avoid excessive power loss.
③ The actual speed of the gear pump should be calculated according to the selected nominal displacement of the gear pump and the flow required by the system. When selecting, it should be as close as possible to the rated speed of the product.
④ The determination of the driving power can calculate the required input power (driving power of prime mover) after the determination of the nominal displacement, rotating speed (the maximum working pressure can be taken if it changes within a certain range) and working pressure of the gear pump.
⑤ In order to match and use the power reasonably, two or more pumps can be used to solve the problem of multiple hydraulic sources. Among the multiple pumps selected, the first pump should be able to bear higher load (pressure × flow) than the second pump; the total load of the multiple pump should not exceed the torque that the pump shaft can bear.
⑥ In the case of indoor and environmental noise requirements, attention should be paid to the selection of products with noise control structure. Generally speaking, the noise of external gear pump is larger than that of internal gear pump.
The reliability, economy, convenience of use and maintenance, and timeliness of supply of gear pump should be considered comprehensively. Priority should be given to products that have passed the appraisal of relevant national departments and industries and have mature technology.
(3) Precautions
① Driving gear pump can use motor or internal combustion engine as prime mover. But the transmission device of the pump can not produce additional axial force and radial force on the driving gear shaft of the gear pump. Floating connection must be adopted between the driving gear shaft extension of gear pump and the output shaft of prime mover (such as elastic coupling and cross groove block floating coupling). The radial runout of the coupling is not more than 0.1 mm. When the spline shaft is directly inserted into the spline hole of the transmission shaft of the prime mover for driving, the radial and key side clearance of the internal spline and spline shaft is not less than 0.15 mm, so as to meet the requirements of floating torque transmission and no additional radial force.
When using V-belt or large gear to drive gear pump directly, gear pump with rolling bearing support in front cover should be selected.
② Suction height the suction height of the pump should be as small as possible. The self-priming capacity of gear pump varies with the displacement, and the general requirement is not less than 16kpa. The manufacturing quality also has an effect on the self-priming ability. Generally, the oil suction height of the pump is not more than 0.5m. In the pipeline system with long oil inlet pipeline, the oil inlet pipe diameter should be increased to avoid too large flow resistance and poor oil suction, which will affect the working performance of the pump.
③ Oil selection and filtration work, oil varieties and brands should be strictly in accordance with the provisions of the pump product sample selection, in order to extend the service life of the pump. Most of the early failure of gear pump is caused by oil pollution, so the working oil should be filtered. Due to the low pollution sensitivity of low-pressure gear pump, the filter with lower filtering accuracy can be selected, while the high-pressure gear pump has higher pollution sensitivity, so the filter with higher filtering accuracy should be set in the system.
④ Before the installation and operation of the pump, the pipeline shall be cleaned thoroughly according to relevant regulations (the welded pipeline must be washed after pickling), the dirt and oxide scale shall be removed, the pump shall be filled with oil, and the driving gear shall be rotated through the shaft extension of the pump to make the oil enter the matching surfaces of the pump.
During installation, the pipe joint or flange connecting screw of oil inlet and outlet shall be tightened, and the seal shall be reliable, so as not to cause air suction or oil leakage, which will affect the performance of the pump.
Check whether the rotation direction of the pump is consistent with that of the drive shaft by inching.
It is recommended to disconnect the air from the pump housing for the first time. Before starting, it is necessary to check whether the safety valve in the system is setting the pressure value.
It should be avoided to start the pump with load and stop the pump with load. Before operation, the pump shall be operated with no load for at least 10 minutes and with load for a short time, and then the working condition of the pump shall be checked. The pump shall be free from leakage, excessive heating and abnormal sound.
If the pump is not used for a long time, it is better to separate it from the prime mover. When it is used again, there should be no load operation for not less than 10 minutes, and the above test run routine inspection should be carried out.
