Created on:2021-12-03 13:31

Fault analysis and elimination of noise produced by external meshing gear pump

Fault analysis and elimination of noise produced by external meshing gear pump

The main causes of the noise of external gear pump are: the noise of flow pulsation, the noise of trapped oil, the noise of poor tooth profile accuracy, the noise of air entry, the noise of uneven bearing rotation, etc. The causes of various frequent noises are analyzed as follows.

1) Noise caused by air leakage at weak sealing links.

① The gland and the pump cover are not well matched and air intake occurs. There are three glands (non protruding end of driving shaft and two ends of driven shaft) on the front and rear pump covers of CB-B gear pump. These three glands are assembled with the corresponding mounting holes on the pump cover according to a certain matching relationship. At present, the gland used is made of cast iron bar, powder metallurgy parts and plastic parts. When the appropriate interference between the outer circle of the gland and the pump cover hole cannot be guaranteed due to processing errors, or the plastic gland is damaged, the air will be introduced from places 1, 2 and 3 in figure 3 and 7. At this time, knock out the gland and replace it with qualified parts. The leakage at the pump cover and plastic gland can be sealed with epoxy resin and other adhesives.

② Intake air from the pump rear cover oil inlet (tapered pipe thread) connection. If the taper pipe threaded joint is loose due to poor fit, or the sealing at the pipe joint is poor, it is possible to intake air from the middle. At this time, it can be solved by winding a layer of tetrafluoroethylene bag on the pipe joint, sealing, tightening the pipe joint or replacing the qualified pipe joint.

③ Intake air from L in the joint surface between the pump body and the front and rear covers (Fig. 38). The plane seal pressed by screws between the pump body and the front and rear covers is hard contact. If the contact plane is not well machined and its flatness and surface roughness are not good, it is easy to intake air from 1 in Figure 3-8. The pump can be disassembled to grind the pump body and the pump cover. When the flatness of the pump body or pump cover cannot meet the specified requirements, it can be ground back and forth with steel sand on the flat plate according to the "8" line, or on the surface grinder to make its flatness not exceed YM, and it is necessary to ensure the perpendicularity between the plane and the hole.

④ Intake air from the pump shaft oil seal. The pump shaft is sealed with skeleton oil seal. When the spring clamping the lip falls off or the oil seal is reversed during assembly, and the lip is pulled or aged and damaged due to use, because the rear end of the oil seal is often in a negative pressure state, the air will enter the pump from 2 places in Figure 3 and 8. Generally, it can be solved by replacing a new oil seal.

⑤ The installation position of the hydraulic pump is too high from the liquid level. When the hydraulic pump works, it needs a large vacuum to ensure its normal operation. At this time, if the working conditions do not change accordingly, it will cause insufficient oil suction and air intake of the hydraulic pump, especially when the pump speed decreases. However, when the pump sucks oil, the vacuum should not be too large. When the pressure in the pump sucking chamber is lower than the gas separation pressure of the oil at this temperature, the air will precipitate. When the pressure in the pump sucking chamber is lower than the saturated vapor pressure of the oil, cavitation will be formed, resulting in noise and vibration.

⑥ The oil return pipe orifice that should not be exposed to the liquid level exposes the oil level, and sometimes the air will be backfilled into the system due to the instantaneous negative pressure in the system. Therefore, some oil return pipes should be inserted below the liquid level when necessary.

⑦ Too little hydraulic oil in the oil tank reduces the liquid level, resulting in the exposure of the oil filter on the liquid level. When the hydraulic pump is working, the pump sucks air. In this case, the hydraulic oil shall be added to the oil mark in time.

⑧ The hydraulic oil throughput of the oil suction filter is too small. When the oil suction filter is blocked by dirt due to long-term use and not cleaned in time, or the capacity of the oil filter is too small, resulting in increased oil suction resistance and air intake. In addition, most of the oil inlet and outlet diameters are too large, it is possible to bring in air. At this time, the oil filter can be cleaned and the oil filter with large capacity can be selected, And properly reduce the diameter of oil inlet and outlet to eliminate it.

2) Noise caused by mechanical reasons and its elimination.

① The gear is seriously worn and produces noise. As the hydraulic pump has been used for a long time, especially due to the increased gear wear or the occurrence of strain and galling caused by the pollution of hydraulic oil, when this phenomenon occurs, the filtration of hydraulic oil shall be strengthened or the hydraulic oil shall be replaced in time. At the same time, the gear pump shall be disassembled for cleaning. If the gear is seriously worn, it shall be studied or "replaced".

② Noise is generated due to problems in the installation and connection quality of the coupling. The installation of the hydraulic pump shaft and the motor shaft is required to ensure concentricity. Generally, flexible connection shall be adopted. If the coupling connected between the pump shaft and the motor is not concentrically installed, there will be noise caused by collision. At this time, check whether the roller and rubber ring of the coupling are damaged. If damaged, replace them in time to ensure safety Verify the concentricity of pump shaft and motor shaft, as shown in Figure I.

③ Noise caused by poor machining accuracy of gears. The machining accuracy of gears is poor, and large noise will be generated during gear meshing, which is mainly caused by large errors in four aspects: tooth profile error, tooth direction error, ring gear radial runout and tooth surface finish. At this time, as a manufacturer of gear pump, qualified gears can be replaced. As a user unit, the gear can be grinded. At present, most hydraulic parts factories use modified gear as gear pump, which can reduce noise.

④ Because the inner hole of the gear is not perpendicular to the end face or the axis lines of the two shaft bearing holes on the front and rear covers are not parallel, after the assembly, the two gear shafts (upper and short shafts) intersect obliquely, resulting in inflexible gear rotation and uneven weight, and periodic vibration and noise will be generated during the operation of the gear pump. The manufacturer of hydraulic parts shall ensure the perpendicularity of gear, long and short shafts, front and rear cover bearing holes and the parallelism of shaft holes from the process. Unqualified ones are not allowed to enter the final assembly.

⑤ Noise caused by damaged transmission parts of gear pump. Due to the long-term use of the gear pump, wear can not be avoided, and the transmission parts of the gear pump will be damaged over time. For example, the needle cage of the bearing is damaged, and the long and short shaft journal and needle are worn, resulting in poor rotation accuracy of the bearing and radial unbalanced pressure, resulting in mechanical noise. At this time, it is necessary to disassemble and repair the gear pump and replace the needle roller bearing.

3) Noise caused by oil trap.

Gear pumps, vane pumps and plunger pumps used in hydraulic transmission are positive displacement pumps. In hydraulic transmission, the hydraulic pump works by increasing and decreasing the volume of two or more sealing cavities. The oil suction cavity and oil pressure cavity must be separated by a certain distance and interval. The oil trapping phenomenon of gear pump has been mentioned earlier. Please refer to the previous content and will not be repeated here.

4) Noise from other causes.

① Noise caused by excessive viscosity of hydraulic oil. At this time, the hydraulic oil with appropriate viscosity shall be selected.

② Noise caused by too high speed of hydraulic pump or too high altitude of hydraulic pump. When the rotating speed of the hydraulic pump is too high or the working altitude is too high, the vacuum at the oil inlet of the hydraulic pump will increase and there will be noise. At this time, adjust the rotating speed within the normal range or select appropriate working conditions.

③ Noise caused by too small diameter of oil inlet pipe of hydraulic pump. When the diameter of the oil inlet pipe is too small, the oil inlet resistance will increase, the vacuum degree of the hydraulic pump will increase and the noise will appear. At this time, the oil suction pipe with larger diameter shall be selected.

④ The noise generated by the parallel relief valve at the outlet of the hydraulic pump is mistaken for the noise of the hydraulic pump. In case of this problem, refer to the overflow valve fault diagnosis for treatment.

Home    Article    Fault analysis and elimination of noise produced by external meshing gear pump