For the sliding bearing with external forced oil supply, if the labyrinth oil baffle often leaks oil, try adding an oil throwing pan.
Abstract: Through a specific example, this paper describes in detail the source of oil retaining leakage in the pump bearing chamber. On how to solve the problem of recovery, the structure of helmet bearing chamber is improved.
Key words: booster pump, sliding bearing, oil baffle, oil leakage, structural improvement
Oil leakage from the pump bearing chamber of the power plant is one of the major problems affecting the environmental protection of the plant and the operation stability of the equipment, which is very concerned by the pump maintenance personnel.
Ynkn40g / 300 booster pump is used for the boiler feed pump of phase II unit of Jinzhou Donggang Power Co., Ltd The oil baffle of the pump bearing chamber has leaked oil for many times In the process of dealing with oil leakage, we made some analysis and put forward structural improvement measures,
1. Structural features of bearing
The support bearings at both ends of the pump adopt split sliding bearings (Fig. 1), and its structural characteristics are as follows:
1.1 Oil supply mode
The lubrication mode of external forced oil supply is adopted, that is, the lubricating oil is directly injected into the oil inlet of the bearing through the pressure oil pipeline, and the oil quantity is controlled by the throttle orifice installed on the oil pipeline to forcibly lubricate the bearing.
1.2 Sealing mode
In order to prevent the lubricating oil from leaking, labyrinth rings are installed on both sides of the auxiliary bearing body. The small gap between the shaft and the labyrinth ring is sealed, and an oil return hole is opened between the labyrinth teeth. A very small amount of oil leakage returns to the bearing chamber through the oil hole.
2. General causes of oil leakage in bearing chamber and measures taken
From the bearing structure of the pump and many times of maintenance and repair, we summarized the general causes of oil leakage in the bearing chamber.
2.1 High lubricating oil pressure
The sliding bearing (forced oil supply) of any rotating equipment has certain requirements for the oil supply pressure. If the oil pressure is too high, it is easy to increase the amount of oil coming, and the oil return is not smooth, resulting in oil leakage from the oil baffle of the bearing chamber. The oil pressure of each bearing of the pump is designed to be (0.07 ~ 0.15Mpa). If the oil pressure is higher than the upper limit, the hole diameter of the lubricating oil pressure control valve or throttle orifice can be adjusted.
2.2 The orifice diameter is too large or the orifice is omitted during maintenance
The hole diameter of the orifice plate in the pipeline has been adjusted according to the oil required by the bearing during the installation and commissioning of the pump. Generally, the hole diameter is (1 ~ 2) mm. Do not easily change the hole diameter during the maintenance process, resulting in an obvious increase in the amount of oil coming and the oil cannot be discharged in time. In addition, the throttle orifice must not be omitted when reinstalling the oil pipeline after the maintenance, which often occurs in the maintenance process.
2.3 Excessive clearance caused by long-term wear of labyrinth ring
Excessive radial clearance of labyrinth ring is the main cause of oil leakage in bearing chamber. Generally, the unilateral clearance between labyrinth ring and shaft is 1.5/1000 ~ 2 / 1000 of shaft diameter. If the clearance exceeds the standard, the labyrinth ring must be repaired or replaced.
2.4 The oil return hole on the labyrinth ring is blocked
The blockage of the oil return hole is also one of the main causes of oil leakage in the bearing chamber. Due to the blockage of the oil return hole, a small amount of oil leakage cannot return to the bearing chamber in time through the oil return hole and leak out. Therefore, it is necessary to clean the lubricating oil and the bearing room.
2.5 The oil return pipeline is blocked or blocked
It is also common for the oil return pipeline to be blocked by foreign matters. The bearing chamber is full of oil due to the blocked oil return, which leads to oil leakage in the bearing chamber. Therefore, in the reassembly stage of the maintenance process, the oil pipeline must be cleaned to prevent sundries from being left in it.
2.6 Poor smoke exhaust of oil return tank
As the oil return temperature of the oil system is relatively high, a certain amount of oil fume will inevitably accumulate in the oil tank. If the smoke exhaust is not smooth, it is very easy to form micro positive pressure in the oil tank, resulting in poor oil return and oil leakage in the bearing chamber.
3. Special causes and measures of oil leakage in bearing chamber
3.1 Further cause analysis
The gap between the bearing shells is too large or the scraping and grinding process of the calcium surface of the bearing shells is poor, resulting in groove marks and deflection, resulting in poor contact between the shaft and the bearing shells. When the pressure oil flows out from both sides of the bearing shells, it does not overflow slowly, but in a spray shape. The distance between the two ends of the bearing shells and the labyrinth ring is very close, and the sprayed pressure oil splashes directly on the labyrinth teeth. In this way, the clearance seal of the labyrinth ring alone cannot seal such a large amount of pressure oil. In addition, the oil return hole is small, so the oil cannot be returned in time, resulting in oil leakage in the oil baffle of the bearing chamber.
After an overhaul of the unit, oil leakage occurred in the bearing chamber of the pump. When dealing with this defect, we still have oil leakage after using the above methods as usual. Finally, careful research and analysis are carried out, and it is considered that it is caused by the poor contact between the pump shaft and the bearing bush.
3.2 Improvement measures
In view of the above special causes of oil leakage in the bearing chamber, we refer to the oil baffle sealing mode of the bearing chamber of rotating equipment such as r16k-550 coupling and dg750-180 feed pump: the oil slinger or the combination of labyrinth teeth and oil slinger is adopted, and it is decided to install a simple oil slinger between the bearing bush and labyrinth ring on the shaft (Fig. 2)
The oil slinger is generally fixed to the shaft by tightening force or set screw. Some oil slingers are also added with sealing rubber rings between the oil slinger and the shaft diameter, so there is no gap between it and the shaft in theory. In this way, even if there is pressure oil ejected from both sides of the shaft after installing the simple oil spilling pan, it will be directly ejected onto the oil spilling pan, which will be blocked back to the bearing chamber and will not be directly sprayed onto the labyrinth teeth. For a small amount of oil splash, the labyrinth teeth can completely block and recover through the oil return hole. Practice has proved that our analysis and measures are correct. After installing a simple oil slinger, the bearing chamber of the pump will no longer leak oil.
For the sliding bearing with external forced oil supply, if the labyrinth oil baffle often leaks oil, it may be analyzed and solved according to the above general reasons. If the traditional maintenance methods are ineffective, it may be better to try adding an oil throwing pan.
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