Fault analysis of low oil pressure of the hottest

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Cause analysis of low oil pressure of excavator

when an excavator is working, an oil fault alarm suddenly appears on the instrument panel. The driver immediately stops to check, and checks the oil level and viscosity through the oil dipstick. Is it normal that its constituent components are undefined? Remove the oil filter element and check whether the filter element is normal? The inspection results of the above two items are normal, because there is no suitable detection tool, so it is impossible to carry out further inspection. The customer hopes that we can help them carry out further inspection to eliminate the fault and restore the machine to normal use. What causes the abnormal oil pressure during engine operation? We first make a detailed cause analysis

the lubrication system of diesel engine is mainly composed of oil pan, oil pump, oil filter, radiator, main oil duct, oil distribution duct, low oil pressure alarm sensor, high oil temperature alarm sensor, pressure limiting valve and bypass valve. The main reasons for low oil pressure are as follows:

1. Insufficient oil volume

if the oil volume is insufficient, the pump oil volume of the oil pump will be reduced or the pump will not be oiled due to entering air. The stop and rotary table should be free of damage and cracks to reduce the oil pressure, and the crankshaft and bearing, cylinder liner and piston will be aggravated by poor lubrication. Therefore, check the oil level in the oil pan before working every day to ensure that the oil level is normal. If it is insufficient, add the same type of oil produced by the same manufacturer

2. The oil pump does not rotate

if the drive gear of the oil pump and the flat key of the drive shaft are damaged or fall off; The damage of the filter collector will make the oil pump suck in foreign matters, and the gear is stuck, which will stop the oil pump and reduce the oil pressure to zero. At this time, replace the damaged flat key or filter collector

3. Oil pump wear

when the clearance between the oil pump shaft and the bushing, the clearance between the gear end face and the pump cover, the tooth side clearance or the radial clearance is too large due to wear, it will lead to the reduction of pump oil volume and the decrease of oil pressure after years of development. At this time, the worn parts should be replaced, and the inner plane of the pump cover should be ground to restore the gap between it and the gear end face to the standard range

4. If the engine temperature is too high, carry out statistical analysis of group patterns

if the engine cooling system has too much scale, poor heat dissipation, long-term overload operation or the fuel supply time of the fuel injection pump is too late, the engine will overheat, accelerate the aging, deterioration and thinning of the oil, leak from each fitting gap, and reduce the pressure. The scale should be removed, the oil supply time should be adjusted, and the engine should work within the rated load

5. The fitting clearance between the main bearing and the connecting rod bearing increases

after long-term use of the engine, the fitting clearance between the main crankshaft and the connecting rod bearing gradually increases, the leakage increases, and the oil pressure decreases. The pressure will decrease by 0.01Mpa when the fitting clearance increases by 0.01mm. At this time, the crankshaft can be repaired, new connecting rod bearings and main bearings can be selected, and their matching clearance can be restored

6. The bypass valve is damaged

in order to maintain the normal oil pressure of the main oil passage, a bypass valve is set. If its pressure regulating spring is softened or improperly adjusted, and the mating surface between the valve seat and the steel ball is worn or stuck, and it is not tightly closed, the return oil volume increases, and the pressure of the main oil passage will decrease. At this time, remove the bypass valve for inspection, and finally adjust the pressure to the normal range

7. Oil leakage from the oil radiator

external leakage will pollute the engine surface and reduce the pressure; Internal leakage makes the oil enter the water tank, the heat dissipation effect of the cooling system becomes worse, the engine overheats, the oil becomes thinner, and the pressure drops. Remove the radiator, repair or replace it, and restore its function

8. The pressure sensor fails or the oil passage is blocked

if the pressure sensor fails or the oil passage from the main oil passage to the pressure sensor is blocked and the oil flow is blocked, the oil pressure will drop. Do the following inspections: idle the engine, loosen the oil pipe connector, observe the oil flow, judge the fault position, replace the pressure sensor or clean the oil passage

9. The set pressure of the pressure limiting valve is too low

in the lubrication system, the oil pumped by the oil pump must ensure appropriate pressure before reaching all lubricating parts of the engine. If the set pressure of the pressure limiting valve is too low, the pressure regulating spring becomes soft or the sealing surface leaks, the set pressure will be too low. At this time, adjust the pressure limiting valve to make the pressure return to normal

10. The oil grade is not appropriate

different engines need to add different grades of oil, and the engine of the same model should also choose different grades of oil in different seasons. If the selected engine oil is not suitable or of poor quality, the leakage will increase and the pressure will decrease due to the low viscosity when the engine is running. The engine oil should be selected correctly and reasonably to adapt to different models or seasons

11. The oil filter is blocked

when the oil filter is blocked and cannot flow, the bypass valve on its base is opened, and the oil directly enters the main oil passage without filtering. If the opening pressure of the bypass valve is set too high, when the oil filter is blocked, it cannot be opened in time, the oil pump pressure will rise, the internal leakage will increase, the oil supply to the main oil passage will decrease, and the oil pressure will decrease. Ensure that the oil filter is clean; Correctly adjust the opening pressure of the bypass valve, timely replace or repair the damaged components or mating surfaces, and restore its normal working performance

12. The filter collector is blocked

under normal circumstances, the oil pressure at high throttle should be higher than that at low throttle, but sometimes abnormal conditions will occur. If the oil is too dirty and sticky, it is easy to block the filter collector. When the engine runs at a low speed with a small throttle, the oil pressure is normal because the oil pump does not absorb much oil, and a certain pressure can be established in the main oil passage; However, when the throttle is increased and the engine operates at a high speed, the oil absorption of the oil pump will be significantly reduced due to excessive resistance of the filter collector, so the indication of the oil pressure gauge will decrease due to insufficient oil supply in the main oil passage. Clean the suction filter or change the oil

through the above analysis, we took the oil pressure gauge and oil quality analyzer to the construction site, and tested the quality of the oil with the oil quality analyzer. It was found that the viscosity and pollution degree of the oil met the requirements. Connect the oil pressure gauge and measure the oil pressure at low speed and high speed respectively. It is found that the oil pressure is lower than 0.15Mpa. Under normal circumstances, the oil pressure is 0.15Mpa at low speed and 0.6MPa at high speed. In this way, we can know that the oil pressure is low and cannot reach the normal pressure. We checked the bypass valve on the oil filter base according to the principle from simple to complex, from the outside to the inside. After disassembly, we found that the seal between the steel ball and the valve seat mating surface was not tight, resulting in oil leakage and pressure reduction. By grinding the sealing surface, restore its sealing performance, adjust the pressure to reach the standard value, and the oil pressure alarm light goes out, indicating that the machine returns to normal and the fault is removed

by eliminating this fault, it shows that mechanical failure is not terrible. As long as you understand the working principle of the system and analyze it carefully, you can eliminate the fault, but don't disassemble it blindly, otherwise, you will get twice the result with half the effort, and even damage the components that work normally

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