Oil pressure is the pressure value reflected on the oil pressure gauge of the main oil passage of a diesel engine. Whether this value is normal or not is an important indicator of the normal operation of the diesel engine lubrication system. Low oil pressure indicates poor lubrication of the friction surfaces of various components, which can lead to early wear of the components or serious accidents such as burning tiles and holding shafts over time. If the reading on the oil pressure gauge is below the lower limit of the standard or there is no pressure indication, the cause should be immediately eliminated.
1. Main reasons
The oil pressure gauge is malfunctioning or the oil circuit leading to the pressure gauge is blocked. Diesel engine oil sump oil is insufficient. The oil pump is severely worn or the suction filter is clogged. The pressure regulating valve and return valve are not tightly closed, or the spring becomes soft, bent, or broken, or the pressure adjustment is too low. The opening pressure of the oil pump pressure limiting valve is low. The steel ball and valve seat of the return valve are worn, the sealing is not tight enough, and there is oil leakage. The paper gasket of the oil pump is damaged and there is oil leakage. Lubricating parts such as the main bearings, connecting rod bearings, camshafts, and shaft sleeves of diesel engines are worn, resulting in increased clearances and excessive leakage of lubricating oil. The oil grade is incorrect and the viscosity is low. The oil coarse filter is clogged, and at this time, the opening pressure of the safety valve is high, causing the pressure of the oil in front of the filter to increase, forcing the internal leakage of the oil pump to increase, reducing the amount of oil in the main oil passage, resulting in a decrease in pressure. Insufficient oil supply from the oil pump. The centrifugal rotor fine filter has serious oil leakage.
2. Fault diagnosis
(1) Use a dipstick to check the oil level in the oil pan. The dipstick is engraved with upper and lower limit marks, and the lowest oil level must not be lower than the lower limit mark. When measuring with a dipstick, it is important to ensure that the dipstick is straight and not bent, otherwise the measurement will be inaccurate; Accurate measurements must be taken 30 minutes after the diesel engine has been turned off.
(2) Check the viscosity of the engine oil. Insufficient viscosity of engine oil can cause poor lubrication of machine parts and a decrease in oil pressure. The reasons for insufficient oil viscosity are multifaceted, such as incorrect oil grades; Diesel or water leaks into the engine oil; The clearance between the cylinder piston and piston ring is too large, causing exhaust gas to be discharged into the oil pan and causing the oil to become thinner due to heating; The poor heat dissipation performance of the oil radiator can cause the oil temperature to become too high and thin. Targeted exclusion should be carried out based on different reasons. The viscosity of engine oil can be tested by comparison method. Use two glass test tubes of equal diameter and length, one containing an oil with a known standard viscosity, and the other containing the oil to be measured. Place the two test tubes at the same height and do not fill the tubes with oil, leaving a gap. Then use a wooden stopper to seal the bottle mouth, invert the two test tubes 180 ° and shake them a few times, and observe the occurrence of "bubbles" and "bottle hanging" in the oil inside the bottles. Oil bubbles with low viscosity produce more, have smaller diameters, rise faster, and disappear faster, resulting in less "bottle hanging" of the oil film; Oil with high viscosity produces fewer bubbles, with larger bubble diameters, slower ascent and disappearance, and more oil film "bottle hanging". To identify the water content in the engine oil, put the oil sample into a glass tube and heat it on an alcohol lamp. When the temperature is close to 80~100 ℃, listen carefully and observe. If there is a "clatter" sound and foam, and the oil becomes turbid, it means that there is water in the oil.
(3) Check if the oil pressure gauge is malfunctioning. Stabilize the diesel engine to operate at low speeds (500-600 revolutions per minute). Use a wrench to loosen the nut at the connection between the machine body and the oil pipe of the oil pressure gauge. If oil flows outward and there is a certain pressure, it indicates that there is a certain oil pressure in the main oil passage. At this point, remove the oil pipe, blow it through with a nozzle or air hose, and then install it to test the pressure again. If the pressure gauge reading is still low, it is a failure of the oil pressure gauge. If it is an inductive oil pressure gauge, when checking, first remove the wire of the pressure sensing plug and ground it directly to the machine body. If the pressure gauge reading rises rapidly, it indicates that the oil pressure gauge is good and the fault lies in the pressure sensing plug. The pressure sensing plug can be removed, and the oil hole exposed by removing the pressure sensing plug can be covered with a rag or fingers. Starting the diesel engine, if there is sufficient oil sprayed from the hole without bubbles, it indicates that the pressure sensing plug is damaged and ineffective; If the reading on the oil pressure gauge is low and the oil pressure from the installation hole of the pressure sensing plug is insufficient, it indicates that the cause of the fault is insufficient pump oil pressure of the oil pump, not a malfunction of the oil pressure gauge.
(4) Check if the oil filter is clogged. The filter is severely clogged, which will cause a decrease in oil pressure in the main oil circuit. It is necessary to clean or replace the filter element in a timely manner.
(5) Debug the pressure regulating valve. Under normal circumstances, when the adjustment screw of the pressure regulating valve is screwed in, the pressure value of the oil pressure gauge should increase accordingly. If the adjustment is ineffective, it may be due to valve wear or dirty padding causing oil leakage, or it may be due to the pressure regulating valve spring becoming soft or broken. It should be disassembled and inspected.
(6) Check whether the centrifugal rotor type fine filter leaks oil. The common cause of oil leakage is that the clearance between the shaft sleeve and the nozzle of the rotor are worn out. At this point, the oil flowing out of the fine filter accounts for 25% to 30% of the total flow rate, which reduces the amount of oil flowing into the coarse filter and main oil passage, resulting in a corresponding decrease in the locomotive's oil pressure value.
(7) Check if the suction disc filter in the diagnostic oil pan is clogged. After the oil suction plate filter is blocked, the oil pressure gauge indicates a low and unstable oil pressure value. When disassembling the oil pipe joint of the oil pressure gauge, bubbles will be found to emerge.
(8) Check if the oil pump is severely worn. When the oil pump is severely worn, it should be sent to a repair shop for inspection and testing. If checking in the car, non dismantling inspection instruments can be used.
(9) Check the opening pressure value of the pressure limiting valve. When the opening pressure value of the pressure limiting valve is low, the oil pressure value is often high when the locomotive is cold, and when the locomotive temperature rises, the oil pressure value quickly decreases. At this point, adjusting the pressure regulating valve does not work or has little effect.
(10) Diagnose whether the clearance between the bearing shells is too large. When the clearance between the bearing shells is too large, in addition to the phenomenon of low oil pressure, there may also be noise caused by loose fit between the shaft and the bearing shell. The larger the clearance between the bearing shells, the louder the knocking sound, and the more oil leaks from the clearance during operation, the lower the oil pressure in the main oil passage. According to experiments, after an average bearing wear of 0.01 millimeters, the main oil passage pressure will decrease by 0.1 kilopascals But this method is only more accurate when the bearings are generally worn evenly. When individual bearings are severely worn, it is impossible to accurately indicate the technical status of the bearings. Therefore, it can only be used as a verification method and cannot be used alone.