The normal oil working pressure of diesel engine should be between 0.25mpa and 0.35mpa, in which the new engine or the machine temperature can be higher when low, and the old engine or the machine temperature is high when low. When the machine is in operation, if the oil pressure is lower than 0.2mpa or goes up and down with the change of rotating speed, or even drops to zero suddenly, it indicates that there is a problem inside the machine, the engine should be shut off immediately to find out the reason, and restart after troubleshooting. Otherwise, it will lead to the burning of the valla cylinder of the big accident. Here are some examples we encountered:

1. Insufficient oil output from the oil pump causes oil pressure drop

Oil pump gear pump and two kinds of rotor pump. Some gear pumps (such as 4125 diesel engine on the pump pump), the pump cover and pump body joint surface roughness is very low, the original design without gasket, if the maintenance of another paper pad, it will increase the gear end face clearance, but will reduce the output of oil pump. However, there is a gasket at the joint surface between the pump and the cylinder block. If the gasket is missing, the pressure oil from the oil pump will leak outwardly, thus causing the oil pressure to drop. Some rotor pump, its outer rotor side chamfering Angle, the other side without chamfering Angle, if installed in reverse, oil output can be reduced by 40% - 60%. In addition, the gear or rotor radial and end face clearance due to wear and tear when too large, will lead to the reduction of oil output pump and oil pressure drop of the adverse consequences. The repaired oil pump should adjust the opening pressure of the pressure limiting valve on the test bench to keep it between 0.5-0.7mpa. If the pressure is too high, it will accelerate the wear of the oil pump; If the pressure is too low, it will lead to the main oil channel pressure drop. Pump installation should be filled with oil, so as not to pump air and can not absorb oil. The connection between the oil pump and the oil suction pan must be sealed. If air leakage, it will reduce the oil output of the pump.

2. Oil pressure drops due to clogged oil filter

When the oil filter is blocked and the oil cannot pass through smoothly, the safety valve on the base of the filter will be pushed open, so that the oil can enter the main oil channel without filtering. However, if the safety valve opening pressure is too high and cannot be opened in time, it will increase the leakage of the oil pump and reduce the oil supply to the main oil channel, and the oil pressure will decrease accordingly. The oil filter shall be maintained on time, and the safety valve opening pressure shall be adjusted to 0.35-0.45mpa. In addition, if the safety valve spring aging, the valve seat and the steel ball seal is not strict, the oil will be a large number of leakage, and cause oil sump oil bubble, at this time to draw out the oil ruler can see full of foam oil.

3. Damage of oil return valve causes oil pressure drop

In order to maintain the normal oil pressure of the main oil channel, the oil return valve is set here. If return oil valve spring softens or adjusts undeservedly, the valve seat and the steel ball match the surface to wear away or is stuck by the dirty matter to close loosely, its return oil quantity to rise greatly, the main oil path engine oil pressure also then drops. The oil return valve should be overhauled to adjust the opening pressure between 0.28 and 0.32MPa. In addition, if the return oil valve opening pressure is too low, the machine will cause the return oil valve to open and close frequently, resulting in the oil pressure gauge pointer swing back and forth, the main oil channel is also prone to occur because of insufficient oil supply shingle accident.

4. Oil pressure drop due to oil leakage from oil radiator

Oil leakage not only makes the machine dirty, but also leads to the oil pressure drop, should be removed from the radiator welding repair, after the pressure test qualified before installation. Some machines such as the United States E200 excavator and domestic t-120 bulldozer, the oil radiator directly placed in the cooling system of the body, if the radiator oil leakage, machine operation because the oil pressure is higher than the cooling water pressure, the oil in the radiator will flow into the water; When the machine off, cooling water will infiltrate the radiator, so that the oil quickly emulsified deterioration. Should take out radiator to weld repair, and replace the failure of the oil, can work again.

Additional, oil radiator and pipeline if be blocked by dirt, also can increase because of resistance and make oil flow decreases, pressure drops. Should dredge in time, restore its normal current capacity.

5. Excessive clearance between crankshaft and bearing bush causes oil pressure drop

After long-term use of the machine, crankshaft and connecting rod shoe or crankshaft with the main shaft shoe with the gap gradually increased, thus forming an oil wedge, oil pressure has been falling. According to the measurement, the oil pressure decreases by 0.01MPa for every 0.01mm increase in the clearance. Therefore, this is not only one of the main reasons of too low oil pressure, but also can be used to judge the degree of wear of crankshaft and bearing bush and whether the diesel engine should be overhauled. The crankshaft should be polished and the bearing bush of the corresponding size should be selected to restore the fitting clearance to the normal technical standard.

6. The oil pressure fluctuates between high and low due to the blockage of the oil suction pan

In general, the oil pressure is higher at the higher throttle than at the lower throttle, but sometimes there are anomalies. If the oil is too dirty and too viscous, it is easy to block the oil suction pan. Therefore, when the diesel engine operates at low speed with small throttle, the oil suction of the oil pump is not large, and the main oil channel can still establish a certain pressure, so the oil pressure is normal. However, when the throttle is increased at high speed, the oil absorption capacity of the oil pump will be significantly reduced due to the large resistance of the oil suction disc, so the oil supply from the main oil channel is insufficient, and the oil pressure will decline. Clean the oil suction pan and replace it with a new oil. In addition, when the main oil way back oil valve spring is broken or bending partial grinding and hole wall occurs stuck, the valve open and close not only to overcome the resistance of the spring, but also to overcome the stuck force, so open and close is not sensitive. If the diesel engine throttle operation, the valve in the closed state, the main oil channel can maintain a certain pressure; However, due to the sharp increase of oil supply, the oil return valve suddenly opens and the oil pressure drops, and the oil return valve fails to return to its position in time due to the stuck spring. Therefore, it is more difficult for the main oil channel to maintain the proper pressure than the small throttle, which is one of the reasons why the oil pressure is lower than the small throttle when the large throttle operates.