Causes of sudden decrease of excavator speed and low hydraulic oil pressure

A long time, the machine engine speed solution:

There is an hexagon steel wire between the hydraulic pump and the driving machine. You can loosen it 90 degrees, and then there is a positive and negative wire in the hydraulic pump. You can also loosen it by 90 degrees, but the speed of the machine will definitely be slower. Remember not to loosen only one, which will lead to deviation.

Second, the low oil pressure is mainly due to the following reasons:

1, insufficient oil.

If the amount of engine oil is insufficient, the amount of engine oil pumped by the oil pump will be reduced or the engine oil cannot be pumped out due to air intake, which will reduce the engine oil pressure and aggravate the poor lubrication of crankshaft, bearing, cylinder liner and piston. So check the oil level of the oil pan before work every day to ensure the normal oil level. If it is not enough, it is necessary to add the same type of engine oil produced by the same manufacturer.

2. The oil pump does not rotate.

If the Ping Jian of the driving gear and the driving shaft of the oil pump is damaged or falls off; The damaged filter causes the oil pump to suck in foreign matter, and the gear is stuck, which will stop the oil pump and reduce the oil pressure to zero. At this time, the damaged Ping Jian or filter should be replaced.

3, oil pump wear

When the gap between the pump shaft and the oil pump bushing, the gap between the gear end face and the pump cover, the tooth side gap or the radial gap is too large due to wear, the pump oil quantity will be reduced and the oil pressure will be reduced. At this time, the worn parts should be replaced, and the inner plane of the pump cover should be ground, so that the clearance between it and the end face of the gear can be restored to the standard range.

4, the engine temperature is too high

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 engine oil, leak from each matching gap, and reduce the pressure. Scale should be removed, the oil supply time should be adjusted, and the engine should work within the rated load.

5. The filter is blocked

Under normal circumstances, the oil pressure at large throttle should be higher than that at small throttle, but sometimes there will be abnormal situations. If the oil is too dirty and sticky, it is easy to block the filter element. When the engine is running at a low speed with a small throttle, the oil pressure is normal because the oil absorption of the oil pump is not large and a certain pressure can still be established in the main oil circuit. However, when the throttle is increased to run at high speed, the oil absorption capacity of the oil pump will be obviously reduced due to the excessive resistance of the filter screen, so the indicated value of the oil pressure gauge will decrease due to the insufficient oil supply in the main oil circuit. Clean the suction filter or change the oil.

6. The bypass valve is damaged

In order to maintain the normal oil pressure of the main oil passage, a bypass valve is provided. If the pressure regulating spring becomes soft or improperly adjusted, the mating surface between the valve seat and the steel ball is worn or stuck, the oil return increases and the pressure of the main oil circuit decreases. At this time, the bypass valve should be removed for inspection, and finally the pressure should be adjusted to the normal range.

7. Oil radiator leaks oil

External leakage will pollute the engine surface and reduce the pressure; Internal leakage makes the oil enter the water tank, the cooling 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 set pressure of the pressure limiting valve is too low.

In the lubrication system, the oil pumped by the oil pump must maintain an appropriate pressure before reaching the lubrication part of the engine. If the set pressure of the pressure limiting valve is too low, the pressure adjusting spring softens or the sealing surface leaks, the set pressure will be too low. At this time, the pressure limiting valve should be adjusted to make the pressure return to normal.

9. Improper brand of engine oil

Different engines need to add different brands of engine oil, and the same type of engine should also choose different brands of engine oil in different seasons. If the selected engine oil is unsuitable or inferior, the leakage will increase and the pressure will decrease due to the low viscosity when the engine is running. Oil should be selected correctly and reasonably to adapt to different models or seasons.

10, pressure sensor failure or oil circuit blockage

If the pressure sensor fails or the oil path from the main oil path to the pressure sensor is blocked and the oil flow is not smooth, the oil pressure will drop. The following inspections can be carried out: idling the engine, loosening the oil pipe joint, observing the oil flow, judging the fault location, replacing the pressure sensor or cleaning the oil circuit.

1 1, oil filter is blocked.

When the oil filter is blocked and cannot circulate, the bypass valve on its base is opened, and the oil directly enters the main oil circuit without filtering. If the opening pressure of the bypass valve is set too high, when the oil filter is blocked and cannot be opened in time, the pressure of the oil pump will increase, the internal leakage will increase, the oil supply of the main oil circuit will decrease, and the oil pressure will drop. Ensure the cleanliness of the oil filter; Correctly adjust the opening pressure of the bypass valve, replace or repair the damaged parts or mating surfaces in time, and restore its normal working performance.

12. The fit clearance between the main bearing and the connecting rod bearing increases.

After the engine is used for a long time, the fit clearance between the main crankshaft and the connecting rod bearing gradually increases, the leakage increases and the oil pressure decreases. For every 0.0 1 mm increase in mating clearance, the pressure will decrease by 0.0 1 MPa. At this time, the crankshaft can be ground, and new connecting rod bearings and main bearings can be selected to restore their fit clearance.

Through the above analysis, we rushed to the construction site with the oil pressure gauge and oil quality analyzer, and tested the quality of the oil with the oil quality analyzer, and found that the viscosity and pollution degree of the oil met the requirements. Connect the oil pressure gauge to 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 conditions, lower than 0. 15MPa at low speed and lower than 0.6MPa at high speed, which shows that the oil pressure is low and cannot reach the normal pressure. We check the bypass valve on the oil filter seat according to the principle from simple to complex and from outside to inside. After disassembly, we found that the seal between the steel ball and the valve seat was not tight, which led to oil leakage and pressure reduction. By grinding the sealing surface, the sealing performance is restored, the pressure is adjusted to the standard value, and the oil pressure alarm lamp goes out, indicating that the machine is back to normal and the fault is relieved.

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