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Trouble analysis and elimination of air intake in the oil circuit system of diesel generators

Trouble analysis and elimination of air intake in the oil circuit system of diesel generators

Once air enters the fuel system of a diesel generator, the engine may be difficult to start or run unsteadily, and at worst, it may be anchored in the road.

If there is air in the fuel supply system, the diesel generator will be difficult to start or extremely easy to stall.

Air has great compressibility and elasticity. When there is a leak in the oil pipe from the fuel tank to the diesel generator fuel pump section, air will infiltrate when a leak occurs, thereby reducing the vacuum in this section of the pipeline, weakening the suction of the fuel in the fuel tank, or even interrupting the flow, causing the engine Unable to start. In the case of less air mixed in, the oil flow can still be maintained and is sent from the fuel delivery pump to the fuel injection pump, but the engine may have difficulty starting, or it may self-extinguish after a short period of time after starting.

When the amount of air mixed in the oil circuit is a little more, it will cause several cylinders to cut off the fuel or significantly reduce the fuel injection volume, making the diesel generator unable to start at all.

How to find and stop leaks in the pipeline?

The fuel supply system of a diesel generator is divided into a low-pressure oil circuit and a high-pressure oil circuit. The low-pressure oil path refers to a section of oil path from the fuel tank to the low-pressure oil cavity of the fuel injection pump, and the high-pressure oil path refers to the section of oil path from the plunger cavity in the high-pressure pump to the fuel injection nozzle. In the supply system of the plunger pump, there will be no air infiltration in the high-pressure oil circuit, and there will be leakage points, which will only cause fuel leakage. Find a way to plug the leakage points. Let’s focus on the leakage problem in the low-pressure oil circuit.

Most of the low-pressure oil circuits of the fuel supply system of diesel generators use soft rubber hoses, and the hoses are prone to friction with parts, causing oil leakage and air intake. Oil leaks are easier to find, while damaged air intake somewhere in the pipeline is not easy to find. The following is the method to determine the leakage point of the low pressure oil circuit.

Judging the leakage point method 1: drain the air in the oil circuit, after starting the engine, find the leakage point, which is the leakage point.

Method 2: Loosen the bleed screw of the engine fuel injection pump and use a manual oil pump to pump oil. If a large amount of air bubbles are discharged from the bleed screw, the air bubbles still do not disappear after repeated hand pumping. It can be determined that there is a leak in the negative pressure oil circuit between the fuel tank and the fuel pump. This section of the pipeline should be removed, and then pressurized gas should be introduced and placed in the water to find out where the bubbles are, that is, the leak point.

In addition to the pipeline problems, various gaskets at the pipeline joints will also leak due to improper installation, deformation, aging and damage, etc., and become leaks. Before detailed inspection of the pipeline, these nodes should be checked first. an examination.

The hard oil pipe in the section outside the oil tank is generally less likely to fail. If the leak cannot be found after the above inspection, it can be checked last.

How to get rid of the air in the oil circuit?

Normal method. Use a screwdriver or a wrench to unscrew any vent screw on both sides of the fuel injection pump for a few turns, press the manual fuel pump with your hand until the discharged diesel is continuous, unobstructed, and there is no air bubbles, and a “squeaking” sound is made. Then tighten the bleed screw and press the manual oil pump back to its original position.

If you do not have a suitable screwdriver or wrench to open the bleed screw on the fuel injection pump while driving, you can first unscrew the hand fuel pump, then loosen any pipe joint from the diesel filter to the fuel injection pump, and then repeat Press the hand oil pump until the smooth and bubble-free oil flow is discharged from the joint, and then tighten the joint while pressing the hand oil pump, and then press the hand oil pump back to the original position.

If you don’t have a wrench to loosen the joints in the pipeline, you can press your hand oil pump repeatedly until the pressure in the low pressure oil path from the fuel transfer pump to the fuel injection pump section is high enough, and the fuel flows into the fuel return pipe from the overflow valve. The gas in the oil circuit will be discharged from the overflow valve.

If you need to remove the air from the oil circuit during the journey, you can first loosen the bleed screw on the fuel injection pump or loosen any joint between the diesel filter and the fuel injection pump, and then drive the mechanical fuel transfer pump by starting . The leak point will spray out unobstructed and bubble-free fuel, then tighten the leak point you loosened.

What are the common faults of diesel generator and what are the inspection methods?

What to check when the diesel generator fails to start?

The successful start of a diesel generator must ensure that it has a sufficiently high speed, good cylinder compression force, and timely injection of well-atomized fuel. In addition, there must be a certain temperature to make the atomized fuel reach a fire state.

When it fails to start, check the circuit first. If the start button is pressed and the starter motor does not move, the circuit is broken or the contact is poor. If there is only the sound of the start gear and the flywheel ring gear, the large and small gears have failed to mesh. At this time, just rotate the flywheel by one to a few teeth. If the starter motor becomes weak and the speed is low, the battery power is insufficient.

If the starter motor is running vigorously, the speed is normal and does not ignite, the fuel nozzle is not called, and the exhaust pipe is smokeless, it is a fuel system failure. Or even if it can be started, and the flame is turned off after a few rotations, there is air or moisture in the fuel.

When the starting motor reaches the starting speed, although there is a sound of fuel injection from the nozzle, it is not easy to start and there is a sound of air leakage. After stopping, use a screwdriver to turn the flywheel. If it is weak, or the resistance is small, and the flywheel does not rebound, it indicates that the compression force is insufficient.

If the ambient temperature is too low, or the machine has been parked for too long, the oil is too thick, the resistance of moving parts is large, the gap between the piston and the cylinder is too large, and the compression force is insufficient, it will be difficult to start. At this time, use hot water or steam to preheat the machine before starting.

How to check if the power of 500kw diesel generator is insufficient?

The main feature is that the operation is not stable at low speed, the exhaust pipe emits black smoke at high speed, and the sound is abnormal. In the case that the diesel generator has not reached the overhaul period, the insufficient power is mainly caused by the failure of the fuel supply system and the insufficient compression force of the cylinder.

Check the empty car first. If you increase the throttle and the empty car can reach the maximum speed, the fault lies in the working machinery. If the speed of the empty car does not go up, the fault lies in the diesel generator.

Check the temperature of the root of the exhaust manifold. If the temperature of a certain cylinder is low, the cylinder does not work or does not work well. Fingers can be used for touch inspection at low speeds, but not at high speeds to prevent finger burns. At this time, you can spit saliva to the root of the exhaust manifold. If the saliva does not make a “click” sound, the cylinder is malfunctioning.

Pinch the high-pressure oil pipe with your fingers. If the pulsation is strong and the temperature is higher than other cylinders, it indicates that the oil pump is good, and the fuel injector may be seized in the fully closed position or the pressure of the pressure regulating spring of the oil nozzle is too high; if the high-pressure oil pipe has weak pulsation, the temperature is The other cylinders are consistent, which means that the fuel injector is seized or the pressure regulating spring is broken in the fully open position. If there is no pulsation in the high-pressure oil pipe at high speed and the temperature is higher than other cylinders, it indicates that the high-pressure oil pump is malfunctioning. If the exhaust pipe emits a smoke ring at low speed, it means that the outlet valve spring of the high-pressure oil pump is broken or the gasket is invalid. If the fuel system has no abnormal symptoms, the fault is poor compression of the cylinder.

During operation, if the blow-by gas under the oil filler port increases and the ambient oil smell is strong, the gap between the piston and the cylinder is too large and the seal is not good. If you use a screwdriver to turn the flywheel for two weeks when parking, and the number of times the hand feel resistance increases is not equal to the number of cylinders, you can judge that a certain cylinder has poor compression based on the hand feel. If there is a sound of air leakage at the junction of the cylinder head and the cylinder body, the ambient smoke is thick and there is a smoky smell, it means that the cylinder head gasket is leaking. If there is a metal knocking sound at the cylinder cover, which is related to the speed and is regular, it means that the gap between the rocker arm and the valve is too large. If there is a sound of air leakage at the cylinder head, at low speed, the temperature of the root of the intake manifold is high, and there is a sound of air leakage at the intake pipe when parking, it means that the intake valve is leaking; if the exhaust pipe emits black smoke at high speed, at night Flaming tongue in the exhaust pipe indicates that the exhaust valve is leaking.

What is the reason for the automatic flameout of the diesel generator?

There are many reasons for the automatic flameout, but there are two main reasons: one is the interruption of fuel supply; the other is that the moving parts are blocked.

During normal operation, if the speed gradually slows down, the explosion sound gradually weakens, the water temperature, oil temperature, and pressure are all normal, and pushing the throttle has no effect. After a period of time, it will gradually turn off. After stopping, use a screwdriver to turn the flywheel, it means yes. The fuel supply is poor or interrupted.

During operation, the oil pressure is normal, but the oil temperature is higher, the water temperature is increased, and there is a smell of paint. The cooling water outlet has little or no water, direct steam, the machine is running hard, the noise is rough, and the cylinder is pulled when it is nearing parking. The speed is gradually reduced, and the flywheel is difficult to rotate forward and backward when it is finally stopped, and the flywheel does not move after parking. After the temperature of the engine is lowered, the flywheel can be turned again, and it can be judged that the piston is seized.

During operation, the water temperature is normal, the oil pressure drops, the oil temperature rises, there are metal chips in the oil, the smell of organic oil burns, the vibration of the machine increases, the sound is abnormal, the speed gradually decreases, the inertia rotation time is short when stopping, and the machine stops. The rear plate does not move the flywheel, and the machine does not move the flywheel even after the machine is cooled. It can be judged that the main shaft is burning, also known as shaft holding.