The reliable operation of the high-pressure oil pump depends on the clearance between the plunger and the guide sleeve. Usually, the radial clearance between the plunger and the guide sleeve is only a few microns. If the clearance is too large, excessive fuel leakage will result. Causes the diesel engine to become misfiring and even causes difficulty in starting.
Case 1: The WCB is a Panamax bulk carrier, the model number of the host is MITSUBISHI UEC45LA, the maximum speed is 158 rpm, the indicated power is 5,295kw, the total running time of the host is more than 63,800 hours, and the high pressure oil pump also has more than 20,000 hours. Maintenance and repair. When the ship arrived at the Port of Portland in the United States, the main engine decelerated and tested. As a result, it was found that the discharge temperature of each cylinder was very different and the speed fluctuation was significant. The main engine is stopped. After the ship speed is lowered, the main engine is started again. However, it is difficult to start the operation in the central control room, and it is urgently converted to the side of the aircraft to operate the car. The throttle can be increased to start the operation, and the operation is maintained until the good anchor is thrown. During the use of the motor vehicle, it was confirmed that the high-pressure fuel pipe pulse of two cylinders became weak; the leakage of the high-pressure oil pump (bottom valve pump manufacturing technology) at the observation hole at the bottom of the body increased. Why all the high-pressure pump plungers and bushings wear out so quickly that the analysis is likely to be related to the 650 tons (380cst at 50 °C) fuel oil installed in the port of San Francisco, USA (according to the laboratory spectral analysis, that fuel The spectral characteristic curve is not fuel, much like the hydraulic oil composition.) Fuel containing a large amount of hydraulic oil, when heated to about 130°C, the lubrication performance is poor, so the continuous use of the fuel is less than twenty days, resulting in a high-pressure pump Plunger and guide sleeve fittings wear rapidly to varying degrees. The disassembled high-pressure oil pump found that most of the plunger surface has turned black (normally bright) and the radial clearance has exceeded the limit value. All the high pressure oil pump plungers had to be renewed. After the new ones, although the difficulties of starting up were solved, the speed fluctuations of the main engine were still large at low speeds. This problem continued for more than six months.
We reviewed all the records of the overhaul of the high pressure pump, corrected the timing of the fuel supply to the high pressure oil pumps of each cylinder, approved the calibration of the throttle rack, and removed the injectors of each cylinder from the pump pressure test, inspection, etc., but the problem still exists. . The final decision was made to fully inspect the sealing of the high-pressure pump. The results showed that when the high-pressure pump was not closed, the high-pressure fuel line was removed and a large amount of fuel overflowed. This caused the leakage of the high-pressure pump outlet valve. Because when the host stops, the high-pressure pump plunger does not move, the pressure in the pump chamber drops, and the outlet valve should be able to close automatically under the action of the spring pressure. The outlet valve with good condition will not leak. The valve plug and the valve seat of the high pressure oil pump outlet valve are cone-surface sealed. The closing seal is effected by the spring on the top of the valve body. Because of long-term operation and repeated impact, the bad marks are worn on the tapered surface of the valve core. It caused an internal leakage in the high-pressure pump. Especially at low speeds, the internal leakage is even worse, the fuel supply is different, the load output of each cylinder is uneven, and the rotational speed fluctuates. The difference in the exhaust temperature of each cylinder is also large. After replacing the outlet valve or spring of the four cylinders, the main engine is operating normally.
Therefore, in the daily management, carefully observe the changes in the performance of the high-pressure pump, you can find the symptoms that cause the failure:
(1) Changes in the efficiency of the high-pressure oil pump: High-pressure oil pumps with good performance, generally 1 to 2 grids with single-cylinder racks, explosive pressure in the cylinder, and exhaust gas temperature will change significantly. Otherwise, the plunger of the high-pressure pump should be considered, whether the guide bush is worn or not, and whether the oil valve leaks.
(2) Observe the change of the scale of the throttle at the same speed from the scale of the control panel of the total throttle joystick, taking into account the difference in the oil supply of the high pressure oil pump, so as to grasp the working efficiency of the high pressure oil pump.
(3) From the observation hole (tube) at the bottom of the high pressure oil pump body, the change of the oil leakage can be observed, and the sealing condition of the high pressure oil pump plunger couple can be further judged.
(4) When running at low speed, the working efficiency of the diesel engine can be more inspected. When the engine runs at low speed, the changes in the parameters of each cylinder are measured and recorded. If the internal leakage, the explosion pressure decreases, and the compression pressure does not change.
(5) When the diesel engine is in operation, the hand feels high pressure tubing feels weaker pulses, indicating serious internal leakage.
(6) When the diesel engine is running, the high-pressure oil pump body generates heat, and the internal noise of the pump can be heard to be large, which indicates that the internal leakage is serious.
(7) The top of the piston will be found when the cylinder is hoisted. The carbon in the combustion chamber at the upper part of the cylinder liner is severe. Excluding the reason for the injector, it shows that the internal leakage is serious and affects the atomization of the fuel.
High-pressure pump inlet valve for MAN-BWMC, MCE, MCS and other models is designed with a conical seal. An automatic slide valve is built into the valve housing of the inlet valve. As the oil pressure in the pump rises, the pressure is decreased when the pressure drops. Under the effect of closing, sealing, but the long-term reciprocating action will make the slide valve and valve seat wear between the slide valve movement stroke becomes larger (travel limit is generally required around 0.5mm), the gap is too large must be renewed. Such as MAN-BWMC models, the inlet valve and the release valve are combined together. When the host requests a stop, the release valve, under the action of safe air, pushes the small piston downward to open the inlet valve. Although the inner plunger moves up and down, the hydraulic pressure in the high-pressure oil pump cannot reach the valve opening pressure of the injector, and the by-pass function does not spray the fuel into the cylinder, thereby promptly stopping the engine. However, due to the leakage valve is not often action, coupled with the viscosity of the fuel, often there will be a small piston stuck in the leak valve, causing the phenomenon of not open or close. Therefore, it is necessary to turn off the safety air when it is parked. Remove the upper end cap and use a special screw to screw up and down, or periodically remove it and clean it with kerosene, and check the condition of each sealing ring. In addition, the long-term wear of the valve seat and the valve seat can also cause the upper part of the inlet valve head to always contact with the piston in the drain valve, so that the relief valve is always open, and the fuel cannot be sprayed through the injector. Into the cylinder. Therefore, there must be a gap between the upper part of the valve head and the plunger (more than 0.1mm), and if it is less than the limit, it must be replaced.
Case 2: The OCEANC mainframe model is MAN-BW6L50MC. There is always a single cylinder in the maneuvering operation will not get angry, when the hand touch the high pressure tubing no pulse, the cylinder exhaust temperature is very low (compared to the normal working cylinder), The high pressure oil pump is shown without injection. Check the relief valve on the upper part of the high-pressure pump. The drain valve works normally. When the rotation speed increases, the high-pressure fuel pipe of the cylinder pulsates again, and the exhaust temperature of the cylinder also rises. Repeated inspections, this failure still exists, bringing hidden dangers to the safe operation of the ship. For this reason, we completely disassembled the high-pressure oil pump and checked, measured, and compared one-by-one parts that had not been replaced before. The final question is the failure of the suction valve. From the appearance of the suction valve valve head and valve seat contact surface, although the spring is intact, there is no damage, but the spring of the suction valve is found to be higher than the new suction valve. The spring is soft. According to the working principle of the oil suction valve, when the plunger of the high pressure oil pump rises, the oil pressure and the tension of the spring cause the suction valve to close. The fuel passes through the drain valve, the high pressure oil pipe, and the fuel injector is injected into the cylinder.
When the spring tension of the oil absorption valve is insufficient, when the plunger of the high pressure oil pump goes up, the oil absorption valve cannot be closed, and the fuel returns to the oil inlet pipe of the high pressure oil pump through the oil absorption valve. The fuel cannot generate high pressure to overcome the valve opening pressure of the injector and spray into the cylinder. As a result, single cylinders often do not get angry. Based on the above conditions, we also dismantled the high-pressure oil pump suction valves one by one, replaced the springs in the poor suction valve, and the host finally resumed normal operation. Therefore, for this type of high-pressure pump plunger and guide sleeve parts, drain valve and inlet valve unit should be dismantled and cleaned regularly to ensure the normal operation of the high-pressure pump.
The structure of the return valve type high-pressure oil pump is more complex, and management should have higher requirements. If a wheel host is SULZERRTA68 type, the high pressure oil pump always adjusts the return valve. When the total running time is more than 40,000 hours, it is found that when the main engine runs at low speed, the working condition deteriorates. When checking and adjusting the high pressure oil pump, It was found that there were abnormalities in the outlet valves and drain valves of individual cylinders; there was wear on the seats and valve pressure bearing surfaces; there were corrosion pits on the seat ring's circumferential neck ring and seat surface; the upper pressure sleeve was loosened. Then all worn parts were renewed and re-adjusted. When the original inbound and outbound main engines operated at low speed, the cylinder exhaust temperature was low, and the temperature difference between the cylinders was large, and the problem of rotational speed fluctuations was eliminated. Measured and compared with the parameters before demonstration and further inspection, further analysis found that the explosion pressure increased, the ignition point also changed slightly, the host conditions greatly improved.
In order to avoid the above failures, the following aspects should be done in daily management work:
(1) Regularly inspect parts. According to the overhaul period of different types of high-pressure oil pumps (recommended by the manufacturer), inspections should be carried out gradually. The diesel engine for the old ships should be shortened appropriately (8,000h is appropriate).
(2) Maintain proper fuel inlet pressure, temperature, and a certain return oil back pressure.
(3) Strengthen the separation and purification of fuel and reduce the abrasive metal and moisture in the fuel so as not to cause cavitation.
(4) To continuously lubricate the high pressure oil pump rack and ring gear, it is necessary to adjust the proper amount of oil and not to cut off the oil.
(5) When changing to light oil, touch the pump of the high pressure oil pump to check for changes in temperature; listen to the sound especially at low speeds.
(6) Special attention should be paid to the running-in condition of the internal moving parts of the high-pressure oil pump. The diesel engine has a relatively long stopping time. Before start-up, it is necessary to drive the car so that the high-pressure oil pump and its driving device can be fully lubricated.
(7) Especially when the machine is still in the maneuvering state, it still uses the heavy oil (do not perform light and heavy oil conversion operation), and should keep the fuel booster pump and the circulating oil pump running under proper pressure while parking, and whether the pump body of the high pressure oil pump is hot enough In order to understand the status of each valve element in the pump and the fuel cycle conditions.
(8) Keep the fuel pipeline and the pump body in good heat trace, effectively package the thermal insulation material, and avoid the oil temperature drop caused by the direct blown vents.
(9) Manually pump and refuel the high-pressure oil pump after inspection. Otherwise, the short-term operation under the oil shortage condition will cause the high pressure oil pump to dry and scrap.
(10) For high-pressure oil pumps equipped with VIT variable timing mechanism, VIT mechanism has two methods of total reconciliation and monotonicity, which is adjusted by a single cylinder to maintain the appropriate explosion pressure of each cylinder when the load changes; the VIT rack is often cleaned to prevent The VIT mechanism loses its function due to the seizure caused by the oil leakage between the plunger and the guide sleeve.
(11) The shock absorber of the high-pressure pump often leaks due to wear of the SEAL-RING. During the inspection, it is found that there is leakage of oil in the leak detection hole (tube). It is necessary to dismantle and replace the SEAL-RING in time. (12) High-pressure oil pump, When the lower leak detection hole (tube) leaks, it indicates that the O-ring on the sleeve of the high-pressure pump has been damaged and must be replaced in time.
In short, in the usual management, we need to check more, find out as soon as possible, deal with problems in a timely manner, and be careful, careful, and dedicated. The high-pressure oil pump works in the best condition to ensure the normal operation of the diesel engine.
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