First, the inspection and evaluation of the condition of engine components.
1. Inspection and assessment of the plunger's technical condition
(1) Visual inspection: Examine the most worn areas of the plunger. If you can feel a distinct groove with your fingernail when running your finger across it, the plunger should be replaced with a new one.
(2) Empirical testing: Clean the plunger with diesel fuel and fill the sleeve with diesel as well. Block the oil inlet, return, and center holes with your fingers, then pull out the plunger. After pulling it out about one-third of its length, release it. If it returns immediately, it is still functional; otherwise, replace it.
(3) Pressure gauge method: Connect a pressure gauge to the pump head, set the throttle to maximum fuel supply, engage the decompression mechanism, and crank the engine so that the plunger pumps oil at 30 cycles per minute. The pressure must exceed 19.6 kPa. If not, the plunger needs to be replaced.
2. Checking and evaluating the condition of the fuel valve
(1) Visual inspection: Check the sealing ring. If it is recessed or its width exceeds 0.5 mm, or if the decompression band shows obvious wear marks and the original bright surface is no longer visible, the part should be replaced.
(2) Oil pressure test: Remove the high-pressure fuel line of the cylinder being tested, open the injection pump inspection cover, move the plunger to the bottom dead center, and use the hand pump to purge air from the system. Then check for leaks at the high-pressure pipe joints. If any leakage is found, replace the component (this method does not test the decompression ring).
(3) Pressure gauge method: This should be done simultaneously with the plunger pressure test. When the pressure drops from 19.6 kPa to 17.65 kPa, observe how long it takes for the pressure gauge pointer to stabilize. If it stabilizes within 15 seconds, the seal is good. If the pressure reaches 24.52 kPa and then drops back to 0.98–6.87 kPa, the decompression is normal. Only with a good seal can the exact rebound value be measured.
If faults persist after these checks, remove the fuel valve, clean it, and inspect for wear. If there are no significant grooves, the high-pressure copper washer may not be damaged. Usually, after cleaning and tightening, the seal will return to normal. Otherwise, replace the component.
3. Inspection and evaluation of the fuel injector’s technical condition
This inspection should only be performed after confirming that the plunger pair and outlet valve are functioning properly.
(1) In-vehicle testing: When other engine components are in good condition, install the fuel injector after basic adjustment. Start the engine and listen for sound and observe the exhaust for signs of proper operation.
(2) Standard nozzle comparison: Use a standard nozzle that has been pre-adjusted to compare with the one under test. Connect both nozzles in parallel to the fuel pump via a three-way pipe. Purge the system, set the throttle to maximum, and observe whether both nozzles spray at the same time. If they do, the tested injectors are likely working correctly.
(3) Pressure gauge test: Connect the pressure gauge and the injector in parallel with the fuel pump using a tee fitting. Set the throttle to maximum, engage the decompression lever, and pump oil until the pressure reaches 9.8 kPa. The injector should spray approximately 10 times per minute without dripping. After adjusting the needle valve to the specified pressure, perform an atomization test at around 80 cycles per minute. The droplets should be fine, evenly distributed, and the oil jet should have the correct cone angle and crisp cut.
If problems remain after these tests, disassemble the needle valve, plunger, and spring for cleaning and inspection. If serious wear prevents normal function, replace the parts.
Second, extending the life of the coupling components
In addition to product quality issues, the main cause of coupling failure is improper machine use and incorrect maintenance. Here are some measures to help extend the service life of the couplings.
1. Strictly follow the fuel filtration system. Diesel should be stored for at least 48 hours before use. Ensure the fuel meets seasonal standards, and keep all refueling tools clean. Keep the refueling and storage areas clean to prevent dirt from mixing with the fuel, which can accelerate coupling wear and shorten its lifespan.
2. Establish strict maintenance procedures. Replace the fuel filter every 100 hours and the fuel tank every 500 hours. If the filter element is damaged, replace it immediately—never bypass it. Inspect the coupling every 500 hours of operation. During disassembly, ensure the work area, hands, tools, and cleaning oil are all clean to avoid contamination. Avoid tapping during disassembly and do not throw away parts carelessly. Do not wash them with other components to prevent damage. During assembly, do not change positions arbitrarily. Tighten the fuel valve seat and nozzle cap to the specified torque to ensure proper function.
3. Improve understanding of dual-part systems. Learn the structure and working principles of each component. Strengthen maintenance, operation, and usage practices. Avoid unnecessary adjustments or disassemblies. Do not randomly knock, clean, or rub parts. Avoid changing screw positions during assembly. Always follow technical specifications to ensure the longevity of the components.
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