Causes, Fault Phenomena and Complete Solutions of Oil Circuit Air Intake for Diesel Generator Sets with Base Integrated Fuel Tank

2.3 Seal Air Leakage of Filter and Low-pressure End of Fuel Transfer Pump

• Aging or incompletely compressed upper and lower sealing gaskets of primary and fine diesel filters, with gaps easily left after filter replacement
• Worn piston sealing gaskets of the manual fuel pump with poor pressure retention, soft pressing feel and immediate rebound, causing continuous air backflow
• Damaged or loose sealing gaskets at the oil inlet joint of the high-pressure oil pump

2.4 Air Backflow via Oil Return Pipeline

Excess diesel fuel from engine operation flows back to the base fuel tank through the oil return pipe. If the oil return pipeline has loose joints or cracked pipes, the oil circuit will release pressure after unit shutdown, and air will flow back into the entire fuel supply system through the oil return channel, resulting in recurring faults on restart.

3. Typical Fault Phenomena of Oil Circuit Air Intake (Quick Self-inspection)

The air intake fault can be quickly judged through unit operating status without professional equipment:

1. Abnormal manual pump feel: Soft and resistance-free pressing, immediate rebound after pressing, failing to build oil pressure
2. Continuous bubbles during air bleeding: Persistent foam and bubbles overflow from the filter vent screw, with fault recurrence shortly after bleeding
3. Abnormal start-stop conditions: Difficult cold start, easy stalling under hot state, unstable idling and rotating speed
4. Poor load capacity: Normal no-load operation but frequent speed drop and automatic stalling under heavy load or climbing conditions
5. Recurring faults: Air bleeding is mandatory for restart after long-term shutdown

4. Standard Oil Circuit Air Bleeding Procedures (Universal for Base Tank Units)

Preparations before bleeding: Refill diesel fuel to medium or high level, tighten the fuel tank cap, and ensure the top vent valve is unblocked.

Step 1: Primary Bleeding (Primary & Fine Filters)

Loosen the top vent screw of the diesel filter by 2-3 turns, and repeatedly press the manual fuel pump. Stop pumping and tighten the vent screw immediately when continuous bubble-free pure diesel flows out, completing filter section bleeding.

Step 2: Low-pressure Chamber Bleeding of High-pressure Oil Pump

For models equipped with a special vent bolt on the side of the high-pressure oil pump, loosen the bolt and repeat manual pumping until all internal bubbles are removed, then tighten the bolt. Skip this step for models without an independent vent port.

Step 3: Complete Bleeding of High-pressure Fuel Pipeline of Injectors (Mandatory for Stubborn Faults)

For recurring and intractable air intake faults, loosen the fuel inlet nuts of each cylinder injector one by one, start the motor for 3-5 seconds briefly, and tighten all nuts sequentially after bubble-free pure diesel flows out, so as to completely remove air from the high-pressure oil circuit.

Bleeding Qualification Standard: The unit starts successfully at one time with stable idling without jitter, and no stalling or speed drop under load.

5. Permanent Rectification Solutions for Recurring Air Intake Faults

Simple air bleeding only solves temporary problems. Permanent fault elimination relies on repairing all air leakage points with the following key rectifications:

1. Replace all negative pressure pipeline seals: Renew all suction oil pipes, sealing gaskets and stainless steel clamps to eliminate micro-leakage and air suction, the core solution to recurring air intake.
2. Inspect and repair the tank vent system: Unblock blocked vent valves and replace damaged ones; equip complete fuel tank cap sealing gaskets to balance tank air pressure and avoid negative pressure air suction.
3. Check internal tank structure: Drain the tank diesel and open the access cover to inspect and repair cracked or fallen internal suction pipes and filter screens.
4. Standardize daily fuel use habits: Avoid long-term low fuel level operation and keep the tank more than half full to prevent air suction from emptying.
5. Repair tank leakage points: For welding pores and cracks on the base, empty the diesel, fully ventilate for explosion prevention, and repair and seal the defects via argon arc welding.
6. Replace aging pump parts: Replace the manual pump or fuel transfer pump assembly directly in case of severe pressure loss and failure to maintain pressure to avoid continuous air backflow.

6. Field Emergency Solutions (Rush Repair Without Spare Parts)

The following methods can relieve faults temporarily and ensure unit operation during field work with no spare parts available:

• Maintain a high fuel level all the time to reduce negative pressure air intake probability
• Manually bleed air and build oil pressure via the manual pump before each restart after shutdown
• Wrap raw material tape around all oil circuit thread joints to enhance sealing and slow down air intake

Conclusion

90% of oil circuit air intake faults of base tank diesel generator sets are not caused by accessory damage, but by pipeline micro-leakage, air pressure imbalance and incomplete sealing installation. Avoid blind replacement of oil pumps and injectors during maintenance. Prioritize inspection of high-incidence points such as suction pipelines, tank vent valves and sealing gaskets. Follow the process of "bleed air first, find leakage later, and rectify fundamentally" to completely solve starting difficulty, jitter and stalling faults.