High Quality Delivery Valve F910 Diesel Engine Spare Parts

The pressure relief ring of the oil outlet valve is a key structure for controlling the residual pressure after the fuel injection is completed. Its wear or failure will cause problems such as injector dripping, engine black smoke, and increased fuel consumption. To determine whether the pressure relief ring needs to be replaced, it is necessary to combine appearance inspection, functional test and fault phenomenon for comprehensive judgment. The specific methods are as follows:

1. Appearance inspection: Directly observe the degree of wear
The pressure relief ring is a cylindrical surface with extremely high precision on the head of the oil outlet valve (matching with the inner hole of the valve seat). Under normal conditions, the surface should be smooth and free of wear. After disassembly, it can be judged by the following details:

Wear marks
Touch the surface of the ring with your fingers. If there is an obvious "step feeling", "groove" or "drawing mark", it means that the ring has been worn due to long-term friction (normally it should be smooth and unobstructed);
Observe with the help of a magnifying glass. If the diameter of the ring surface is reduced due to uniform wear (compared with the new part), or there is rust or depression in the local area, it needs to be replaced.
Exceeding the standard clearance
The clearance between the pressure relief ring and the inner hole of the valve seat is usually 0.001-0.003mm (slightly different for different models, please refer to the manual);
It can be measured with a special gauge (such as a plug gauge). If the clearance exceeds 0.005mm, or when shaking the oil outlet valve, you can feel obvious radial looseness, which means that the ring is seriously worn and must be replaced.

2. Functional test: judge by pressure change
The core function of the pressure relief ring is: after the injection is completed, the ring is separated from the inner hole of the valve seat first, so that the high-pressure oil circuit is connected with the low-pressure cavity, quickly reducing the residual pressure and avoiding dripping of the injector. If the ring fails, the residual pressure will be too high, which can be verified by the following tests:

Injection pump test bench test
On a professional test bench, simulate the injection process and measure the residual pressure after the injection:
Under normal circumstances, the residual pressure should drop quickly to below 5-10bar (refer to the model standard for specific values);
If the residual pressure exceeds 20bar, or the pressure drops slowly (does not drop to the standard value within 10 seconds), it means that the pressure relief ring is poorly sealed or worn, resulting in failure of the pressure relief function.
Simple pressure relief test
After disassembly, turn the oil outlet valve pair upside down, inject diesel into the valve seat, block the oil outlet with your hand and slowly lift the valve head:
When the pressure relief ring just leaves the valve seat, the diesel should flow out quickly from the gap between the ring and the valve seat (smooth pressure relief);
If the oil flow is slow, intermittent, or a large stroke is required to lift the oil out, it means that the wear of the ring causes the pressure relief channel to be blocked or unsmooth, and it needs to be replaced.

3. Fault phenomenon: judge in combination with engine performance
If the decompression ring fails, the engine will usually have typical symptoms, which can be used as an auxiliary judgment basis:

Injector dripping
After the flame is turned off, the injector still drips fuel (observe the tip of the injector nozzle, there are oil beads condensed or dripping). This is because the residual pressure is too high, and the fuel continues to seep out from the injector gap. In severe cases, it will cause difficulty in starting or carbon deposits in the cylinder.
Abnormal combustion
The engine idle speed is unstable, the acceleration is weak, the exhaust pipe emits black smoke (incompletely burned fuel), or accompanied by a "knocking" sound (dripped fuel premature combustion);
Fuel consumption increases significantly (under the same working conditions, fuel consumption increases by more than 10%).
Difficult to start
It takes multiple attempts to start cold, or the idle speed shakes after starting. This is because the residual pressure is too high, resulting in poor fuel atomization and abnormal mixed gas concentration during the next injection.

4. Replacement principle: cannot be repaired, must be replaced as a whole
The pressure relief ring is the core structure of the precision mating parts, and its wear is irreversible:

If any of the above inspections meet the failure characteristics, the oil outlet valve mating parts (valve head + valve seat set) must be replaced, and the valve head cannot be replaced alone or the ring is polished and repaired (it will destroy the matching accuracy and cause more serious leakage);
When replacing, original accessories or accessories that meet the accuracy standards must be selected to ensure that the diameter and roughness of the pressure relief ring of the new part match the valve seat to avoid rapid wear again due to dimensional errors.

The above methods can accurately determine whether the pressure relief ring has failed. In daily maintenance, it is recommended to combine the regular inspection of the injection pump (such as every 100,000 kilometers) with simultaneous inspection to avoid chain failures caused by ring wear, which affects engine performance and life.