Its function is to limit the oil pressure in the high-pressure rail. When the rail pressure exceeds the preset upper limit, the pressure limiting valve will open and then flow the fuel back to the fuel tank to achieve the purpose of pressure relief.
Common rail valve assembly is one of the fuel injector spare parts commonly used in automobile maintenance. With the increasing maturity of diesel common rail system technology, diesel vehicles are favored and chosen by more and more consumers because of their cleanliness, low energy consumption and environmental protection.
There is no doubt that after-sales and maintenance are closely related to common rail diesel vehicles. The industry is also developing in full swing.
How Pressure Limiting Valve Work？
Under normal circumstances, the pressure relief valve is closed and there is no fuel leakage. Only when a fault occurs, the pressure relief valve will be actively or passively opened.
First, the first stage piston is opened, and after the oil pressure in the oil rail drops, the second stage piston opens to achieve a balance between rail pressure and discharge flow, and the limp mode is performed when the rail pressure is stable at low pressure.
At this time, the system will limit the engine output torque to ensure that the high-pressure fuel rail maintains a certain pressure so that the driver can drive the car to the nearest repair shop for repair.
What are the reasons for the Pressure Limiting Valve to open?
There are two situations for the opening of the pressure limiting valve, one is active and the other is passive. If other fault codes appear in the system, the ECU will send a command to force the relief valve to open to protect the engine. Such as rail pressure sensor, fuel metering valve and other faults. In the case of active opening, other fault codes should be resolved first.
If the rail pressure in the system is too high, it will also cause the pressure relief valve to open. Common reasons for passive opening include: failure of fuel metering valve or relief valve, failure of high-pressure pump, blockage of oil return pipe, etc.
Here are some common reasons why a pressure relief valve opens:
High rail pressure
If you see the fault code that the pressure relief valve is open, the first reaction should be caused by the increase of rail pressure. If the rail pressure is too high, the pressure relief valve will be flushed.
The pressure relief valve itself is faulty
Due to the poor quality of the fuel or the high water content, the fuel filter fails for a long time, resulting in the failure of the internal spring of the pressure relief valve, which will cause the pressure relief valve to be open.
Related to ECU
There are many parts that can cause high rail pressure. Most of the sensors are connected to the ECU. When the sensor signal in the right path is abnormal, the ECU opens the pressure relief valve to protect the engine.
Common faults of Pressure Limiting Valve
The common fault of the pressure limiting valve is abnormal leakage or cannot be opened normally. The judgment method is as follows: For the pressure limiting valve of the fuel system, if the following conditions occur:
The engine is difficult to start, and the phenomenon of "lack of cylinder" occurs after starting, and the engine will be turned off when there is a load. ; When using the hand oil pump to pump oil, the resistance is very small; the oil supply cannot keep up, as if there is air, at this time, you should check whether the pressure limiting valve of the fuel injection pump leaks.
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