【Meiruier FIlter】The common sense of the oil filter- bypass valve

The significance of the by-pass valve of the filter
Checking the index of the oil filter performance, apart from the filter’s filtration efficiency, the pressure loss that the filter for the system is also important. There must be by-pass valve for the full flow type of oil filter and there is no need for diesel filter. So the performance of the by-pass valve affects the filtration efficiency of the oil filter and pressure loss for the system. 

 If the structure design and production of the by-pass valve is not reasonable, it mainly reflects below:
1.The opening pressure is over low or the sealing of the by-pass valve is not good, which can lead to the low filtration efficiency and even cause the element lose efficiency. 
2.The smaller valve port of the by-pass valve and the higher opening pressure can lead to the high pressure loss and it will eventually affect the engine’s performance.  The fundamental reason of this problem is that the unreasonable design and calculation of the filters’ by-pass valve. 

The working principle of the by-pass valve of the filter
Normally the by-pass valve of oil filter is closed. When the pressure drop of the element is too high, it will provide enough oil( this oil is not filtrated) to different parts of the engine through transporting and splashing, which can have the function of lubrication and cooling and then takes away the heat and metal impurities. When the engine starts in cold state( the viscosity of the oil is high) or the element is blocked, the flow cannot meet the requirement of the engine, then the by-pass valve open and work. 
The by-pass valve is in parallel with filter in the lubrication system. There are two forms of placement: one is inside of the filter, the other is in the assembly, which is located in the port of filter opening and the oil unloading is interlinked with the oil-out. 

The opening pressure of the by-pass valve
The opening pressure is confirmed with needs or the OEM requirements, which should meet the requirement of the filter’s lifetime. 
The opening pressure should not be too low. If it is too low, the oil amount which is not filtrated and come to the oil path will increase, so the impurities will probably come to the friction pair and accelerate the wearing of the parts . 
The original resistance is usually from several KPa to 25KPa, some can be 30kpa, the lifetime of the filter’s pressure drop is 70kpa, when it is lower than the pressure drop of the lifetime, the by-pass valve should not open. Unless the viscosity of the engine is too high, it can be open for the time being. So for the opening design of the by-pass valve, the lifetime pressure drop should not be lower than 70kpa. 

But the opening pressure should not be higher
1.The opening pressure drop is based on not damaging the element. The strength of the element is decided by the filter paper and folding structure. Normally it cannot bear more than 300Kpa-400Kpa, it will be shriveled or blocked when it is over the pressure. 
2.When the opening pressure is too high, the oil supply pressure is low in the main oil gallery. 
When the cold start or the filter element is blocked by the impurities and the opening pressure is too high, the oil cannot be transported to the diesel engine timely, which cause the decreasing of main oil path. If the oil supply pressure is continuously low, it will lead to burning tile and bent axle when seriously. In order to ensure the normal work of the lubrication system, when through rated flow, the resistance should not be more than 200Kpa.