When it comes to the quality of oil filters, many people first think of filter paper. Indeed, for some environmentally friendly oil filters, the quality of the filter paper directly affects the filtration efficiency of the oil filter. However, for rotary mounted oil filters with shells, filter paper is not the only factor that measures the quality of the oil filter. This type of oil filter usually has two key components, one is a bypass valve and the other is a check valve.

Bypass valve
As the name suggests, a bypass valve is a valve that is usually closed. All oil needs to pass through the filter paper to obtain sufficient filtration. However, if the following two situations occur, the bypass valve will open and unfiltered oil will directly enter the lubricating oil passage.
One is when the oil filter is severely blocked, and the other is when the oil is very viscous (cold starting at low temperature). Both of these situations will make it difficult for the oil to pass through the filter paper, resulting in insufficient lubrication flow. At this point, the bypass valve opens due to the increase in pressure on the outside of the filter paper, which is actually a protective mechanism for the engine, because compared to unfiltered oil, insufficient lubrication flow poses a greater risk, which is the lesser of the two hazards.
During low temperature cold starting, the bypass valve only needs to be opened for a short period of time after starting the engine. As the engine temperature increases and the oil viscosity decreases, the bypass valve will close, so the impact on the engine is not significant.
When the machine filter is severely blocked, it will cause the bypass valve to remain open, which will cause a continuous flow of unclean oil into the lubricating oil channel, and its harm can be imagined. Therefore, timely maintenance of vehicles and avoiding the use of inferior engine oil have become particularly important.

Check valve
A check valve is usually installed on a machine filter with the inlet and outlet facing downwards. Its function is to prevent the oil in the machine filter from flowing back under the action of gravity after the engine is shut down. Because if there is no oil in the filter, the oil pump needs to first fill the filter every time the engine is started, which will cause the oil pressure to build slowly and exacerbate cold start wear. With a check valve, a certain amount of oil will always be retained in the engine filter, so that oil pressure can be quickly established when the engine starts.

Through the above introduction, I believe everyone has understood that the bypass valve and check valve, two key components, directly affect the quality of the oil filter. If these two valves are not effective, the filter paper of the oil filter will be useless. Therefore, when purchasing oil filters, we must choose products from legitimate channels. Poor quality oil filters not only have poor filtering media, but also cannot guarantee the working performance of the bypass valve and check valve, Some even do not have bypass and check valves, which can cause significant harm to the engine.