when the engine is working, if the oil strainer is seriously blocked by impurities, or the oil viscosity increases due to low temperature, the main oil passage will be short of oil and the engine will lose lubrication, which is very dangerous, especially the main bearing and connecting rod bearing. if there is no lubricating oil, it will burn out, the bearing alloy will be lost due to friction and heating, and even fused and welded with the journal, eventually force the engine to stop working. in order to avoid the above adverse phenomena, a bypass valve (safety valve) in parallel with the strainer is set in the lubrication system. when the primary filter is blocked and the pressure difference between the oil inlet and outlet cannot reach a certain value, the bypass valve will be pushed open, and the oil will flow directly into the main oil passage through the bypass valve without passing through the primary filter. at this time, lubrication is primary and filtration is secondary. although the oil entering the main oil passage is not filtered and a little dirty, the engine will not lose the necessary normal lubrication due to lack of lubricating oil, so as to prevent dry friction.
in order to prevent the excessive oil pressure of the lubrication system from increasing the power consumption of the engine, resulting in oil leakage at the sealing connection in the oil circuit, a limited pressure valve is set on the main oil passage or oil pump. its function is to limit the oil pressure of the lubrication system so that it does not exceed the specified value. its working principle is: when the oil pressure in the oil circuit of the engine lubrication system exceeds the specified value, the pressure limiting valve is pushed open, and the excess lubricating oil flows back to the oil pan or the oil inlet of the oil pump to reduce the oil pressure. the higher the oil pressure, the greater the opening of the pressure limiting valve, the more lubricating oil flows back to the oil pan, and the more the oil pressure drops. when the oil pressure of the lubrication system drops to the normal pressure, the pressure limiting valve will reset under the action of the spring.
the oil bypass valve and oil pressure limiting valve interact and cooperate closely in the process of use, which can achieve the best effect and effectively improve the working efficiency of the engine!