What are the functions of the pressure limiting valve, safety valve and return valve in the engine lubrication system?
1.Pressure limiting valve
In order to prevent the high oil pressure of the lubricating system from increasing the power consumption of the engine and causing 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 to not exceed the specified value. Its working principle is that when the oil pressure in the oil circuit of the engine lubricating system exceeds the specified value, the pressure limiting valve is pushed open, and the excess lubricating oil flows back to the oil sump or the oil inlet of the oil pump, so as to reduce the oil pressure. The higher the oil pressure, the greater the opening of the pressure limiting valve, the more lubricating oil flowing back to the oil sump, 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.
2.Safety valve
When the engine is working, if the primary oil filter is seriously blocked by impurities, or the oil viscosity becomes higher due to low temperature, the main oil passage will be short of oil, and the engine will lose lubrication. This is very dangerous, especially for the main bearing and connecting rod bearing. If there is no lubricating oil, the bearing alloy will be burned out due to friction and heat, and even fused with the journal, finally forcing the engine to stop working. In order to avoid the above undesirable phenomena, a bypass valve (safety valve) in parallel with the primary filter is installed in the lubrication system. When the primary filter is blocked and the pressure difference between the 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 dirty, the engine will not lose necessary normal lubrication due to lack of lubricating oil, preventing dry friction.
3.Return valve
It is a liquid pressure control valve, also called overflow valve. It can play a certain role in safety protection and constant pressure overflow for the hydraulic device of the vehicle. The return valve is in the throttling regulating system of the constant displacement pump, which mainly provides constant flow. It can be adjusted according to the flow. If the system pressure increases, the flow demand will be reduced. When the overflow valve is opened at this time, the excess flow will overflow to the oil tank, thus ensuring the constant pressure at the inlet of the overflow valve.
Function of return valve
a. Steady pressure. When the system works normally, the valve is closed. Only when the load exceeds the specified limit (the system pressure exceeds the set pressure), can the overflow be opened and the overload protection be carried out so that the system pressure will not increase (usually the set pressure of the overflow valve is 10%~20% higher than the maximum working pressure of the system).
b. Unload the load. The remote control port of the return valve is connected in series with the solenoid valve with small flow. When the solenoid iron is energized, the remote control port of the return valve is connected to the oil tank, and the hydraulic pump is unloaded. The return valve can unload the load at this time.
Stabilize components. The return valve is connected in series on the return circuit. If the return valve produces back pressure, the moving parts will be stabilized at that time.
