17
2025
-
07
Truck Encyclopedia (9): Expansion water tank, a lot of things
Today, we will talk about the expansion tank in the engine cooling system.
It is said that since the last time Lao Wang bought a new car, he has taken care of it wholeheartedly, and he has to check the engine oil, brake fluid and coolant before leaving the car every day, and make up for the lack of a little as soon as possible.
On this day, Lao Wang found that there was a bit of a shortage of coolant in the expansion tank, so he was ready to replenish it, and Lao Li happened to be next to him, seeing that Lao Wang filled the expansion tank directly. Lao Li hurriedly stopped Lao Wang, the coolant can't be filled!
But why can't it be filled? This has to start with the principle of the expansion tank.
▎ Its appearance is not good, but it has great connotation
The expansion tank usually has 1-2 interfaces at the top and bottom of the tank depending on the model.
The interface, located at the top of the tank, is mainly used to collect the air in the engine cooling channel and the cooling tank. These two thin tubes connect the engine water circuit and the top of the cooling tank, respectively. When air is mixed into the heat dissipation system, these two thin pipes are discharged into the expansion tank.
The water nozzle, located at the bottom of the tank, is used to replenish the cooling system with coolant.
In this engine, for example, the two pipes (shown in the dotted line) are connected to the top of the cooling tank and the engine circuit, from which the air in the cooling system flows back into the expansion tank.
During the small cycle, excess air is discharged from the engine exhaust channel, and during the large cycle, part of the coolant is also circulated there.
When the large circulation, the exhaust channel on the cooling tank discharges.
(The above refers to the design under normal circumstances, and the design of different models is different)
The working principle is explained clearly, then the role of the expansion tank is easy to say.
● Water and gas separation, pressure balance
The main components of the coolant are glycol and water, so when the engine is working, a small amount of steam is generated in the cooling system, and the pressure of the cooling system is constantly changing with the change of water temperature.
If the vapor cannot be discharged and circulates in the cooling line, it will cause air resistance in the heat dissipation line, resulting in poor heat dissipation and an increase in water temperature.
With an expansion tank, steam from the radiator and engine waterways can be separated and stored to equalize the pressure on the system.
However, the gas can be compressed, the coolant cannot be compressed. Therefore, the expansion tank cannot be completely filled, and the liquid level height cannot be higher than the upper limit of the expansion tank when the coolant is filled.
When the engine cylinder vibrates, bubbles are formed in the coolant and water hammer (a phenomenon in which the pressure fluctuates greatly due to a sudden change in the flow rate of a liquid in a pressurized pipe).
Under repeated action, the outer surface of the cylinder liner is fatigued and gradually falls off, showing pitted and needle-like holes, which is cavitation.
The separation of water vapor from the expansion tank can reduce the occurrence of cavitation. In addition, under the replenishment of the expansion tank, thus reducing air mixing.
Therefore, the expansion tank should not be too short of coolant, and the coolant level height should not be lower than the lower limit of the expansion tank.
● Ensure the pressure of the heat dissipation system, and also relieve the pressure safely
The lid of the expansion tank is also very good, in addition to sealing, the expansion tank cover of some models also has the function of relieving pressure. (Whether the lid has a pressure relief function depends on the manufacturer's design and does not indicate the quality of the engine.) ）
Lid with pressure relief
Pressure relief is when the pressure of the heat dissipation system is too large, such as the phenomenon of boiling the pot, the pressure relief valve of the lid will be opened, and the system pressure will be discharged in time to avoid serious losses.
Lid with a sealing function only
The sealing is to establish a certain pressure, increase the boiling point of the coolant, and improve the performance of the coolant.
In addition, the expansion tank also allows the driver to check the quality of the coolant's life and visually observe whether there is a lack of coolant inside.
In addition, more and more trucks are now equipped with liquid level sensors in the expansion tank, which can prompt the driver in time through the dashboard when the coolant is empty, so as to avoid the phenomenon of "boiling the pot" due to lack of coolant.
After reading today's introduction, I believe you know how this inconspicuous expansion tank escorts our cooling system. Automotive design is a very rigorous discipline, and any component has its value. There are many ingeniously designed components such as the expansion tank in the vehicle, and the old driver's class will be revealed one by one in the future.
Focus on the research and development of automotive brake systems and pneumatic brake valves to promote the development of the auto parts industry!
Contact Information
Telephone:86-575-87438928
Mobile:8613252110178
QQ：1185450863@qq.com
Address: No. 461, Advanced Village, Fengqiao Town, Zhuji, Zhejiang Province
Online message
Submit your information and we will contact you as soon as possible.