What is an expansion tank cap
Any driver, even the most inexperienced one, knows well what an expansion tank is for in a car. Coolant is poured into it, and the remaining free volume is designed to compensate for an increase or decrease in the amount of expanded liquid.
Accordingly, the tank is closed with a lid. The cover is installed on the neck of the tank in its upper part.
Many drivers do not attach much importance to the lid - after all, it is important to simply maintain the tightness of the reservoir, and it does not matter how exactly to close it
Yes, the expansion tank cap is a locking element. However, contrary to popular belief, the lid has a complex structure and performs special functions.
Lid cavity includes rubber seal and double valve mechanism
What is an element made of?
The lid contains two valves. They are designed to protect the cooling system from possible damage due to overheating, in addition, these valves stabilize the operation of the entire system.
Two valves are plugs of two closing springs
The lid must fit tightly (without gaps) to the edges of the tank. For reliable connection, the sealing gum is included in the composition of the cover. Inside there are two valves:
- the first bleeds excess pressure in the tank;
- the second pumps the necessary pressure into the tank if the pump for some reason does not cope with its work.
These valves got their names due to the use of high or low pressure: on VAZs, the first valve is called a safety valve, and the second is called a vacuum valve. However, both are at rest as long as the pressure in the tank is within the specified reading range.
Valve cover mechanisms on VAZs are springs
Symptoms of a malfunctioning expansion tank cap
Owners of Russian-made cars know how important it is to monitor the condition of all systems in the design of the car. Even such a small element as the expansion tank cap can cause a lot of trouble - for example, if the valve mechanisms fail, the operation of the entire cooling system may be disrupted
As a result - overheating of the motor and jamming of the cylinders. The driver in this case is waiting for an expensive repair.
Therefore, in order to prevent unpleasant consequences, you need to carefully monitor while driving for some features in the behavior of the car:
- puffs of smoke appear from under the hood - therefore, the coolant has hit the hot surface of the intake manifold. Antifreeze could get on the collector for only one reason - the safety valve on the cover failed;
- cool air comes out of the stove, and the engine gets very hot: this is a sign of failure of the cover vacuum valve. Due to malfunctions in its operation, air jams occur in the cooling system, which leads to overheating of the motor;
- breakdowns of clamps, ruptures of hoses also indicate that the pressure in the system is unstable. And since it is the cap of the expansion tank that is responsible for the pressure, these symptoms indicate that it is time to replace or repair it.
If puffs of smoke come out from under the hood, this may indicate a malfunction of the expansion tank cap.
New engines and cover
Now everything is completely different, as I already wrote (link above), the plug is now a high pressure valve. Which works for about from 1.1 to 1.4 ATM
(it all depends on the manufacturer).
How it works?
Yes, everything is simple. The expansion tank plug closes the cooling system, making it airtight. When the coolant warms up, then according to the laws of physics, it expands, the pressure increases accordingly, and since the system is closed, here you have 1.1 - 1.4 ATM
But if the injection continues, the lid should open! IT IS IMPORTANT.
Why is this being done, in the sense of building up pressure? Again, everything is simple - in order for the coolant to boil as high as possible at high temperatures.
BUT WHY SO MUCH?
And here is a simple explanation - often modern engines, such as CHEVROLET, OPEL, BMW, MERCEDES, VOLKSWAGEN, etc., operate at high temperatures. Often at 110 degrees Celsius (CHEVROLET doesn't even have a temperature gauge on the dash, so you don't get shocked)!
They are called - "hot engines"
, this is facilitated by both the design (for example, an increase in the compression ratio, an increase in speed, now it is not uncommon even on ATMO - 6 - 7000), and the installation of TURBINES. And in order not to overheat them, they need to be effectively cooled (this is not an ancient SOD for you), otherwise they will quickly become unusable.
Well, what happens at the end. YES what the expansion tank cap is now part of this complex system. It should control both low pressure and high pressure (so that it does not grow unnecessarily), a little more
Old motors and cork
I would like to say a few words about old engines, and why NOT the expansion tank cap. It’s just that earlier it was on the radiator (not on the tank) - it was nominal (that is, little depended on it). Often, the motors worked at atmospheric pressure, that is, the engine cooling system (ODS), did not need any pressure and sealing (no, maybe there was pressure, but not so much), and they often filled the system with water before, and not .
This happened because the power units used to be with thick walls (often cast iron), they worked at relatively low speeds, and even if at some kind of rise (say in the mountains) your radiator started to soar, then you could just stop and wait until the car cool down and move on. The margin of safety was enormous.
How the coolant reservoir cap works
The cooling system of the internal combustion engine is completely sealed. However, due to the fact that the coolant is made on the basis of methyl alcohol, it can increase in volume during the heating process.
Therefore, excess fluid, as well as compressed air, enter the reserve tank, the expansion tank, when heated. If the air in the system is highly compressed due to an increase in the volume of liquid, then the exhaust valve in the lid is activated: it opens slightly, and excess air comes out.
Further, when the car has been standing for a long time, a reverse reaction occurs: the motor and fluid cool down, due to which the volume of antifreeze is sharply reduced. Accordingly, air jams appear in the system. Thanks to the inlet valve, these plugs are quickly removed from the system.
Expansion tank cap repair
Without paying due attention to such an insignificant, it would seem, element as a cover, the driver may face serious engine damage. Few people know, but the expansion tank cap controls the pressure in the cooling system. Special valves inserted into the cavity of the cover relieve excess pressure or release air in order to increase the volume of antifreeze required for circulation in the system.
The cover reliably seals the cooling system, and also serves to stabilize the internal pressure of antifreeze (antifreeze)
Repair of the tank cap includes three stages:
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Disassembly.
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Cleaning.
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Replacing elements.
At the same time, even a novice driver can complete all the stages.
How to disassemble the cover
Self-repair of the expansion tank cap is the simplest procedure, since the cap has a simple design and no special tools are needed to restore it. All you need is your hands and a thin flat-blade screwdriver. You need to act according to the following algorithm:
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Unscrew the cap from the tank.
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Pull out the product and clean it with a dry cloth from drops of coolant.
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A rubber seal is inserted into the cavity of the cover - you need to pry it with a screwdriver blade and pull it out.
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Then remove the spring, which lies under the rubber.
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Immediately under the spring you can see a small valve device - also pry it off with a screwdriver and pull it out. Next to the first is the second valve - it also needs to be removed.
This completes the disassembly of the expansion tank cap. All components are dismantled - you can start cleaning them.
Photo gallery: procedure for disassembling the cover
- Removing the cap from the neck of the expansion tank is usually not difficult - just turn the cap several times
- When disassembling the cover, it is necessary to carefully remove the rubber seal - the tightness of the cooling system will depend on its condition
- All elements are pulled out of the lid cavity - you need to make sure that each of the components is in working condition
How to clean the expansion tank cap
After the parts of the cover have been removed, you need to thoroughly rinse the cavity of the product itself. In practice, soapy water and cotton swabs are used for washing. The purpose of this procedure is to clean deposits of dust, dirt, coolant leaks from the cover cavity.
It is easiest to clean and rinse the cavity of the lid with cotton swabs, as they allow you to effectively remove all dirt deposits from the lid.
After all hard-to-reach places in the cover cavity are cleaned with a cotton swab and soapy water, you can install the parts in the reverse order. In this case, it is recommended to replace the spring or rubber seal if they have visible damage or deformation.
The principle of operation of the cap of the expansion tank
When the engine heats up, the coolant also heats up. At the same time, since the SOD is absolutely hermetic, excess pressure is created. All SOD begins to expand, and excess air accumulates at its highest point - the expansion tank. Further, under the influence of compressed air, the outlet valve of the expansion tank opens, and excess air escapes.
When the engine cools down, the process is reversed. The pressure in the system drops, and in order to avoid decompensation, that is, a decrease in the pressure level in the tank below atmospheric pressure, the inlet valve opens and sucks air into the system.
A common question on the Internet is how to check the expansion tank cap yourself.
Indeed, this cover is an important part for ensuring the performance of the entire machine. Why?! Imagine that the cap of the expansion tank is cracked or threaded
Accordingly, the coolant (antifreeze, antifreeze, distilled water) that is filled in the system begins to leak or evaporate. And after a while it becomes insufficient to maintain a normal, operating temperature of the engine. As a result, the engine
How to check the expansion tank cap? Let's consider this question in more detail. There are several types of covers, depending on the make and model of the machine - plastic, iron, and a combination of both of these materials. Accordingly, first unscrew the lid from the barrel and inspect it visually for scuffs, cracks, rust and wear. There is a spring in the middle of the cork niche. Check her condition. To do this, squeeze on both sides with your fingers.
If the resistance of the spring is not great and you squeezed it easily, it is out of order. The spring is necessary to hold the liquid at the moment of boiling. If it is weak, then the cover will simply be torn off and thus other spare parts under the hood, or even the hood itself, can be damaged.
The next stage of verification
, it is necessary to open the vacuum valve and make sure it is fully closed during lowering.Then the seat, which is located under the plug, should be tested for dust or dirt accumulations. If necessary, clean it with a damp cloth or sponge. In winter, after cleansing, you need to blow it out of the remaining water.
To carry out the next stage of the test, you will need a specialized tonometer to measure the pressure under the lid of the expansion tank. Screw the pump onto the plug and check the pressure according to the instructions.
Increase the pressure until the value on the tonometer stops. It should be remembered that the opening pressure of the valve must correspond to a value of (85-110) kilopascals, and when it is closed, 85 kilopascals. If your device shows a pressure significantly below 79 kilopascals, then the expansion tank cap should be changed.
With this device
possibly check for faults and the cooling system. The most obvious reason is: leak. To check, install a tonometer on the neck of the expansion tank. Next, create pressure up to 0.12 millipascal and check that the tonometer shows this value for 10 seconds. If the numbers differ, look for the leak accordingly. It is easy to detect by streaks on the details.
If, after carrying out this self-test, you find that the cover is not suitable
Treat the purchase of a new cork with special attention. Take the old one with you to the auto shop and, according to its marking, select the appropriate one.
After all, many plugs are different from each other, even there is a brand, and the model of the car is the same,
The attention of drivers who are accustomed to servicing their car on their own is usually riveted to the engine and chassis. Of course, these nodes are considered the main ones in the operation of the entire car.
However, equal attention should be paid even to such seemingly insignificant details as the cap on the expansion tank. What role does this element play in the cooling system? Most drivers do not even realize that the quality of engine cooling depends entirely on this cover!
