Is low pressure dangerous?

To be honest, none of us attach any serious importance to this device. Well, the cover – what to take from it – it is only suitable so that the coolant does not splash out! Percent think 90 percent of motorists. Although this is fundamentally not true, if this “plug” on the expansion tank of your car fails, at least the coolant will constantly spill out, and as a maximum it can provoke a number of unpleasant breakdowns. So you need to know – how the basic principles of its device work. As you guessed, today I will talk about it …


For a start, a small definition

Tank cover – is a locking element, which has in its structure two valves, high and low pressure. This element protects the cooling system (CO) of the car from damage, and also normalizes the work.

In fact, to call a lid or a cork – the tongue does not turn, I would say so – this is a pressure adjustment sensor, only with a cork on top!

Tank lid task

As you know, when the engine is warming up, the coolant heats up as well – it expands. Accordingly, this creates an increased pressure that is greater than atmospheric, it is natural. It should be noted that slightly increased pressure in the CO, this is not bad, and not good, the engine by and large – all the same! The main thing that it was enough for the functioning of the system. It should also be sealed.

If you want – it can be compared with a boiler for heating a house. The boiler is an engine, the pipes are pipes, the expansion tank is there and there.

The more heated antifreeze or antifreeze, the more pressure occurs in the system. It should be noted – that many old units operate at temperatures of 90 – 95 degrees. But modern engines have great performance, so it’s not uncommon to work at 100 – 110 degrees Celsius, for example, my AVEO is a high-temperature motor, its normal figure is about 115 degrees. As you understand, these are average values, but at the peaks they can reach even greater values ​​of 120-125. Coolant at such temperatures can increase by 20 sometimes even by 25% – here you have an overpressure.

Is low pressure dangerous?

In order not to break the tubes, radiators, pipes and the expansion tank itself was invented a special valve, which is located in the lid.

Normal pressure in various systems, on heated engines should be in the range from 1.1 to 1.5 (bar) atmospheres. More is already dangerous.

Just as the pressure rises much higher, the cooling system can be damaged, in simple terms, it will simply break all of your hoses or, worse, radiators.

Here then the expansion tank cap comes into play, it “pits” excessive pressure, bringing it back to normal, say 1.1 atmospheres. In this way, all your connections and hoses will remain intact.

Low pressure is also dangerous!

Just imagine – you went on business in the winter, and then put the car on the joke (to stay overnight), the antifreeze will begin to cool and decrease in size, that is, settle down. And the pressure will also begin to fall (after all, the valve has thrown off the excess and closed), so that a decrease in pressure will begin to create a weak vacuum. Hoses and pipes will be compressed inside – which is also not good.

Again, the expansion tank lid begins to work, it also has a reduced pressure valve, that is, if a vacuum starts to be created, then the system opens and replenishes with air. Hoses extend – to normal level.

Thus, the expansion tank cover – works in one (high pressure) side and in the other (low). This is a very smart and very necessary element of the system, despite all the simplicity.

Very often, first of all, it protects radiators from damage (after all, they are expensive on foreign cars).

The device, the principle of the tank cover

As I indicated above, the task of the lid is to keep the pressure to a certain limit. It becomes clear that it should sweat to the tank and not give pressure to bleed, up to a certain limit – 1.1 – 1.5 atmospheres.

The lid itself holds almost nothing, it is only needed to press the high – low pressure valve, which is immersed in the neck of the expansion tank.

As a rule, there are one or two sealing gaskets on the valve body, which act as original glands. In many foreign cars, the valve is one, it is also the inlet and outlet, that is, it can release and build up pressure.

It is worth noting in many domestic VAZ, the lid is arranged differently, there are physically two valves here, one you guessed it works only to relieve pressure, the other to force it (normalize) to normal.

These valves are called:

Is low pressure dangerous?

  • Safety – against high performance
  • Vacuum – from low values

But as long as the pressure in the system is normal and both are closed – they do not work, this is the norm! However, a cover often breaks down and it is difficult for a simple motorist to determine (and it is very difficult for a beginner), although this entails quite expensive breakdowns. Now a few words about the signs, this is not good.

Symptoms of a failure of a cover of a broad tank

Often the high-pressure valve fails, it just starts to throw off the antifreeze at a normal rate, or it doesn’t throw it off at all.

  • When you throw off the normal pressure (when the engine is warm), there is a splash of antifreeze or antifreeze and, accordingly, its decrease. Often can drop steam from under the hood, because the liquid enters the red-hot exhaust manifold. Moreover, the engine temperature is not in the red zone, that is, it is working – it means 90% of the cover.
  • If a vacuum valve fails, completely different signs will appear. So often there are air traffic jams in the system – this leads to the following, the engine overheats, and cold air flows from the stove.

To be honest, there can be a lot of reasons, for example, another one of the signs is when the tube breaks or breaks the clamps. YES and the tank itself can burst – it says that the high-pressure valve does not throw off the “surplus” and it begins to exceed 1.5 atmospheres, by the way, the radiators themselves can also be damaged, let me remind them of the two main and stoves (in the cabin).

So if you started to snotty, connecting clamps or other connections, often knocks out the hoses – change the cover.

How to check the work yourself?

To be honest, this is a bit problematic, the valve – the lid needs to be either pressurized or lowered.

Is low pressure dangerous?

However, first you need to inspect it visually, if you notice cracks, scuffs, tearing of gaskets, or other mechanical damage – then this is most likely a cover. Also, the internal elements of the valve may become useless from time to time, some manufacturers recommend changing these plugs every two to three years, then there will be no problems.

Now a few simple ways to determine the fault:

  • Start the engine, warm it up, then gently start to unscrew the cover, if “pshik” happens, then it keeps its “atmosphere”, most likely working.
  • We look at thick hoses, if they are severely deformed, as if squeezed, then the vacuum valve does not work – the replacement cover.
  • There is another way, but not always it can be used. We unscrew the cover from the tank, squeeze one of the thick hoses strongly, then without releasing the hose we tighten the cover – if they take the original forms, it means our cork is working. If not, change. The only drawback is that on many modern foreign cars it is quite difficult to do this.

Of course, at many stations there are special pressure pumps, to which they screw caps with a tank and inject — 1.5 atmospheres; after this critical indicator intersects, the valve should open, if this does not happen, it means that it is faulty.

In conclusion, I would like to say that on many foreign cars the lid breaks when unscrewing, the valve itself remains inside the tank, and doesn’t come out from there. This suggests that the vacuum that was created inside does not allow her to go out! A replacement is needed, not because it is broken, but because the valve is “dead”.

This is how the article turned out, for those who are lazy, watch the video version.

At this end, I think it was interesting, read our AUTO BLOG.

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