The size of an air tank refers to the volume of the tank, and is measured in liters or m3 (1m3 = 1000 liters). The air tanks on a compressor are used to store and supply air on a regular basis.

As mentioned in our previous articles, the air tank has no influence on the flow rate, although some users believe that the problem of insufficient air can be overcome by increasing the size of the air tank. This is completely false. If the air is insufficient in the plants, the first thing that should be checked is the capacity of the compressor.

#### Situations in which the size of the tank is important:

In addition to those mentioned above, there are other special cases in which a larger air tank would be required. For example, when using a machine that consumes air (pneumatic), or when the machine works once for a certain period and consumes large amounts of air. Let us try to explain this with an example:

The amount of air consumed is 1500 l/min in one second when operated once –**this is consumed air (ca)**.

When your machine works once, the time of consumption is 5 seconds – **this is consumption time (ct)**.

Machine requires a minimum pressure of 6 bar.

Calculation:

ca * ct= the total amount of air consumed in one work cycle

5 * 1500 = 7500 liters, the total amount of air consumed in the work cycle

We know that 7500 liters of air is consumed within 5 seconds, and so we need to choose the air tank accordingly.

This can be calculated using two different methods.

##### 1st Method – increasing the pressure.

Let’s assume we have a 1000-liter air tank, and the pressure is 8 bar. In this case, when our air tank is full, 8 * 1000 = 8000 liters of air will be stored.

It would appear that the 8000 liters of air stored in our air tank would meet the 7500 liters of air required by the machine, but since the machine’s minimum operating pressure is 6 bar:

(1000 liters (nominal volume of air tank) * 6 bar) = 6000 liters is our lower limit.

8000 – 6000 = 2000 liters of air in the tank, as the available amount. But 7500-2000 = 5500 liters, so more air is needed.

**Result: The air is insufficient.**

If we think we were going to use 15 bar pressure with the same air tank (1000lt)

15 * 1000 = 15000lt, which is the total amount of air stored in the air tank.

Lower limit = 6000 liters.

15000 – 6000 = 9000 liters, which is the amount of air available in the tank

7500 liters is the amount our machine needs, at a pressure of least 6 bar at any one time.

**9000 > 7500** – meaning that the available air quantity is greater than the amount of air needed by the machine.

9000 – 7500 = 1500 liters of surplus air, increasing the amount of air remaining after use.

6000 + 1500 = 7500 is the total amount of air in the tank after use.

7500/1000 = 7.5 bar total pressure remaining in the tank after use.

**Result: The air is sufficient.**

#### 2nd Method – Increasing the size of the air tanks

Considering a 5000-liter compressor air tank, when the compressor comes to 8 bar, 8 * 5000 = 40,000 liters, which is the total amount of air that may be stored.

Because of our air tank volume has increased, 6 * 5000 = 30,000 liters, and we have the lower limit at a pressure of 6 bar.

40000 – 30000 = 10000 liters of storage volume of air that can be used.

**10000 > 7500** – the available air quantity is greater than the amount of air needed by the machine.

10000 – 7500 = 2500 liters of surplus, increasing the amount of air after use.

30,000 + 2,500 = 32,500 liters, which is the total amount of air remaining in the tank after use.

32500/5000 = 6.5 bar, which is the pressure in the tank after use.

**Result: The air is sufficient.**

If you paid attention, you would have seen that no calculations were made related to the capacity of the compressor, as I assumed that the machine waited long and run the one time, and that the compressor fed only this machine. If this machine is run often, the capacity of the compressor will need to be increased.

Evaluation:

In the first method, a 1000-liter vessel must be resistant to high pressures. An air tank that is to be subjected to 15 bar is required to be tested and certified by authorized persons with water to at least 23 bar.

##### Advantages:

• Since the tank volume is small, there are advantages of space.

• Low cost.

##### Disadvantages

• The compressor providing the air must be designed to suit high-pressure compressors. In reciprocating compressors, high pressures can be reached in two steps, while in screw compressors, the recommended maximum pressure is 13 bar, and the speed should be reduced by acting on the belt-pulley system.

• Prices are high in comparison to a 1000-liter air tank to be subjected to 8 bar, as the sheet thickness of the tank is increased.

• The risk is greater.

The more the air is compressed, the higher the air pressure will be, and the greater the air pressure exiting the vessel. While this pressure can sometimes be an advantage, there are disadvantages too.

In the 2nd method, the pressure in a substantial volume 5000-liter tank is increased to 8 bar.

##### Advantages

• Any 8bar compressor can be used to fill the tank.

• There is no need for high pressures.

##### Disadvantages

• Volumetrically, it occupies a greater area.

• Transportation costs are high.

Note: the dimensions of a 1000-liter vertical air tank are approximately 200 cm high and 80 cm in diameter. In contrast, a 5000-liter air vessel is about 380 cm high by 130 cm diameter.

Different tanks to those given in the example can also be used, and using the same logic you can reach conclusions about the maximum pressure and capacity.

Text can be confusing, but I tried to explain as clearly as possible. 🙂