Pressure, Flow, Volume, Temperature

Questions & AnswersCategory: GeneralPressure, Flow, Volume, Temperature
ThivinRaj asked 2 years ago

Hello sir What is the difference & relation between Pressure, Flow, Volume, Temperature and its effects?  

1 Answers
Cas Staff answered 2 years ago

I always say, pressure is ‘how strong’, volume is ‘how much’ and flow or capacity is ‘how fast’ or ‘how often’.
Compare your compressed air system to a water pump (the air compressor) that pumps water into a water tower (the air receiver).

The water level in the tower is the pressure.

The amount of water (liters per minute) the pump pumps into the tower is the capacity.
The size of the water tower is the volume.

If we have multiple compressors, we can add up their capacities. So two smaller compressors equal one big compressor.

But we can’t add up the pressure. Two 7 bar compressors are still 7 bar.

Also, that 7 bar is the maximum output pressure, it can output less.

To go back to the water tower example. When the pump (the compressor) starts up, the water level is 0 (pressure is 0). When the pump is switched on, the water level rises (pressure rises). The pump can pump up to a maximum water level (air pressure).

If we add another pump (compressor), we can still only reach the same water level in the water tower (maximum air pressure), but since we are pumping with two pumps, we will fill up the water tower faster.

Temperature has little effect on this in our everyday operations. You could calculate the difference by using “Gay-Lussac’s law”: P1/T1 = P2/T2.

You will need to use absolute temperatures here (Kelvin), which is Celsius + 273.
So if you have a container (constant volume) with 7 bar compressed air of 20 degrees. And you heat it up to 30 degrees, the pressure will increase. ( 7 / (20+273) ) + (30 + 273) = 7.23 bar.

Here’s a Wikipedia page with the main gas laws that you might find interesting:

In our daily operations of compressed air systems, you don’t need to concern yourself with this.

The only thing to remember about temperature is that your compressor will run more efficient, uses less electricity, when you ‘feed’ it cold air instead of warm air.

Here’s a picture from my latest course on compressed air. All this is explained in detail:

Hope everything is clear now.

All the best,