[Solved] Understanding Low-Pressure Household Gas Systems: Gauges, Values & Measurements

Hello

Recently, I had an argument with my brother-in-law, a gas fitter, about the pressure in the home gas system. He told me that to measure them you need a very expensive pressure gauge, which is calibrated to 0.8 atm and the pressure of such an installation in the block is about 0.2 atm. I told him that he must have made a mistake because if that was the case, the gas under such pressure would never come out of the nozzle - after all, we breathe air with a pressure of about 1 atm. I didn't have access to a computer at the time, but today I checked that he was right. According to wikipedia, gas in low-pressure household systems has a pressure of 10 kPa. On the reducer of an 11 kg gas cylinder, the reduced pressure is 3.6 kPa (read from the plate), so what is it about?

Or maybe all these pressure values are relative, differential values and in fact if the pressure gauge shows 0.2 bar, the absolute pressure is 1.2 bar? Does this only apply to the gas industry or, for example, the pressure gauge at the gas station, which I use to check the tire pressure, also shows the value relative to atmospheric pressure?

Regards

Vic

Apologize to your brother-in-law and don't make a fool of yourself

I apologized to him a long time ago but this means that manometers show relative pressure where the reference point (zero on the scale) is atmospheric pressure?

Yes, and those that measure vacuum are vacuum gauges.

There are simply two ways to represent pressure and vacuum. One is absolute and the other relative to external pressure. One is suitable for some applications, the other for others. The pressure gauge can be such and such, the vacuum gauge always measures relative to the atmosphere and hence the readings are negative. But in addition to vacuum gauges, there are other vacuum gauges that measure absolute pressure. Absolute measurement is more applicable to vacuum, pressure is probably most often quoted relative to the atmosphere. So a pressure of 0.2 atm is, as the name "pressure" suggests, 0.2 atm above atmospheric pressure. The pressure in a bicycle tube, in a gas cylinder, etc. is measured in a similar way. After all, when you go to the station to pump the wheels, the indicator on the unconnected hose shows 0 and not 1

The pressure in the home installation should be 20 mba, which gives 0.02 atm