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I want to know the difference between barg and bara. how can I convert them?

BarG - (Gauge Pressure) Pressure reading relative to current atmospheric pressure.
BarA - (Absolute Pressure) Pressure reading relative to absolute vacuum.

i.e. If a tank has a positive pressure of 350 mBar and the atmospheric pressure of the day is 1006 mBar then the readings would be.

BarG = 350 mBarG
BarA = 1356 mBarA

There is no conversion from BarG to BarA as atmospheric pressure changes from day to day but the range of change is about 50 mBar. If you add 1000 mBar to a BarG reading then it will convert to BarA but will be +/- 50 mBar.

Steve Linehan

Bar(Gage) is relative to local atmospheric pressure, while Bar(Absolute) is relative to absolute pressure. How to convert them depends on the local atmospheric pressure.

MB
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bar a = bar g + 1

Bara (Absolute pressure) is a pressure mode where the reference pressure is absolute zero, i.e. not taking into account atmospheric pressure (which is approx 1 bar), where as Barg (gauge pressure)is referenced above atmoshperic pressure.
Thus the difference between an absolute pressure value and a gauge pressure value is the variable value of atmospheric pressure:

Absolute pressure = gauge pressure + atmospheric pressure.

Hope this helps.

Barg = Bara + your local atmospheric pressure in Bar's

Dennis

Hi sir,

I think you are wrong.
bara = barg+ atm pr.

Is it correct?

barg means bar-gauge (gage)
bara means bar-absolute (including atmospheric pressure)
bara = barg + atmospheric pressure (Atm),
if 1 Atm = 1 bar,
bara = barg + 1.
Is it answer the question?

best regards,
FX Bambang

Some of you seem quite confused. The first few posts got it right, went down hill from there.

Bar Absolute is not related to atmospheric pressure at all, it's related to absolute vacuum, e.g. if you have a pressure of 1.2 Bar Absolute it doesn't matter what the atmospheric pressure does, it's still 1.2 Bar Absolute.

Your weather report calls out the atmospheric pressure in Bar Absolute so you know the pressure of the atmosphere related to an absolute vacuum.
The pressure of the atmosphere is always zero Bar Gauge at sea level or 20,000 feet, wet or dry.
An altimeter (traditional) is a pressure gauge that measures the pressure related to absolute vacuum. The reading is effected by the weather. An early way to measure elevation was to boil water and measure the temperature it boils at.

If you see a pressure in Bar it's Gauge, you don't need to add the "G". A pressure gauge reads Gauge pressure. An absolute pressure transmitter is like a DP cell with the low pressure side under a perfect vacuum. We use them on evaporators to keep the conditions constant no matter what the weather does.

Hope I haven't added to the confusion!

"I'm sure this thread is going to be a long one".

Regards,

Roy

I am a little confused. If I have a vessel that operates at atmospheric pressure, then what should I see on a pressure gauge???

= 0 barg??? or ~ 0.01 barg???
Also, I don't quite understand, when people refer to bar, they meant to say bara???

Cheme,
If they say bar, kPa, psi, or just about any other pressure unit you should assume it's gauge, If they mean absolute they should say so, adding a g is redundant and annoying.
Just remember a pressure gauge reads g pressure.

There are some units that are based on absolute e.g. Torr

On your vessel you will see 0 bar, 0 kPa, 0 psi 0"WC etc.

Hope this helps
Roy

bar a = barg +1
:-)