What is the Vacuum Pressure value?

[buytree]

Googled it and I was getting the vacuum pressure is 29.921 in of HG (Gage). Corresponding conversion for the other units are zero, from here

http://www.engineeringtoolbox.com/va...ter-d_460.html

Can anyone please tel whats the vacuum pressure in psia and psig?
Any comment will be most helpful. Thanks.

 

[zdas04]

"Googled" what????????????? What the heck do you mean by "vacuum valve" in the title? I'm assuming that you're a student and that this thread will go away, so I'm not going to put much work into it.

Gauge pressure is always measured from local atmospheric pressure. Are you on the coast? In the mountains? The reference changes with elevation.

If you're wanting to convert a specific pressure use Uconeer that was written by a long-term active contributor to eng-tips.com and is clearly the best unit conversion tool I've ever come across.

According to Uconeer, 29.921 inHg is -14.696 psig (convention is that inHg is positive from zero towards increasing vacuum, psig is positive from zero toward increasing pressure). So if you're in Denver, CO that reading is impossible. At sea level it is just possible.

psia=psig+local atmospheric pressure (so if local atmospheric pressure is 14.7 psia, 29.921 inHg would be 0.004 psia)

David

 

[hydtools]

29.921 in Hg is nearly perfect vacuum
psia = 0
psig = psia - atmos pressure = 0 - 14.7 = -14.7

Ted

 

[zdas04]

hydtools,
Did you read my post? 29.921 inHg is zero psia at exactly one elevation. In Death Valley it is nearly 0.1 psia. In Denver it is impossible.

David

 

[hydtools]

zdas04
Sure. And accepted local atmosphere in Denver is 12.2psia; and absolute vacuum is still 0 psia.

What do I feed this goat? I seem to have yours.

Ted

 

[zdas04]

Yep, pressure does not go lower than 0 psia. So if atmospheric pressure in Denver is 12.2 psia, then 0 psia is -12.2 psig or 24.8395 inHG. There is nothing magical about 29.921 inHg, it is just the pressure that corresponds to one of the values used for "standard pressure". It makes me crazy when people think that every time there is nothing in a container the pressure is 29.921 inHg.

David