Help! Conversions of pressure!

[The MG Pony]

I'm totaly stuck on conversions of Inchs of Murcury vac to Micrones (Hg" vac to Microns)

M=Microns

The way the instructer showed us was M-(Hg'a-Hg'vac*25400)

and other such conversions, I just can't seem to make it work!

[Brian_UK]

Have a quick look here for some numbers to play with...

http://wiki.xtronics.com/index.php/Pressure_Conversion_Table

[The MG Pony]

Neat chart, the whole conversion thing is annoying me about this course too many numbers to memorize in just 1 week!

[Pooh]

Pony
have a look at this site lots of conversion bits

http://www.engineeringtoolbox.com/

Ian

[thermo prince]

Steady up there MG Pony ,,,, take it in steps. Dont get hung up on the instructor's formula but instead try to reason where the relationship "inch to mm originates. The it makes more sense .... so

1 "inch measure = 25.4mm, as on measure tape .... we all agree

also 1mm = 1000 microns or 1 micron =1/1000 mm ( if we were to divide 1mm into a thousand equal portions)

therefore, 1 inch " anything, expressed as microns will be
25.4 x 1000 = 25,400micron.

So for example, on evacuation we are trying to get the " last inch" from 29" to 30" Hg as you can see on your compound(blue) gauge - that can be expressed as 25,400micron.

One of the reasons we do this is you cannot readily 'see' 1 inch on compund gauge but we can sure see when expanded on micron scale of , say a Hastings Hi Vacc Analogue or digital vacc gauge.

Typically using 2 stage vacc pump we are then trying to pull down to 500 micron and hold it there. That's getting close but not exactly to the 30" gauge or 0 abs - that's plenty good already for HVACR. Only NASA or some labs need to go lower than ,say < / =50 micron.

Hope this helps - try engineeringtoolbox also as Pooh suggested but there are many good sites.

regards and good luck ... take it step by step

[The MG Pony]

Steady up there MG Pony ,,,, take it in steps. Dont get hung up on the instructor's formula but instead try to reason where the relationship "inch to mm originates. The it makes more sense .... so

1 "inch measure = 25.4mm, as on measure tape .... we all agree

also 1mm = 1000 microns or 1 micron =1/1000 mm ( if we were to divide 1mm into a thousand equal portions)

therefore, 1 inch " anything, expressed as microns will be
25.4 x 1000 = 25,400micron.

So for example, on evacuation we are trying to get the " last inch" from 29" to 30" Hg as you can see on your compound(blue) gauge - that can be expressed as 25,400micron.

One of the reasons we do this is you cannot readily 'see' 1 inch on compund gauge but we can sure see when expanded on micron scale of , say a Hastings Hi Vacc Analogue or digital vacc gauge.

Typically using 2 stage vacc pump we are then trying to pull down to 500 micron and hold it there. That's getting close but not exactly to the 30" gauge or 0 abs - that's plenty good already for HVACR. Only NASA or some labs need to go lower than ,say < / =50 micron.

Hope this helps - try engineeringtoolbox also as Pooh suggested but there are many good sites.

regards and good luck ... take it step by step

THANKs with that finaly got it to work!, some times it comes all down to how it is explained and worded!!!

(Murcury absalute subrate murcury vacuume times 25.4)* 1000 gave the right answer ((29.92-29.90)*25.4)*1000= 508 microns

[Brian_UK]

Yep, and then some fool will ask you "How many Torr is that then?" ;)

[The MG Pony]

Ah Tor to micron is just a decimal! Micronsis exact same as millitorr! :)

[Peter_1]

And now you understand it, you can sue some free software http://www.katmarsoftware.com/uconeer.htm

[The MG Pony]

I have a conversion program, a couple to be exact but we must learn to do it manualy I tend to remember formulas better then charts or tables and hes showing us to use a chart, so the chalange is how to make a formula out of the chart.