Is there a temperature vs boiler pressure table?

#1: Post by **Kristi** » February 7th, 2007, 9:12 pm

is there a temperature vs boiler pressure table?

Can someone please point me to it?
Thanks

#2: Post by HB » February 7th, 2007, 9:24 pm

#3: Post by **jesawdy** » February 7th, 2007, 9:42 pm

Here's Eric's table adjusted for altitude

IIRC you have to add the barometric pressure to the gauge pressure to use the steam table link that Dan referenced above.

February 7th, 2007, 10:25 pm

Thanks.

Why, on the table, does 250F => 2.05bar and on the graph 250F = 1.05bar?

(I am at sea level)

#5: Post by **gabriel** » February 7th, 2007, 10:56 pm

does a table exist to show the relation between the boiler temp/pressure to the brew-head temp on HX machines ?

#6: Post by **jesawdy** » February 7th, 2007, 11:15 pm

Kristi wrote:Why, on the table, does 250F => 2.05bar and on the graph 250F = 1.05bar?

Eric's graph indicates "gauge pressure". When you use the steam tables, you have to add "atmospheric pressure" (Patm) to "gauge pressure" (Pg) to get "absolute pressure" or P.

Adding 1 bar at sea level is about right.

1 bar = 0.987 atmosphere = 29.53 inches of mercury

To be precise about it, add the atmospheric pressure (as reported by the weather conditions in your area) to your gauge pressure reading to determine absolute pressure, P.

#7: Post by **jesawdy** » February 7th, 2007, 11:19 pm

gabriel wrote:does a table exist to show the relation between the boiler temp/pressure to the brew-head temp on HX machines ?

Ah, there's the rub.... this will vary machine to machine.

Depending on what machine you have, someone here may have a good idea of the approximate temp difference, but only with testing could you determine that, and you still have the variable of how much one flushes.

February 7th, 2007, 11:22 pm

jesawdy wrote:Eric's graph indicates "gauge pressure". When you use the steam tables, you have to add "atmospheric pressure" to "gauge pressure" to get "absolute pressure" or P.

Adding 1 bar at sea level is about right.

1 bar = 0.987 atmosphere = 29.53 inches of mercury

To be precise about it, add the atmospheric pressure (as reported by the weather conditions in your area) to your gauge pressure reading to determine absolute pressure, P.

THANKS!

So if I am measuring a temp of roughly 250F on the side of the boiler under insulation, and the boiler gauge says 1.5, something is screwy?

#9: Post by **jesawdy** » February 7th, 2007, 11:32 pm

Kristi wrote:So if I am measuring a temp of roughly 250F on the side of the boiler under insulation, and the boiler gauge says 1.5, something is screwy?

Maybe, maybe not. How accurate is your temperature reading? Meter? Thermocouple? Calibrated? And finally would the outside boiler temp equal the internal temp? (Of course it should be close)

1 bar (Patm) + 1.5 bar (Pg) = 2.5 bar which corresponds to 261F on the saturated steam tables.

February 8th, 2007, 12:18 am

aaaaah

hmmmmm

250F - 1.05Pgauge
261F - 1.48Pgauge

so a difference of .5 boiler Pgauge bar only yields 11F
But it seems more like raising .25Pg gave me a rise of 15F....

Accuracy - K tc on a Fuji Pid being used for temp read only. Fine wire K - bare wires twisted on end.

tc is under scotch double sided tape pad stuff so it acts as a bit of an insulator, with insulation over that. tc is attached to bottom of boiler.

tc checks out at 32.6 and 212.5

What started this was I am questioning the accuracy of the boiler gauge and wanted to """calibrate""" it.

The other prob is that my Mater seems to want to have a .3 or .4 deadband and probably needs replacing, but since it works I'll just leave it (I took it off and checked the microswitch, but all looks good. But it's 4 years old.)

Put it back together and running
1.20bar ON 240F
1.45Bar OFF goes up to 245.5

But I have no idea of the accuracy of the gauge.