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Feb 2013
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Originally Posted by larnot
We're mixing our Rankines with our Kelvins here.
larnot caught it - my apologies. I said Kelvin, but the correct term is Rankine. The formula I posted is in Fahrenheit, and one degree F equals one degree Ra. Zero degrees F equals 460 degrees Ra, thus why we add 460. The formula is correct, I just called it the wrong thing.

One degree C equals one Kelvin.

Originally Posted by garyed
So 90 F converts to 305.37 kelvin etc. but the answer ends up about the same for the pressures. I don't know which is more accurate but I would think converting to celsius is more precise than just adding 460.
Using (460 and Fahrenheit degrees) or (273 and Celsius degrees) would be equally accurate, however if you convert F to C the accuracy depends on how accurately you convert between the two. If you round up or down then accuracy will suffer accordingly. If you really want to be picky, you would use 459.67 or 273.15 with the appropriate (F or C) scale.

2. Originally Posted by DDC_Dan
...............
Using (460 and Fahrenheit degrees) or (273 and Celsius degrees) would be equally accurate, however if you convert F to C the accuracy depends on how accurately you convert between the two. If you round up or down then accuracy will suffer accordingly. If you really want to be picky, you would use 459.67 or 273.15 with the appropriate (F or C) scale.
My calculator uses C + 273.15 but I tried 459.67 & they both work out exactly the same up to ten decimal points so the accuracy is the same so that answers my question, thanks.

3. what is this used for

4. Originally Posted by garyed
It just shows how much the temperature changes the pressure. Lets say you were leak testing a system & put in 350 psi of nitro over night. If it was 95* out when you pressurized it & it was 65* when you got back to check in the morning then it should be 330 psi. if there were no leaks. The pressure change is pretty minimal & I've never used a calculator for it but I figured I write one today since the question was asked.
This is what it's used for, pressure testing for leaks with varying ambient temps.

5. thank you

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