meter math

[DM546]

i have a 4" chamber at 19" long iv done the math using the formulas and the burnt latke calculaters and have gotten differnt outcomes when i did the formulas myself it said i would need 143 psi using a 1/2"x5" meter chamber using the calculater and putting 90psi for the supply tank pressure it tells me i need a 5" meter pipe, how can this be?

[starman]

The 143 psi calculation is closer to being correct for that size meter pipe and chamber. For a chamber of that size, you should pick a meter perhaps 2 or 3 times that volume so you can load it with a much lower psi. You can only get 90-120 psi out of a propane tank under warm conditions, and it's much lower in cool and cold conditions, so finding a meter volume that can be loaded with say 50-60 psi would be much more desirable. You can use a basic regulator on your propane tank to limit output to the desired level.

Also beware the advertised size of pipe isn't the actual size of the pipe. Note for instance 3/8" galvanized is actually 1/2" ID. use the actual measured size of the ID to perform calculations.

[DM546]

thanks for the help i kind of realised that i would need a bigger meter after seeing the psi outcome,

but why did the burnt latke calc say i needed 5" even when i supplied the tank pressure of 90psi

[starman]

It's probably assuming that 1/2" pipe is actually larger than that, 5/8" or so. That would lower the psi requirement because of larger volume than you might think on the surface.

To reiterate, always measure the actual ID of the meter pipe you are using and use that number in your calculations.