Okay, for this design, the volume of propane needed to fire at 1x is:
[(620ci/95.98 )*100-620]
26ci. (actually 25.9691ci, but we wouldn't want SB15 to be offended
).
Now, your meter will likely be full of air on the first shot, so on the first shot you would need to fill it to:
{[(26+9.4)/9.4]*14.7}
55psia or 40.7psig.
On the second shot, if the meter is full of propane, you would need:
[(26/9.4)*14.7]
41psia or 26psig.
Remember, this is all for 1x.
At 2x, you would need:
{[(620*2)/95.98]*100-620}
52ci of propane, requiring a meter pressure of 81psig if the meter was full of air or combustion products to start with, or 67psig if the meter was purged with propane beforehand.
Note that these numbers don't take into account the miniscule effect of the air or combustion products that might be in the meter if it wasn't purged.
Judging by these numbers, you couldn't usually exceed 3x without having to dump the meter twice, which complicates things even further. Ever thought of using a chamber pressure meter instead?
Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.
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