@Fadedawg
Ran a negative pressure test and it held -30" hg for about 3-4 hours, let it sit overnight and about 24 hours later was around -28.5" hg. Is this sufficient?
Yes! Nature hates a vacuum, and atoms of air like N2, will leak where the larger C-3 H-8 propane or C-4 H-10 butane molecules won't. One hour without measurable loss is our acceptance standard.
Also was wondering if one TRS-21 pump would be efficient or if it's not even worth the money for the meantime. If it's not much of a difference to running passive I'd much rather just save up for a Haskel than end up with dual TRS-21's.
When running fixed displacement pumps like the TRS-21, under certain conditions, two pumps are about twice as fast as one, but once pressures go negative, that is no longer the case.
Ignoring volumetric efficiency for a moment (in Heaven), when a fixed volume pump piston makes one stroke, it pushes the volume of that cylinder out. The actual volume of gas present in that cylinder with only zero gauge or atmospheric pressure on the intake side of the pump, is different than if the intake is under vacuum or positive pressure.
If the intake is under one atmosphere of pressure (14.7psi), also known as zero gauge, and volumetric efficiency is 100%, the piston will shove out one volume of the cylinder's swept area (.7854D2 X stroke).
One atmosphere is 29.92" Hg, or 760,000 microns. If the intake is under 50% as much pressure, or about 14.96"Hg/380,000 microns, one stroke of the piston will produce 50% as much output, because only half as many molecules of gas are there, just spread further apart.
If the intake is under pressure, each multiple of 14.7 psi (one atmosphere in Heaven) will increase the actual volume of the cylinder by one volume. If the intake pressure is 45 psi, 45/14.7 psi = 3.06X, so one stroke of the piston will discharge 1 + 3.06 volumes per stroke.
There is also the issue of surface area boiling, which is limited, so exceeding its ability to vaporize is a waste of horsepower.
Sooooo, the short version is that the gas is recovered fast until you reach negative pressure and negative pressure is where you spend much of your recovery time. Two pumps are an advantage on the front end, but less so on the back end.
In commercial production, time is money, but if you have more time than money, starting with one certainly works.
P.S. if anyone could link a source for 20-24" 3/8 sae SS PTFE hoses, that would be clutch.
