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Originally Posted by Swampdude
Ok, with that info, it still boils down to the desired pressure. For instance, you could put a fan pointing out a hole and as soon as you turn it on, voila - negative pressure in the room. Not much, but less than ambient. So if your next question is whats a good pressure before the trailer crushes like a beer can? It sounded like you may be contemplating letting this pump run regularly to maintain this pressure over time? Also depending on the contents you may want to remove oxygen, and not necessarily draw a negative pressure. Because this isn't going to have the effect of a ziploc bag since the volume of space will not reduce hence displacing atmosphere. You may be better suited to "fill" the room with nitrogen, a great purging resource that displaces oxygen.
Besides all that, lets say you wanted to get the trailer to -20psi in 1 minute, and you already gave the volume of 40'x8'x8.5'.
2 options from here are:
1. you oversize the pump and use a pressure regulator to regulate with a +/- of acceptable range - which would have a big motor and little pump
2. you size the pump to run constant -20psi - which would have a big pump little motor
I assume you'd want option 1 - for efficiency?
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If it can suck 680cubic ft, I believe we will be ok. Yes we want this pressure to be consistent, weather it means on and off toggling or consistent pressure. Oxygen will always remain. Great suggestion on the nitrogen,
We have already come up with other ways of this as well. I will leave that for another thread. From all the calls placed to different manufactures of vacuum motors seems that the largest tubing usable, would be ¾’in.
I will throw these 2 options to the guys in the morning and reply back a.s.a.p. I guess its as you said, we are going to have to determine a PSI to aim at to achieve and look at the results it provides to find out weather its adequate.
Yes efficiency would be most important to me, however the others may think differently. We all have different aspects of this project and tend to think in different directions, at times.