This was originally posted on the Lego page, and closed because it's not actually about Lego itself. I thought I'd give them a chance first, in case someone had done this already and had some application-specific knowledge. Then my next stop is here, since you guys are probably more familiar with the gear that I'm looking for.

I have this, that I want to power with a HPA, paintball, auxiliary SCUBA, or whatever-someone-decides-to-call-it tank:

enter image description here

I think a 6.1cm diameter, 0.22L or 0.35L tank will fit nicely in place of the 0.5L plastic water bottle. I can redesign things and move some structure around if I have to, but the overall size is pretty well fixed.

The air inlet is a sports inflator needle pushed into the black hose in the front, with a bicycle pump currently attached to it. The maximum pressure there is about 35psi (~2.3bar).
I can use a longer hose there if needed too, but that's about as short as it can be. The straight section with a slight kink is the inflator needle.

So, is there a compact way to regulate the HPA tank from 3000psi (200bar) down to 30psi (2bar) with a schrader-valve type connection at the end?

enter image description here

I see that a fair number of HPA tanks (but not all) come with a factory-attached pre-regulator, that can apparently be adjusted by taking it apart and changing the spring. But it seems like a stretch to me, to take something that is designed for 3000psi in / 800psi out, and get it all the way down to 30psi out instead. Maybe it's possible, and if so, that's great! But it seems like a bit much to me.

It seems more likely to me, to just barely get into the range that a shop air regulator can handle, and use that for the final delivery as well as a complete shutoff. But there are still adapters to be found, and perhaps some creative folding to make it all fit in the available space.

I also found this, which says it takes 4000psi in and is fully adjustable from 4000psi out to 0psi out. It looks a bit cumbersome at first glance, compared to the space that it would go in, but no real size reference except for the gauges. Also, with such a wide range of adjustment, it might be difficult to have it "barely on" and stable at my required 30psi. Not to mention a rube-goldberg chain of adapters, probably on both the inlet and the outlet sides of it.

Is there an elegant way to get the required 100x drop in pressure, with decent regulation (there's a throttle valve after the final regulator), in the space shown, and with the right connector at the end? (imitation schrader valve)

  • $\begingroup$ :/ Unfortunately I can't see how it would be about chemistry, either. $\endgroup$ – Mithoron Jun 12 '20 at 22:17
  • $\begingroup$ @Mithoron Do you know a site that would take it? $\endgroup$ – AaronD Jun 12 '20 at 22:32
  • $\begingroup$ I'm not sure, perhaps engineering.stackexchange.com ? You've account there so should know better... Mod can migrate it if there's consensus, $\endgroup$ – Mithoron Jun 12 '20 at 22:42
  • $\begingroup$ @Mithoron Oh yeah. I'd forgotten about that one. I'll have to poke around there again and see if it fits. Thanks for the reminder! $\endgroup$ – AaronD Jun 12 '20 at 22:50
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    $\begingroup$ I’m voting to close this question because it belongs to engineering and was already cross-posted. $\endgroup$ – Mithoron Jun 13 '20 at 13:04

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