300-500 psi intermediate from my scuba tank?

[spoolin01]

I use an old scuba tank and Dacor primary for pressurized air around the garage, and for bringing my inflatable boat up to pressure. A simple 150 psi adjustable secondary regulator permits tuning the supply to the task. A need for higher pressure has come up, and I'm wondering what the options are for accessing 300-500 psi from my old tank?

I've not looked into standard gas bottle regulators, I just assumed they wouldn't be compatible with the tank threads, and then I'd have to be able to fill them... don't know about service pressure either. Are such things available or adaptable? I do have one ultra-LP tank with 1/2" pipe threads, but I'd probably rather have something suitable for 3/4" standard format.

Is it possible to adapt a scuba primary to safely produce 300 psi? 500 psi? I don't have insight into which parts might not handle the increased load, so I thought I'd ask. I'd guess the ports would be OK, but I don't want to blow one apart at the seams, or even risk it! Permanent modification of the primary would be fine, just not catastrophic, is all.

Flow wouldn't be an issue - I live with the Dacor for 0-100 psi now - but can a scuba primary be modified for higher flow, or is some sort of conventional regulator needed?

ETA: if there's a standard industrial adjustable regulator with adequate service rating, >3000 psi, I guess I could couple that to the HP port, not sure what flow could be achieved that way.

 

[captain]

What you want to do can't be readily done with a scuba regulator. You would need this.

https://www.breathingair.com/products/regulator-high-pressure-6000-psi

And this to connect it to a tank.

https://www.breathingair.com/products/yoke-scuba

 

[DA Aquamaster]

I would not subject a swivel turret to that kind of pressure due to concerns over whether the retainer nut would handle the extra pressure, but a reg with the ports in a solid first stage body would probably work fine. 3/8" LP port threads do after all work fine in old first stage HP ports at 3000 psi, so 500 is a cake walk.

Hose selection is an issue however. Most are rated for a service pressure of about 240 psi with perhaps a 1.5 safety factor. A few are made for a service pressure of about 400 psi with a similar safety factor. The latter would probably work for you but a better option is to have a hydraulic shop make something to your specifications.

In terms of making the reg generate the pressure, you just need to replace the spring with one that is suitably stiff. The math is pretty straight forward but you want to be careful not to over compress the spring as that can lead to failure. And not all designs are going to be suitable in terms of the space available to accomodate a suitably larger/stiffer spring.

 

[spoolin01]

What you want to do can't be readily done with a scuba regulator. You would need this.

https://www.breathingair.com/products/regulator-high-pressure-6000-psi

And this to connect it to a tank.

https://www.breathingair.com/products/yoke-scuba

Now why didn't I think of that! I'm pretty sure I've got a spare yoke and release, and that solves the fill and bottle compatibility concerns. The ticket on that regulator is way up there. I'll do some checking but that probably puts this project out of the running.

I would not subject a swivel turret to that kind of pressure due to concerns over whether the retainer nut would handle the extra pressure, but a reg with the ports in a solid first stage body would probably work fine. 3/8" LP port threads do after all work fine in old first stage HP ports at 3000 psi, so 500 is a cake walk.

Hose selection is an issue however. Most are rated for a service pressure of about 240 psi with perhaps a 1.5 safety factor. A few are made for a service pressure of about 400 psi with a similar safety factor. The latter would probably work for you but a better option is to have a hydraulic shop make something to your specifications.

In terms of making the reg generate the pressure, you just need to replace the spring with one that is suitably stiff. The math is pretty straight forward but you want to be careful not to over compress the spring as that can lead to failure. And not all designs are going to be suitable in terms of the space available to accomodate a suitably larger/stiffer spring.

Guess I'll dust off the physics book for a review of spring constants. I wasn't sure if parts of the body casing were designed to only anticipate normal intermediate pressure - though that strikes me as something of a risky design - thanks for the tip about the swivel primaries.

I'm mindful of the pressure rating issue, I'd have to confirm each component's suitability. I may have seen a 400psi hose in my collection of spares. I could live with that.

This got started because I decided to rehab a couple of pneumatic spearguns that I've had for a few years that have never held air. One I don't have a pump for, and thought I'd make an adapter to work with the standard speargun pumps that I do have, and then thought while I was at it that I'd set up to fill the guns from a bottle instead. That appeals to a sense of precision for the process. If suitable parts can be had reasonably, I may still go that route, since at least you didn't say it was too crazy!

 

[captain]

Be mindful that at those pressures it will have to be a piston type regulator, a diaphragm regulator's diaphragm will not handle much over 200 psi.

 

[herman]

Would the orings also need to be upgraded to a higher durometer? Just mulling it over and that seems like something that would be necessary as well. I wouild think it would be a good idea to uprated any 70s to 90s.

 

[spoolin01]

While the idea of reworking a scuba reg sounds intriguing, the opportunity for rude surprises or worse makes me inclined towards a professionally engineered reducing regulator. It seems there are plenty available in the $40-$100 range that should be mateable to a yoke. Some can handle 3000 psi or more, some would have to be kept to a partial bottle.

 

[spoolin01]

Would the orings also need to be upgraded to a higher durometer? Just mulling it over and that seems like something that would be necessary as well. I wouild think it would be a good idea to uprated any 70s to 90s.

I was looking into pneumatic speargun servicing recently and THINK I saw that the o-rings used in those are 70 durometer. Those guns can be used as high as 400 psi or more. I suppose there's more to it on the component tolerance side, but 70 works there at least. Wish I had better command of reg design - which o-rings only see IP, aside from the LP ports?

 

[captain]

While the idea of reworking a scuba reg sounds intriguing, the opportunity for rude surprises or worse makes me inclined towards a professionally engineered reducing regulator. It seems there are plenty available in the $40-$100 range that should be mateable to a yoke. Some can handle 3000 psi or more, some would have to be kept to a partial bottle.

Regulators are rated for the input pressure, not the output pressure. Most of the less expensive regulators are low output pressure diaphragm regulators such as used on welding cylinders and commercial gas cylinders and usually have output pressures of 150 psi or less. High output pressure piston regulators even used usually cost $$$

 

[spoolin01]

I was cruising eBay last night and indeed most regulators were rated for fairly low input and even lower output but I found a handful that could handle 1000-6000 psi input and provide output up to 700 psi or so and with NPT ports, that were still less than $100, some new even. It's clear that most are made for 300 psi or less output and not much higher input. There were quite a number of the large dual-guage higher pressure rated gas bottle-top regulators, like you see on industrial N2, CO2, Argon, and such tanks, but they are pricey as well as specially configured for attachment, and as you say likely not set up for 500 psi output, though I didn't check them for that.