Tanks

Hi folks, Looking to buy two steel tanks. Can someone explain the difference between low and hi pressure tanks? Pros and cons of each, Thanks to all

Sure, hp tanks tend to be either smaller than lp or more gas. They cram more gas into the tank, technical huh? Benefits are smaller size or more gas for same size. Drawback, can effect first stages due to higher pressures (although in 10 years of owning steels I've never had a problem). Sometimes harder to find fill stations for hp. But a short fill on an hp is sometimes more than an lp. Checkout divegearexpress as they have a good breakdown of charactersitics.


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A lot of people push lp tanks because they overfill them (normal fill pressure is 2640 and they fill to 3200-3500) I bought lp tanks for this reason. When traveling with them though I have trouble getting these kinds of fills because no one knows me and it is a violation of the dot rules. I am looking to move to large capacity hp tanks.

To to combat short fills drop the tanks off ahead of time. Then go back after they have had time to cool and check the pressure. If they aren't full get them to top them off. I haven't ran into a shop that can't fill an hp all the way yet.

One issue with HP tanks is that they are normally made under a special permit that needs to be renewed periodically. PST and Worthington no longer make scuba tanks and there is always a possibility that the permit will not be renewed which means a hassle in the US and possibly unusable tanks in Canada.

Thanks! Just what I needed to know, love this forum

Assuming you believe them Worthington stated that they planned to keep the permits up do date indefinitely so as not to destroy their credibility in the other things they still make.
As far as PST goes I would look up which ones need the round out before hydro test (just HP I think) and just avoid those unless you get a killer deal. My local hydro tester actually told me the roundout test doesn't follow DOT inspection procedures so he won't do it. He is the only tester in the area. Most hydro testers consider scuba tanks to be just a small part of their work and I got the impression the idiosyncrasies of the scuba industry requirements annoyed them.

I originally planned to get a steel HP100 or two as they seemed to be the best way to go (new HP vs new LP that is) and I dive singles right now. Then a pair of OMS/Faber LP85 doubles turned up cheap on craigslist with the bands and doubles manifold on them and they even came with the original single tank valves which I switched back onto them.

This was ideal for me because I got a matched pair of tanks to use as singles for far cheaper than what even one new tank would cost. I will eventually band them back together when I get a back plate and wing for doubles so its a big bonus to have all the hardware.
LP tanks aren't quite as in demand as HP tanks so the prices used tend to be lower.

Another advantage specifically for me is the pressure difference with LP's on equipment. It's much easier on gear, but its nothing your average person will ever notice. However if you are like me and rebuild gear yourself and wait until you notice the IP going for a walk or something before you go for a rebuild then the lower pressure is REALLY nice to have as it makes a difference in the long run on the HP seat.

With used LP tanks you have to really watch out for tanks with a history of overfills ("cave fills") as they cut the life of the tank short. I was able to verify that my tanks had never been overfilled and they both passed the +rating test by a wide margin of the REE #'s stamped on them. I got a sheet from the hydrotester with all that data and ideally any tank you buy should have its last hydro test data sheet.

If you buy new there is a certain site with sherwood HP100's that are a few years old but still new and being sold at a super discount for hydro test reasons. That was my plan for new tanks. The LP85's were a suddenly from left field craigslist thing.

Get the 3442psi tanks. Overfilling the LP tanks is great and all till you get a shop that wont do it, then you're up the creek without a paddle.

Roughly lp104s equal hp130s. lp95s = hp119s, etc.

Overfilling LP tanks decreasing the lifespan of tanks is a myth. I've got a set of 104s that are from the 80s (maybe early 90s) and they're fine, they even come away with the "+" rating. Same with wear on regulators. The regs that live on my al80s go just as long between needing a service as the ones that live on my steels that are filled to 3600psi.

Anyone can apply for the Special Permit renewal, not just the manufacturer. If push came to shove and PST or someone else didn't renew, I would do it. I have way too many of those tanks to just let it go.

The OP might be needing this info. Yolk regulators and valves are only rated for 3500 psi. If pressures are more then that, you must go DIN. Just another reason cavers use DIN.


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DogDiver:

The OP might be needing this info. Yolk regulators and valves are only rated for 3500 psi. If pressures are more then that, you must go DIN. Just another reason cavers use DIN. Sent from my iPhone using Tapatalk

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You can run yoke on HP tanks. It's about as much of a big deal as a cave fill.