Advice on used HP100s, I think 7/8" neck

[topher10]

Short Story
I would appreciate any advice on these tanks, particularly the valves. My research suggests PST HP100 with the 7/8” neck/valves (3500), legal only for DIN regs and only for air, and therefore cannot be used for either nitrox or with yoke regulators. My regs are yoke and I dive nitrox.

Long Story
I found these two tanks for sale at an excellent price. The owner says they are HP100s which he used for years, but that he is no longer diving and they have been sitting full for several years now. The VIP stickers are for December 2012 and March 2013. I asked for the tank stamp for both of them, and was sent pictures but can only make out one of the two stamps:

DOT-E9791-3500 TP5250 8-88 USA 713757 P.
Above and below the 8-88 are re-stamped for 7-93, 12-99, 12-12, which I assume are hydro dates.

It seems that these are likely PST Steels with the 7/8” neck. Also, notice the funky angle to the valve. I planned to buy new “Pro” valves with the DIN/Yoke insert, but they do not fit this 7/8 neck. In fact, the only valves that fit this type of neck are XS Scuba valves which are not compatible with the yoke adapter, not labeled for nitrox compatibility, and a bit more expensive.

The owner says he used a Yoke adapter, which can be seen in one of the pics. But this looks like it might be an old DIN-yoke fill adapter and not recommended for diving.

Therefore, if I want these tanks I would need to swap my regs to DIN, but still would not be able to legally use nitrox. I am sure there are workarounds, but my conclusion is that these tanks are enough of a problem that I should pass, despite the excellent price.

Thanks for any input, suggestions or corrections.

 

[happy-diver]

Fight the rot

3/4 inch only

 

[swimlikethefish]

You can most definitely use them with nitrox. Have them O2 cleaned. I would not purchase them without having a look inside / them having a new hydro done. Maybe use that in your negotiating.

As far as your regs. They need to be din. Those are 300bar din valves and you can not use a yoke adapter. Those valves are perfectly suitable for use with nitrox or air. If you want to band these tanks and make doubles your are limited to a new thermo 7/8 Manifold for $$$$, or some good luck. In which case you might find a 7/8 older Manifold here in the classifieds, they show up every few months.

 

[topher10]

You can most definitely use them with nitrox. Have them O2 cleaned. I would not purchase them without having a look inside / them having a new hydro done. Maybe use that in your negotiating.

Am I correct here:
1. If I had a DIN reg these tanks/valves could be used for nitrox with O2 cleaning.

2. If I want to install new valves, the only valves available are the XS Scuba valves which are DIN only and not nitrox compatible: XSS Valve, 300 Bar DIN outlet, 7/8 UNF inlet threads | Dive Gear Express®

Those two points perhaps beg the question of how often one should change valves, and if its good practice to replace the valves on a 32-year-old tank.

Thank you for input.

 

[swimlikethefish]

1. Correct (only 02 cleaned if filled with nitrox using the partial pressure blending method. Otherwise if filled with banked nitrox they wouldn't specifically need to be O2 cleaned)

2. Why buy new valves at all? Those valves are suitable for single tank diving. Just have them serviced (cleaned and new orings.) if you wanted to Manifold them for doubles is where you would get into spending a few hundred unless you could find a used Manifold somewhere.

3. The most significant thing you are overlooking is: hydro. I would be hesitant to buy a 30 yr old tank that has been sitting (presumably since 2012) whether it was filled or not. I would only buy on the condition it passes hydro.

 

[swimlikethefish]

To add:

2. Ignore the air only label. Those valves can be used for nitrox if cleaned with the appropriate orings. <-- referring to the xs scuba valves you looked at that are new.

 

[happy-diver]

I wonder why DGX, the biggest scuba supplier around, does not stock 7/8 UNF manifolds

and then only lists a 7/8 UNF single valve as a specialty valve
at 300 bar which does not accept yoke adapters nor the regs


Perhaps it's because of their rare quality of almost catering to the obsolete

 

[swimlikethefish]

For education: this has been said before, I am saying it again.

A 300 bar din valve is 7 threads deep. A 230 bar din valve is 5 threads deep. All yoke adapters are 5 threads deep. You can not use a thread in yoke adapter on any 300 bar din valves. For the curious...

200 BAR DIN vs 300 BAR DIN

 

[bletso]

What is really nice about the PST E9791 is that thay are 100 cf and when full weigh only a little over a pound more than an AL80 full. PLUS, you can take off 4 #'s from your weight belt. I have 5 of them. All nitrox service. Most regs can be adapted to a DIN fitting, which is a better connector anyway. (IMO)

 

[topher10]

I appreciate all the advice. I am still unsure what to do and leaning towards passing.

The issue is that even if I get the tanks cheap, I will have to travel to get them, pay for Hydro/VIS, risk them failing or try to negotiate with the owner to hydro them first, pay for valve service or potentially new valves, and convert both of my regs to DIN. When all of these additional costs are added they are not as cheap as advertised, and at the end of the day I still have 32 year old tanks.

If I already had DIN regs I would probably go for it. I know this is a minor issue (I should have gone DIN from the start), but its enough of a barrier to make me hesitate.