Tank Valve Service Pressure

[AquanutAlex]

Hi all, I recently purchased a used set of HP100s in backmount doubles configuration. They include the valves + manifold pictured below. Of note, the valves each have a sticker on them saying "3000 psi service pressure". So my question is: What is truly meant by "service pressure", and is it safe to use these valves with HP tanks filled to the 3442 psi capacity (plus a little more for hot fills)? Of note, each valve has a 5000 psi burst disc on it. Thanks in advance for the info!

 

[Divin'Papaw]

X7-100 (HP100) tanks should have a manifold/valves with 5250 burst discs. The manifold on your doubles currently is for 3000 PSI (AL80) tanks. Those valves use a 5000 psi burst disc. You should at least replace the burst disc with 5250s. That is also a good time to service the valves. Other than that, I believe the manifold itself is identical and should be fine.

 

[Nick_Radov]

Are those 200 (5 turn) or 300 (7 turn) bar female DIN connectors? It's hard to tell from the picture. Most isolation manifolds are 300 bar now and should be fine but there are still some old 200 bar manifolds floating around.

(Some older 3500 psi HP steel cylinders used oddball 7/8"-14 UNF thread size which required a different valve but I don't think that's what you have here.)

 

[rjack321]

Are those 200 (5 turn) or 300 (7 turn) bar female DIN connectors? It's hard to tell from the picture. Most isolation manifolds are 300 bar now and should be fine but there are still some old 200 bar manifolds floating around.

I think you mean the reverse, 300 bar are definitely out of favor around here in Puget Sound. More turns to install the reg or whips, more opportunity to get out of round, 300 bar adds basically no value over 200 bar.

 

[TrimixToo]

Are those 200 (5 turn) or 300 (7 turn) bar female DIN connectors? It's hard to tell from the picture. Most isolation manifolds are 300 bar now and should be fine but there are still some old 200 bar manifolds floating around.

(Some older 3500 psi HP steel cylinders used oddball 7/8"-14 UNF thread size which required a different valve but I don't think that's what you have here.)

They sure look like 300's, but as you say it's hard to tell from the pics. I opened one in a new tab and blew it up 250%. At that level of magnification it's hard to count the threads...but it sure looks closer to 7 than 5. OTOH all my tanks are LP so the one or two 300's I have are mostly a pain in the neck. However, 200's are still available from a number of manufacturers: Tanks - Valves - Valves - Manifolds - Northeast Scuba Supply Store

It's quite right, though, that a 300 bar manifold should not be marked with a 3000psi service pressure limit.

 

[Tracy]

Are those 200 (5 turn) or 300 (7 turn) bar female DIN connectors? It's hard to tell from the picture. Most isolation manifolds are 300 bar now and should be fine but there are still some old 200 bar manifolds floating around.

That is a 300 bar manifold pictured and you have it backwards. 300 bar was a big thing in the 90s and early 2000s but have finally almost all but gone away.

To the OP, the 5k burst discs will be fine. They should be 5250 on HP tanks but yours fall within the margin of error that will work just fine.
Whenever you get the valves serviced next, that would be a good time to have the burst discs replaced with the proper ones.

 

[rjack321]

It's quite right, though, that a 300 bar manifold should not be marked with a 3000psi service pressure limit.

The 300 bar fitting has nothing to do with the service pressure of the tanks, you could put that manifold on LP tanks too

 

[OMyMyOHellYes]

OK - let's talk about the question that the OP actually asked - **usually** the only difference in valve ratings is the PRD/burst disk. ("300 BAR" vs "200 BAR" length of threaded throat acknowledged - but also note that 200 BAR valves are perfectly serviceable on 3,442# bottles. You don't change over to the 300 BAR valves until you get to 3,500# or higher bottles.)

Normally, the PRD/burst disks are rated to 5/3 of the bottle's service pressure. A 3,000 rated valve will have a 5,000 PRD/burst disk. The PRD/burst disks on 3,442 bottles will typically be 5,250# rated - that is lower than the 5/3 rule of thumb, but that's what the valve and tank engineers came up with.

Note that the delta in tank capacity is 442#; the delta in PRD rating is 250#.

Being conservative (using a slightly lower rated disk) on the PRD hurts nothing other than it may be ever so slightly more prone to popping, depending on how far past the SP the tank is filled and maybe the number of fill cycles. Me, personally, I would not be so much concerned ab0ut the 250# under rating as I would be the age of the PRDs themselves. They need to be replaced every 5 years, usually at the same time that the bottle is hydroed. Most local shops (IME) that pimp out hydro services will roll their eyes if you ask and do not do this unless specifically requested. They will also do the same when I've asked about regular valve rebuilds which the valve manufacturers recommend at that interval too... In any case, as I don't ever know when/if it has been changed when I buy used bottles; those get changed out with no further consideration (usually I'll be rebuilding the valve or replacing the valve (most of my used buys have K valves and they get converted to Pro valves.)

The PRDs are cheap (<$10) and easy to change - you do have to properly torque them so you'll need a wrench with the right rating if you don't already gots one.

PRD Safety Assembly (Burst Disk Kit)

One thing to be aware of - if the valves have the older multi-part washer/disk parts rather than a single assembly (which is what you commonly see today), the copper burst disk can be a little problematic to get out: I have had those rip through and I've ruined a couple valves by scratching the valve surface where the PRD assembly seats. I have re-thunked my position on removing those with a pick and will going forward use a low pressure (100#?) air supply and blowing them out using the dip tube once I've removed the rest of the parts. This will however necessitate removing the valve from the bottle.

 

[TrimixToo]

The 300 bar fitting has nothing to do with the service pressure of the tanks, you could put that manifold on LP tanks too

I'm aware. I have one LP twinset with a 300 bar manifold, as it happens. I was talking about the pressure rating of the manifold itself.