Tank Question..

[Superlyte27]

Guys:

Did I read somewhere that there was an issue getting PST tanks to pass hydro? Was this HP or LP tanks? Anyone know the scoop?

[Walter Pickel]

Never had an issue with mine

[Sludge]

Was this HP or LP tanks?

Neither. It's the E-Series.

The E-Series is simply a LP cylinder with different numbers stamped on it. But the problem is, they are still hydro tested to 5/3 working pressure. So instead of being tested at 4000psi they're tested at 5700psi, where they're much more likely to fail.

If I have some of these numbers wrong, someone correct me. But that's the gist of it.

[JS1scuba]

Rus,

The E series is not the same cylinder as the LP cylinder.

PST made three series of cylinders prior to 2005.

The LP Series was a service pressure of 2400 psi plus a 10% over fill to get the rated volume. These would get a 5/3rds working pressure hydro test.

LP-45, LP-80, LP-95, LP-104, LP-120

The MP Series was a servide pressure of 3300 psi plus a 10% overfill to get the rated volume. This would get a 5/3rd working pressure hydro test.

MP-72

Then the HP Series (also known as Genesis series) was introduced in 1988 and was the first exemption series. This had a 3500 psi working pressure and no overfil. It would get a hydro at 3 / halfs working pressure or 5250 psi. These used the 7/8 14 small neck thread and were required to have a 300 bar din outlet valve.

HP-65, HP-80, HP-100, HP-120

All of the above worked well for many years. However ...... around 2002 Thermo introduced the Convertible Pro Valve and wanted to get big sales out of it. Thermo was heavily involved with CGA advisory panels, NFPA advisory panels etc and carefully looked at the Valve requirements for scuba. If a cylinder had a working pressure of less than 3450 psi it could use a "K" or "Yoke" Style valve. But if it was 3500 psi or more it was required to have a 300 bar din valve. .......... Since Thermo wanted to sell a lot of valves it was important to get tanks that were rated at less than 3500 psi ....... welcome 3442.

BTW this applied to PST, Faber, Heiser etc. (Faber sold the most) Worthington was not in the scuba cylinder market then.

For the HP series this would just mean changing the neck size from the smaller 7/8 14 thread to the standard 3/4 thread and slightly changing the height. That made the E series for PST for the 7.25" cylinders. For the larger 8" diameter cylinders they would need to make complete new engineering drawings, get new DOT testing etc. so that this whole new series of cylinders would meet DOT requirements. (Faber too)

Now the E series is both the 7.25" and the 8"

In 8" you have

E8-119 (similar in size to LP 95)
E8-130 (similar in size to LP104)
E8-149 (similar in size to LP 121)

Here is a tank chart from our website that pretty much has all the cylinders on it. http://www.tdl.divebiz.net/pub/tanks.html


The reason scuba cylinders fail hydro from time to time is because they have lost their elasticity. The biggest way a cylinder will lose its elasticity is to constantly over-fill the cylinder beyond it's working pressure AND leave it full. The "sustained load" is what wrecks the cylinder. I'm not a metalurgist so i dont know the exacty reason why it loses its elasticity but its like bungee-- stretch it long enough and keep it under tension and sooner or later it does not come back.

.... High Pressure steel cylinders tend to fail more often than Low Pressure industrial cylinders. (we have some we have tested as old as 1915) I've seen PST and Worthington's fail on first hydro. And fail badly (in the test range) when I ask the owners about overfilling and HOW long the cylinders sit between use - invariably they are filled fat and then sit for a month or more before use. Or they are filled fat daily and just generally abused.

Scuba cylinders are like car tires. They need to be replaced every once in a while. I know it sucks when a cylinder fails hydro but it is just part of the game. This year alone I had 5 of my own cylinders fail hydro. I think they served me well over the years. 3 were aluminum, 2 were steel.

This may have been a longer reply than you were looking for but .... what the heck. It's good info.


Cheers
JDS

[Sludge]

Jo,

I was told, off the record by someone at PST, that the LP and HP used different steel alloys, and that the 3442 E-Series was the same alloy they had been using on the LPs, so the E-Series was for all intents a HP with a 3/4 neck.

It was off the record so I can give no citation.

[JS1scuba]

Jo,

I was told, off the record by someone at PST, that the LP and HP used different steel alloys, and that the 3442 E-Series was the same alloy they had been using on the LPs, so the E-Series was for all intents a HP with a 3/4 neck.

It was off the record so I can give no citation.

It most probably was the same alloy but the wall thickness is different. It may not be a lot thicker (like the MP cylinders) but it is different. I've had a chance to view a lot of the Faber specs, engineering drawings etc (I was big distributor for a few years) and each and every cylinder goes through a lot to get that spec approved for manufacturing. Remember these are big bombs if not made correctly.

Cheers
JDS

[cavemark]

There is a unique procedure for hydrotesting some PST tanks the if not followed will result in a higher failure rate.

[KarsticGator]

Jo,

I was told, off the record by someone at PST, that the LP and HP used different steel alloys, and that the 3442 E-Series was the same alloy they had been using on the LPs, so the E-Series was for all intents a HP with a 3/4 neck.

It was off the record so I can give no citation.

I thought PST closed up shop??

[Sludge]

the LP and HP used different steel alloys, and that the 3442 E-Series was the same alloy they had been using on the LPs, so the E-Series was for all intents a HP with a 3/4 neck.

I must have been smoking crack when I typed this, as it makes no sense. If the E-Series is in fact the same alloy as the LP, it is not related to the HP.

I don't think we'll get a definitive answer since PST closed up shop (thanks, unions), and I don't want to dispute what Joel said (after all, he's been at this a lot longer than me), but what I alluded to makes the most sense. If you stop testing a cylinder at 4000psi and begin testing it at 5200psi, you're going to get a higher failure rate.

I don't have any firsthand knowledge of a single hydro failure of a 2400 PST cylinder, even ones that have been pumped to 3600 for 35 years. But I know some people whose logic says, "If we can take 2400 tanks to 3600, let's take 3442 tanks to 4400." I believe this is overfilling them, and when you test them at 5200psi some are going to fail.

[JS1scuba]

I don't have any firsthand knowledge of a single hydro failure of a 2400 PST cylinder, even ones that have been pumped to 3600 for 35 years. But I know some people whose logic says, "If we can take 2400 tanks to 3600, let's take 3442 tanks to 4400." I believe this is overfilling them, and when you test them at 5200psi some are going to fail.

Around 2004 when PST and Faber went to making 3442 psi exempt series cylinders they both went out and made an 80 cuft cylinder rated at 2640 psi to compete with the aluminum 80. This was a thin wall cylinder that was light and had all the similarities to an alum tank but not the weight or size. It fell under the E series exemption getting a 3/halfs hydro as well ........ the manufacturer made it really clear that this cylinder should not be overfilled. We had some of them. When you filled them they would get very hot very fast, they would float when empty. BUT they were inexpensive as an aluminum cylinder.

I think a few hundred were made by Faber and not much more by PST. I have not seen them in years. I think I still have one or two on my rental rack.

Cheers
JDS