PST E7-series tanks and Variable volume

[netdiver]

I'm getting ready to invest in some HP steel tanks and have been evaluating the various manufacturers and options.

I'm interested in the PST cylinders for the variable volume to accomodate different service pressures. I'm not very experienced, but I know not all filler stations provide fills up to 3442 PSI that HP steel can accomodate. This means I can get more usable air from a 3000 PSI fill on the E7s than I can on those without.

Their web site is pretty pathetic though. I cannot find any tank specs like weight, length, diameter or description of this magical variable volume system.

Is this a bladder system? Does anyone know of any resources on the net with more specific information about their tanks?

 

[Scubar]

I have attached the link to the spec sheet. http://www.pstscuba.com/specsheet.pdf

There is no bladder in these tanks its just Boyles Law: P1V1=P2V2

The words "Variable Volume" seems to be nothing more than a sales line. This will hold true for any cylinder. More pressure more volume less pressure less volume.

 

[Mark Vlahos]

I'm getting ready to invest in some HP steel tanks and have been evaluating the various manufacturers and options.

I'm interested in the PST cylinders for the variable volume to accomodate different service pressures. I'm not very experienced, but I know not all filler stations provide fills up to 3442 PSI that HP steel can accomodate. This means I can get more usable air from a 3000 PSI fill on the E7s than I can on those without.

Their web site is pretty pathetic though. I cannot find any tank specs like weight, length, diameter or description of this magical variable volume system.

Is this a bladder system? Does anyone know of any resources on the net with more specific information about their tanks?

In this thread I have included a chart that shows the volume of lots of different cylinders at differing pressures. The brand of the cylinder is not important since the relationships of pressure and volume are derived from mathematical formulas that only care about the internal volume of the cylinder and the pressure you inflate it to.

I hope this helps.

Mark Vlahos

 

[netdiver]

Got it. It seems the diving industry uses the term "volume" in a very liberal way and I was interpreting it very literally. The volume of a cylinder does not increase with pressure except in small amounts due to flexing of the walls under pressure. PST used it in very deceptive and effective way!

BTW..Great chart and very useful. Thanks for posting it.

 

[ChrisA]

I'm getting ready to invest in some HP steel tanks and have been evaluating the various manufacturers and options.

I'm interested in the PST cylinders for the variable volume to accomodate different service pressures. I'm not very experienced, but I know not all filler stations provide fills up to 3442 PSI that HP steel can accomodate. This means I can get more usable air from a 3000 PSI fill on the E7s than I can on those without.

Their web site is pretty pathetic though. I cannot find any tank specs like weight, length, diameter or description of this magical variable volume system.

Is this a bladder system? Does anyone know of any resources on the net with more specific information about their tanks?

PST has been having some problems. Last I heard they went broke but were bought out. Don't know if they are currently making tanks but Worthingtom makes a full line of tanks with the exact same specs as PST. Worthington calles theirs anr "x7". Faber also now makes these tanks but they are painted white not hot dipped. Some prefer the white pait others like the hot dipp galvanized.

As for "magical variable volume system" There is NO magic. It just works out that if to fill the tank to 3/4 of it's rated pressure you have a 3/4 full tank. "Duh". Now a more complex example: Lets say you fill a tank to 3000/3440 of it's rated pressue your 100 cu ft tank then holds (3000/3440) X 100 = 87.2 cu ft. See, no magic.

The e7-100 is a great tank and 87 cu ft is still plenty of ait for most dives, The tanks is thr same physical size is a standrad AL80 but 2 inches shorter. It is about 1 pound negative at 500 PSI. If you dave an AL80 now you can take about 5 pounds off you belt and you get abut 10% more air even with a 3000psi fill.

 

[CompuDude]

There was a report herejust a few days ago that PST is getting back in it's feet and expects to be back in production by August or September, if memory serves. Just FYI.

But yes, if you're concerned for any reason, the Worthington tanks have nearly identical specs.

I don't care for the Faber tanks, personally. Paint chips, Galv. does not. Plus they're a LOT heavier than the PST/Worthingtons, on land and in the water. More weight off the belt, but a lot tougher to lug around, too.