What happened to PST

[oxyhacker]

I don't think there is any question but that 3AA tanks are safer in an absolute sense than the SP tanks. But for highly stressed and regulated products like tanks, safety can be defined not by how long they will perform, but by how likely it is that they will give ample warning so they can reliably be weeded out long before failing catastrophically. I suspect they are pretty equal in that regard - the 3AA may have a potential life of 30 hydros and the SP only 5, but as long as they get those hydros, the odds against them bursting while in service and hurting someone is probably pretty much the same.

Ron, that is a very good point you make about the 10% overfill and relative 3AA and SP test pressures. The 5/3s and 3/2s just aren't as different as they seem. There was a proposal some years back to eliminate the "+" by re-rating eligible tanks like the 3AAs to 2/3s of the current test test pressure. This would have made the fill pressure for the 2400 psi LP steels (currently 2640 with the "+") ... 2666 psi!

One could make the arguement that SP or E cylinders are less "safe". SP/E cylinders are hydro'd to 3/2 while 3AL and 3AA cylinders are hydo'd to 5/3. 66% is more than 50%!

Just a point for discussion.

 

[Leadking]

2400 3AA hydro = 2400x1.66=4000
2400 as a SP hydro=2400x1.5=3600

the 3AA cylinder has an additional 10% pressure

10% is 10%

 

[oxyhacker]

Take two 3300 psi steel tanks. One is a SP tank and the other is a 3000 psi 3AA tank qualified for the "+" (these are not actual tanks but just examples).

The 3300 SP tank would have a test pressure of 3/2rds of 3300, or 4950 psi

The 3300 "+" 3AA would have a test pressure of 5/3rds of 3000, or 5000 psi.

Test pressure for a 3AA is based on the stamped service pressure, not the fill pressure. A 3AA tank that is qualified for the "+" (as all good ones should be) is actually functioning as a 3300 psi tank, but is hydroed as a 3000 psi one, so the real-life ratio of its test pressure to the pressure it will actually be used at is much closer to 3/2s than to 5/3s.

2400 3AA hydro = 2400x1.66=4000
2400 as a SP hydro=2400x1.5=3600

the 3AA cylinder has an additional 10% pressure

10% is 10%

 

[Leadking]

Pressed Steel went out of business...twice...basically beaten down by the urban renewal folks in Milwaukee. Nothing wrong with their cylinders, they were/are outstanding performers. Be cautious buying them used, however - the most recent iteration of PST sold cylinders under a DOT exemption that will be expiring in a bit. After that it will at least be an aggravation to get them hydro tested and it may not be possible at all. There have been several threads, search is your friend...

Give me a break! PST went out of business for two reasons.

1. It invested heavily into cng technology for the auto industry and it did not pan out
2. Their notorious reputation for non-delivery

I met with one of the Darling family to discuss distributing their cylinders at OWU in 2002. They could would NEVER give me a plan to convince me that I could deliver cylinders to my customers on a timely basis. I went to Worthington and worked to set them up in the scuba business. Walked out with a handshake deal worth over $3 million.

By the way, if you ever drove by their old plant in West Allis, you would understand why the City re-developed the facility. They had not put a nickel into maintaining the facilities in 50 years. Boarded up windows, abandoned buildings and on and on.

 

[WD8CDH]

Ron, that is a very good point you make about the 10% overfill and relative 3AA and SP test pressures. The 5/3s and 3/2s just aren't as different as they seem. There was a proposal some years back to eliminate the "+" by re-rating eligible tanks like the 3AAs to 2/3s of the current test test pressure. This would have made the fill pressure for the 2400 psi LP steels (currently 2640 with the "+") ... 2666 psi!

For a similar reason, there have been some LP "SP" tanks. Some were made with stronger steel but thinner walls to give the same pressure rating, but some were made EXACTLY the same as 3AA tanks but the SP allowed them to be stamped at the equivalent 10% overfill as the service pressure (the 3AA2400 +10% tank was stamped as a 2650psi/no overfill SP tank) strictly to eliminate the "plus" part of the hydro testing and eliminate the possibility of losing that "plus".

 

[WD8CDH]

I don't think there is any question but that 3AA tanks are safer in an absolute sense than the SP tanks. But for highly stressed and regulated products like tanks, safety can be defined not by how long they will perform, but by how likely it is that they will give ample warning so they can reliably be weeded out long before failing catastrophically. I suspect they are pretty equal in that regard - the 3AA may have a potential life of 30 hydros and the SP only 5, but as long as they get those hydros, the odds against them bursting while in service and hurting someone is probably pretty much the same.

I would say that without corrosion, they would handle equal numbers of hydros and with corrosion, the ratio of hydros would be approximately equal to the ratio of wall thickness. That would be assuming that the 3AA tanks were usually filled to their +10% fill pressure.