Good price for double steel 100s

[spectrum]

The exemption is the special permit that the 3500 and 3442 PSI cyinders are manufactured under. It was acquired by Pressed Steel Tank (PST) and requires revision on 5 year intervals. I don't have the date handy but it's up for renewal soon (spring 2011?). There are a number of avenues for renewal and with PST on the ropes it may well be done by a personal application to the DOT that renews the permit for all. It's highly unlikely that there will be a problem since they have been safe cylinders and there are a lot of them out there. Renewal does not require any testing or reengineering, just an absence of probems.

As to this set the 3500 PST tells us these are the small neck cylinders DA mentioned. I have 4 of them and they are nice. They are not excessively negative. The catch can be servicing through the small opening. If they are in good shape it's a non issue. It's not an issue at this time since he will be getting them recommissioned. It also means that this may be the 3rd re-hydro if these have been in continuous service. The excepmption cyinders ahve not been quite are consistent at passing as the LP product but at this point it's a sellers risk. If tested correctly a problem is unlikely.

These cylinders are for DIN use only except for a few rogue valves floating around. If you're diving DIN all is good.

Setting aside the age of these you can benchmark against an X100 which generally sells for about $350. With bands and manifoilds a new comparable set starts to look like real money. Those cylinders by themselves can fetch $150 each with a fesh hydro and VIP. Put together as a doubles set $450 is a price that should let everyone sleep well.

Pete

 

[manni-yunk]

what would be considered excessively negative?

 

[DA Aquamaster]

An X7-100 is about 2.5 pounds negative when empty with valve and that is in the roughly "normal" range (-1 to -3 pounds) for buoyancy for an empty steel tank. Anything more than 4-5 pounds negative when empty starts to become increasingly problematic.

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The standard for chrome moly steel tanks is called "3AA" and tanks made to that engineering standard ared stamped "3AA". for the record the approved standard for aluminum tanks is "3AL" and for carbon steel it is "3A". Tanks with those designations meet common engineering standards that do not require any renewal process.

In the past there were several aluminum special permit and exempt cylinder classifications that were incorporated into the 3AL standard when it was adopted. These tanks should have been stamped with "3AL" at their next requalification but some of them got missed and still show up from time to time unstamped. And a couple of tanks that would have qualified for the "3AL" status were not recognized as the manufacturer let the permits expire and those tanks can no longer be legally requalified - but a few seem to keep getting missed by RINs that seem to ignore the expired permits.

On the other end of the spectrum there are "Exempt" and "Special Permit" tanks. These are tanks that are made under an exemption or special permit that requires renewal on a periodic basis and if the exemption or special permit is not renewed, the tanks can no longer be requalified for further service when their next hydro test is due.

3A, 3AA and 3AL tanks are normally hydrotested at 5/3rds their service pressure while Exempt and Special Permit tanks are normally hydro tested at 3/2 their service pressure and that reflects differences in the engineering stnadards and safety margins. In genral 3A, 3AA and 3AL tanks are over engineered to a very conservative standard which is why they are relatively heavy when compared to a similar volumed exempt or special permit tank.

The heavier weight is not all bad as 2400 psi 3AA steel tanks have a very good record of service when overfilled to 3600 psi service pressures - a testimony to the generous over engineering associted with the 3AA standard. However it did not scale up well to 3500 psi tanks as said tanks when made to the 3AA requirements tended to be very heavy and very negatively bouyant. For example, the Faber 3AA 3180 psi tank is nearly 6 pounds heavier and 6 pounds more negatively buoyant than the almost identically dimensioned 3442 psi PST E7-100.

The difference and lighter weight with E and SP tanks is often due to a combination of thinner walls using stronger or differently heat treated steel alloys.

 

[manni-yunk]

An X7-100 is about 2.5 pounds negative when empty with valve and that is in the roughly "normal" range (-1 to -3 pounds) for buoyancy for an empty steel tank. Anything more than 4-5 pounds negative when empty starts to become increasingly problematic.

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So the tanks that I described are 2.5 neg each, when empty? Which tanks, specifically, are the overly negative ones to likely avoid.

I got a little lost in your answer - although I appreciate the detail. Thank You.

 

[manni-yunk]

I found the chart. looks like -8.8 full and -1.3 empty. Not bad.

 

[Colliam7]

He made me an offer to buy one of his sets of double HP 100s. .... He said they need VIP and Hydro but be will get that done before sale.... 450 including tanks, bands, valve.

A fair price. You certainly couldn't buy a set of new 100s, and double them up, for that price. In reality, the number of times you find a set of used double 100s available for sale is relatively small. Unless there is something wrong with them - they do not pass hydro, for example - I would consider it a good price. I have paid $405 for a set of double PST 100s (with bands and manifolds), but paid an additional $75 for shipping. I have paid $400 for a couple of PST 100s without bands and manifolds that were available for local pick up. If they are available, and VIP and hydro are current, $450 is OK.

 

[Troutmaster]

If he is including a fresh hydro and VIP in the $450 price, that is a very fair price. If you don't want them I'll take them

 

[Leadking]

If the tanks get the usual cave country fill, I would pass.

The last thing you want is a set of tanks that have been "hydro'd" a few hundred times.

 

[DA Aquamaster]

A cave fill for HP or 3442psi tanks in N FL is about 3800 cooling to 3600 or so - pretty much like it is for 3AA 2400 psi tanks. Not really much of an overfill when you compare it to the service pressure.

The hydro pressure on a set of 3442 psi tanks would be 5163 psi. In contrast the hydro pressure on a set of 2400 psi tanks is 4000 psi, so your statement is only correct in regard to 2400 psi tanks and even then, it is questionable whether it is valid at all given the history of cave filled 2400 psi tanks passing their normal requalification tests over the last 10-15 years.