Discrepancy in HP 120 sizes?

[Eric Sedletzky]

I just scored another HP 3442 E7120 steel tank (yay!!)
It seemed really long, so I pulled the boots of both it and my other 120 to do a comparison.
You can see that one is clearly longer. Both of them are stamped E7 3442 120 CF tanks.
The shorter one is a Worthington and the longer one is the Faber.
You can see the Faber has a bit longer stem up to the valve so I leveled it where the tank starts to go out, but look at the bottom, the Faber is clearly longer by 1-1/2” or so.
Both are 7-1/4” diameter so how can both be 120’s??
I’m not complaining one bit, I was totally stoked to find another HDG 120!, I’m just curious is all.

 

[Belzelbub]

That actually checks out according to the Manufacturer specs.

Faber HP120 HDG is 7.25" diameter and 29.1" long.
Worthington X7-120 is 7.25" diameter and 27.7" long.

Oddly, it appears that the Worthington holds a tiny bit more air at rated pressure. 120.6 cu. ft vs. 120 cu. ft.

With pressure of both at 3442, slightly thinner metal somewhere in the Worthington is the only thing that makes sense. The Worthington is actually a touch heavier. But, as I recall, the Worthingtons galvanized layer was a bit on the thick side, so that could be where the extra weight comes from.

 

[Badger7]

The short answer - they're not, but only vary slightly. I've been using various flavors of HP100 tanks, not HP120, so I don't know the differences on HP120 chapter and verse, but the 120 cubic feet rating is nominal, not precise.

Just did the briefest amount of digging, and I'm not sure they would both have E7 on them if they were a Worthington and Faber. I thought most/all of the worthington and faber tanks would have X7-100 on them, and the Worthingtons would have "M8004" on them as a mfr identifier while the faber would have "M8303" as an identifier (also typically an extra "faber made in italy" for good measure). I'd guess at least one of those is a PST, not a Worthington or Faber?

As a similar example - both Worthington and Faber HDG HP100 tanks are/were marketed as 100 cubic feet at 3442 psi, but the Worthington HP100 is a little shorter, slightly thicker walls, and holds 99.5 cubic feet of gas at 3442 psi, where the faber hp100 is slightly longer, slightly thinner walls, and holds slightly more than than 100 cubic feet of gas at 3442 psi.

Regardless of what you have there, as long as they keep passing hydro, those beautiful HDG cylinders should last a lifetime of diving, nice score!

You should figure out which one of those is more slightly buoyant at near-empty, and use that one for any weight checks, as I'm sure those two tanks will have slightly different buoyancy characteristics, but likely dive and trim exactly the same otherwise.

 

[Tanks A Lot]

This should be your Faber cylinder:

Water Capacity (L)	Diameter (mm)	Length (mm)	Working Pressure (Bar)	Empty Weight (Kg)	Empty Buoyancy Seawater (Kg)	Full Buoyancy Seawater (Kg)	Real Weight Seawater (Kg)	Empty Buoyancy Freshwater (Kg)	Full Buoyancy Freshwater (Kg)	Real Weight Freshwater (Kg)
15.3	184	745	237	17.8	0.29	-3.91	18.09	-0.23	-4.44	17.57

And this should be your Worthington:

Water Capacity (L)	Working Pressure (Bar)	Diameter (mm)	Length (mm)	Empty Weight (Kg)	REE (cc)	Buoyancy Full (Kg)	Buoyancy Empty (Kg)
15.4	237	184	711	17.2	94	-4.9	-0.9

The Worthington holds ever so slightly more air than the Faber does and according to their table should be a tad lighter. This means that the Faber will have slightly thicker walls as Belzelbub mentioned.

 

[Endler's]

If it's stamped E7, then it is a PST cylinder. The PST 3500 psi (skinny neck) cylinders are even shorter. Yours is in the middle lengthwise, but luckily the lightest!
.

 

[Eric Sedletzky]

Ok, here is what’s stamped on each cylinder in it’s enirety.
Tank 1.
TC-SU4957 - 230 BAR
DOT SP14157 3442 TP 5250
REE 94 X7 120
3770877 01^08 M8004
XS SCUBA

TANK 2.
FABER MADE IN ITALY
M8303 20/0031/ 054
01^20 TC-SU 7694-237 BAR
DOT - SP 13488 - 3442 PSI
REE 100 TP 5250 PSI
XS SCUBA HP 120

 

[Tanks A Lot]

M8004 is Worthington's M-Number.

They also manufacture under M5659, M4111, M4543 and M4875. The data I posted above for your Worthington cylinder was incomplete, as it does have alternative pressure and water volume data.

This is the full data:

Name	Water Capacity (L)	Gas Type	Working Pressure (Bar)	Diameter (mm)	Length (mm)	Empty Weight (Kg)	REE (cc)	Buoyancy Full (Kg)	Buoyancy Empty (Kg)	Alternative Water Capacity (L)	Alternative Working Pressure (Bar)
X7-120	15.4		237.32	184	711	17.2	94	-4.9	-0.9	15.3	230

Both your cylinders have the exact same internal volume. In the U.S. both are rated to the same pressure, elsewhere your Worthington is only rated to 230 bar instead of 237 bar.

 

[SpeedyJ]

I just scored another HP 3442 E7120 steel tank (yay!!)
It seemed really long, so I pulled the boots of both it and my other 120 to do a comparison.
You can see that one is clearly longer. Both of them are stamped E7 3442 120 CF tanks.
The shorter one is a Worthington and the longer one is the Faber.
You can see the Faber has a bit longer stem up to the valve so I leveled it where the tank starts to go out, but look at the bottom, the Faber is clearly longer by 1-1/2” or so.
Both are 7-1/4” diameter so how can both be 120’s??
I’m not complaining one bit, I was totally stoked to find another HDG 120!, I’m just curious is all.
View attachment 866946

Have you tried warming the one on the left up a bit? Or putting the one on the right in a cold room?

 

[Eric Sedletzky]

Have you tried warming the one on the left up a bit? Or putting the one on the right in a cold room?

No, but I have thought of putting them in a dark candle lit room with two glasses and a bottle of merlot and see if there might be a third baby tank in the morning.

 

[Belzelbub]

No, but I have thought of putting them in a dark candle lit room with two glasses and a bottle of merlot and see if there might be a third baby tank in the morning.

May be the only way of getting new galvanized steel tanks before too long.