PST: E7-80 Specifications?

[Sik_Z33]

I can get consistent information for the true specs of my PST E7-80 Hp cylinder. which specs on these two charts is the correct one?

PST Specs

Scuba cylinder specs

 

[redacted]

PST credibility come under question based on their scaling of the E7-100 capacity as a function of pressure. But it could just be how they chose to round off results.

 

[Luis H]

My wife has two E7-80.

Here is the data I measure for both of them.

Tank I
Weight with valve and tank boot: 35.6
Measured weight in fresh water (tank full): 8.1 Lb
Calculated weight in salt water (based on fresh water weight): 7.4 Lb
Average wall thickness (measure using ultrasound measurements on 12 places): 0.192 in
Average bottom thickness (measure using ultrasound measurements): 0.254 in
Measured water capacity of tank: 22.74 Lb (of fresh water at about 75 degrees F)
Volume of water: 0.3644 cubic feet
Air capacity when filled at 3442 psi (Based on measured actual tank volume): 85.3 cu ft of air


Tank II
Weight with valve and tank boot: 35.7
Measured weight in fresh water (tank full): 8.3 Lb
Calculated weight in salt water (based on fresh water weight): 7.5 Lb
Average wall thickness (measure using ultrasound measurements on 12 places): 0.195 in
Average bottom thickness (measure using ultrasound measurements): 0.254 in
Measured water capacity of tank: 22.65 Lb (of fresh water at about 75 degrees F)
Volume of water: 0.3630 cubic feet
Air capacity when filled at 3442 psi (Based on measured actual tank volume): 85.0 cu ft of air

Note: the water volume did not include the volume in the threaded neck since that volume will be partially filled by the brass valve.

The measured air capacity was a bit of a surprised, but I have checked my measurements and numbers a few times.


I have measured a few steel 72 and the ones that I have measure range from 70.8 cu ft to 71.4 cu ft. At some point I will get around to measure the rest of my steel 72.

 

[Leslie Sapp]

Luis, Have you done any calculations for E-7 100's?

 

[Luis H]

Sorry, I have not taken any measurements or have any 100 cu ft tank to take measurements from.

 

[Jeff_O]

My wife has two E7-80.

Here is the data I measure for both of them.

Tank I
Weight with valve and tank boot: 35.6
Measured weight in fresh water (tank full): 8.1 Lb
Calculated weight in salt water (based on fresh water weight): 7.4 Lb
Average wall thickness (measure using ultrasound measurements on 12 places): 0.192 in
Average bottom thickness (measure using ultrasound measurements): 0.254 in
Measured water capacity of tank: 22.74 Lb (of fresh water at about 75 degrees F)
Volume of water: 0.3644 cubic feet
Air capacity when filled at 3442 psi (Based on measured actual tank volume): 85.3 cu ft of air


Tank II
Weight with valve and tank boot: 35.7
Measured weight in fresh water (tank full): 8.3 Lb
Calculated weight in salt water (based on fresh water weight): 7.5 Lb
Average wall thickness (measure using ultrasound measurements on 12 places): 0.195 in
Average bottom thickness (measure using ultrasound measurements): 0.254 in
Measured water capacity of tank: 22.65 Lb (of fresh water at about 75 degrees F)
Volume of water: 0.3630 cubic feet
Air capacity when filled at 3442 psi (Based on measured actual tank volume): 85.0 cu ft of air

Note: the water volume did not include the volume in the threaded neck since that volume will be partially filled by the brass valve.

The measured air capacity was a bit of a surprised, but I have checked my measurements and numbers a few times.


I have measured a few steel 72 and the ones that I have measure range from 70.8 cu ft to 71.4 cu ft. At some point I will get around to measure the rest of my steel 72.

I know it is old thread. I have Pressed Steel Cylinders brand E7 80. I thought great when I got it December 2005. It was the size of an aluminum 50, but held what I think was 80cf at the max pressure 3340. Better for me so it doesn't bump my neck or lower back. Great and weight was right. What in this 2022 post I am looking to see if there is the same kind of tank specs available now. I note that they cost no longer $205 as it were back then in 2005. The ones I see now are noticably heavier and I wonder why. Would you think that the tank made with less metal is it and then how do feel about it's safety? I keep having it hydro to keep getting visual and fills.

 

[inquis]

The measured air capacity was a bit of a surprised, but I have checked my measurements and numbers a few times.

Since this has resurfaced, I'll make a comment. I suspect @Luis H was surprised by the calculated air volume of ~85 cuft differing from the rated volume of 80 cuft based on the name (HP80). The non-ideal nature of air mandates a correction factor (the so-called "Z Factor"), which becomes more significant at higher pressures. At 3442 psi of air, the factor is 1.0532. Therefore, the actual air volume contained at rated pressure would be 85 / 1.0532 = 80.7 cuft, which is essentially the rated volume.

On the other hand, the common AL80 cylinders have an ideal capacity of ~80 cuft, but an actual air volume of 77.6 cuft (Z-factor at 3000 psi is 1.032). An LP85 steel is similarly shortchanged and only holds 81.1 cuft at its rated 2640 psi. Even worse is the ideal capacity is only 82.5 cuft. Gotta love the marketing department folks!

Hope that helps someone...