Cave Fills on LP tanks

[kelemvor]

I’ve posted before about the code and regulatory issues with overfilling cylinders and won’t rehash that. But from a straight common sense perspective I just don’t get this. Someone please explain the thought process behind getting lp85s and overfilling them instead of getting hp100s? If you need 200cf of gas why don’t you just get the correct cylinders?
Here are the dimensions to compare.
Faber LP85 at +10% 7” dia., 26” height, 31lbs empty, -6.7lbs full buoyancy, neutral buoyancy empty given you 85cf.
Faber FX100 7.25” dia., 25.4” height, 34lbs empty, -8.4lbs full buoyancy, -.6lbs empty buoyancy giving you 100cf.
Over filling a LP85 has no advantage over a correctly filled 100. The weight and bouyancy differences are negligible at best. A quarter less diameter?
For all of the talk of standards, doing things the right way and normalization of deviance I’m puzzled that many in the ‘cave community’ accept this practice.

LP85 filled to 3600 is 115cuft of gas.
FX100 filled to 3600 is 104cuft of gas. It's only 100cuft if you only fill it to 3442.
Why would you want less gas?

Personally, I do it with LP108's.
Lp108 filled to 3600 is 147cuft of gas.

However, those LP85's are a quite a bit lighter and easier to manage. That makes them an attractive compromise (vs the 108) in my opinion.

Mine are only 6 years now. They came back from their first hydro and still have the "+" rating. Even if they had failed hydro, the replacement cost would have been worth it... the only thing that gives me pause is that I can't easily find more Worthington lp tanks now days.

 

[Charles2]

Steel is really damn strong. I’d bet you are above 10,000 cycles before it fails hydro.

Agreed, steel is really damn strong. There is no cycle testing required in the 3AA specification for steel tanks, so I couldn't guess the number; but would not be surprised if it were even greater than 10,000.

Aluminum is really damn strong, too. The 3AL specification for aluminum tanks itself requires "Three samples must be subjected to 100,000 pressure reversal cycles between zero and service pressure or 10,000 pressure reversal cycles between zero and test pressure...without failure" also "Three samples must be pressurized to destruction and failure may not occur at less than 2.5 times the marked cylinder service pressure".

 

[WetRocks]

Over filling a LP85 has no advantage over a correctly filled 100. The weight and bouyancy differences are negligible at best.

The in-water bouyancy and trim characteristics are noticeably different when diving sidemount.
I started with HP100s because I didn't want to rely on a cave fill to get adequate gas volume. I dove them for a year and not knowing any better thought they were "ok". After my first dives with Worthington 85s I ordered 4 of them the same day and traded the 100s for 2 more, never looked back.

 

[Diver-Drex]

The in-water bouyancy and trim characteristics are noticeably different when diving sidemount.
I started with HP100s because I didn't want to rely on a cave fill to get adequate gas volume. I dove them for a year and not knowing any better thought they were "ok". After my first dives with Worthington 85s I ordered 4 of them the same day and traded the 100s for 2 more, never looked back.

I dive lp85 and Faber FX100s in sidemount. I don’t change anything between them and I don’t notice a difference. I dove Faber HP100s and did not like them. Which hp100s were you diving?

 

[2airishuman]

For all of the talk of standards, doing things the right way and normalization of deviance I’m puzzled that many in the ‘cave community’ accept this practice.

The practice predates the era when modern HP steels became readily available. PST introduced the first modern HP steel in 1987. Due to a series of production problems, availability was a problem on and off, particularly in larger sizes. I am unsure of the exact history, but I don't think it was reliably possible to purchase a new HP117, HP120 or HP130 without either advance planning or good luck until about 10 years ago.

Some cave dives are only possible with larger amounts of back gas, so the practice arose out of necessity, as one more risk to consider in a form of diving that requires acceptance and management of known risks in a way that recreational open-wider dives does not. It has since become commonplace due to the total lack of reported accidents that can be attributed to overfilling of 3AA steels.

 

[Rred]

IIRC the DOT specs also call for pressure testing at 5/3 of the rated pressure for all of those cycles. So assuming the tank is not damaged, filling it to 5/3 of the rated pressure (a whopping 5000 psi for a 3000 psi tank) is in theory within the ability of the tank. In practice...perhaps not quite.

 

[Diver-Drex]

@kelemvor - so filling the cylinder to 1.5 times it’s service pressure makes it comparable to larger tanks... that makes sense.

@2airishuman - so convenience and the fact that is hasn’t bit someone in the pants yet... And now that larger cylinders are readily available? How about staging bottles?

 

[PfcAJ]

I’ve posted before about the code and regulatory issues with overfilling cylinders and won’t rehash that. But from a straight common sense perspective I just don’t get this. Someone please explain the thought process behind getting lp85s and overfilling them instead of getting hp100s? If you need 200cf of gas why don’t you just get the correct cylinders?
Here are the dimensions to compare.
Faber LP85 at +10% 7” dia., 26” height, 31lbs empty, -6.7lbs full buoyancy, neutral buoyancy empty given you 85cf.
Faber FX100 7.25” dia., 25.4” height, 34lbs empty, -8.4lbs full buoyancy, -.6lbs empty buoyancy giving you 100cf.
Over filling a LP85 has no advantage over a correctly filled 100. The weight and bouyancy differences are negligible at best. A quarter less diameter?
For all of the talk of standards, doing things the right way and normalization of deviance I’m puzzled that many in the ‘cave community’ accept this practice.

Because it doesn’t matter.

Overfilling lp steel tanks is clearly fine.

It’s not normalization of deviance. It’s not a problem at all.

 

[kelemvor]

@kelemvor - so filling the cylinder to 1.5 times it’s service pressure makes it comparable to larger tanks... that makes sense.

Yes, you seem to be understanding the situation.

 

[Littlerayray]

I’ve posted before about the code and regulatory issues with overfilling cylinders and won’t rehash that. But from a straight common sense perspective I just don’t get this. Someone please explain the thought process behind getting lp85s and overfilling them instead of getting hp100s? If you need 200cf of gas why don’t you just get the correct cylinders?
Here are the dimensions to compare.
Faber LP85 at +10% 7” dia., 26” height, 31lbs empty, -6.7lbs full buoyancy, neutral buoyancy empty given you 85cf.
Faber FX100 7.25” dia., 25.4” height, 34lbs empty, -8.4lbs full buoyancy, -.6lbs empty buoyancy giving you 100cf.
Over filling a LP85 has no advantage over a correctly filled 100. The weight and bouyancy differences are negligible at best. A quarter less diameter?
For all of the talk of standards, doing things the right way and normalization of deviance I’m puzzled that many in the ‘cave community’ accept this practice.

You could give me up 1000's and I would still want them cave filled doesn't matter the size tbh the fuller they are the more and longer I can dive