+ 10% and capacity

[Scotttyd]

I always thought a LP tank's capacity was based on the =10%, ie a LP95 was only 95 if it was filled to the 2640, not the 2400 original service pressure without the 10% rating, although a LDS tolday told me that it is 95 at 2400, who is right?

[gregor]

you are correct. this is the case for all tanks with the + rating as far as i know

[tonka97]

Originally Posted by Scotttyd

I always thought a LP tank's capacity was based on the =10%, ie a LP95 was only 95 if it was filled to the 2640, not the 2400 original service pressure without the 10% rating, although a LDS tolday told me that it is 95 at 2400, who is right?

Nice thread.

This information should be more available.

I purchased 2x HP100s, then learned that:

"No, they only have 100 cf when filled at 3442 psi, and very few dive shops have the capability to fill them at that higher pressure. I won't be getting 2 x 100 c.f. of gas."

If they are filled at 3000 psi (typical), I will have less gas than LP95s.

[BoomerNJ]

This is exactly why I went with LP95's... I will almost never get an under fill, most likely I will get an over fill to 3000, or at least a hot fill to 3000, in which case I'll get what would be the correct fill for LP95 which is around 2600 or 2700. Most local shops have no problem filling my LP95's to 3000 (cold), that way I have around 108cf (i forget what the actual cf is at that pressure, but it's more than 100cf)...

Only problem with LP95's is that they are 8.0 inch diameter tanks, which a lot of boats don't have racks that fit them. Not a huge problem, I'll just bungee them in, but it's there...

[BouzoukiJoe]

Scott,

you are almost right. Only problem is that many of the tank sizes are nominal sizes- sort of like an AL80 being 77.4 cu ft. Filling to rated pressure + 10% will give you the actual rated capacity which might be a coupla three cu ft different from the nominal rated capacity. Since their are different tank designs out there, you really have to look at each one separately.

FWIW I notice Scubatoys gives this information for the LP Worthington tanks in the tanks section of their online store.

Also, as far as I know nominal = actual rated capacity for all of the HP tanks out there.

[stairman]

95 at 3000psi=108c.f.I have no problem getting my 95's filled to 3600 psi.I guess it depends on where you go.Mine are also double disked for overhead penetration.95 at 3600psi=130 cf x 2 =260 cf.[86cf for penetration]174 cf for exit and reserve.

[BoomerNJ]

Originally Posted by stairman

95 at 3000psi=108c.f.I have no problem getting my 95's filled to 3600 psi.I guess it depends on where you go.Mine are also double disked for overhead penetration.95 at 3600psi=130 cf x 2 =260 cf.[86cf for penetration]174 cf for exit and reserve.

Thanks stairman for the info. I truly don't see cave in my future, I don't like confined spaces (and I've been a firefighter for 19 years, I can do it, but I wouldn't for recreational purposes, lol...). I've never asked my LDS to go to 3500 on my 95's, they just always go to 3k on 'em without even asking. Some of my dive buddies though can breath a HP100 for two days & still come up with 1000 left, which drives me nuts. So maybe when I know they're coming out, I'll look into 3500psi fills... lol... Thanks again for the info!

[CompuDude]

Yes, LP tanks come with a + rating (generally) to allow 10% overfills from 2400 (meaning fill to 2640). This is where their rated capacity comes in. Retarded system, IMO, but that's how it is. If you do not have your tank tested at a hydro facility that confirmed the plus rating, technically your tank is now only rated to 2400 and you can no longer fill to 2640, only 2400.

All other tanks are rated to fill pressure with no overfill, such as 3000psi for aluminum, 3442-3500 for HP, etc., with none of that overfill BS.

Incidentally, the LP95 is almost the exact same tank as the HP119, if you look at the specs. Squirt 2640 in and you have (essentially) 95 cf in each. Put 3442psi in them and you have 119cf in each. So you have a choice... underfill an HP119 (completely safe and well within design specs), or overfill an LP95, and go outside design specs. Plenty of anecdotal evidence that such overfills are not likely to cause a problem, but you ARE going outside spec nonetheless... and if you start counting on those overfills, you're going to be hurting when you come across a shop or boat that will only fill to rated pressure.

Personally, I'd rather buy an HP tank that holds enough gas even with an underfill than consistently overfill the LP tank.

[Jack Hammer]

my steel hp100 filled to 3000psi still gives me ~87cf air. It weighs about the same as a al80(77.4cf) and has much better bouyancy and is physically smaller, almost three inches shorter. It has about the same outer dimensions as an al63.

Most people I dive with are using rental al80's. So I finish most dives with ~1/2 tank of air left, lots of reserve. Getting filled to 3000psi hasn't been an issue for me when it has happened. I'm ok with my tank being more like a steel "90" (refering to capacity at 3kpsi), it's still plenty of air for the dives i'm using it for so far.

Like Compdude said, you need to look at the outer dimensions of a tank to compare a HP to a LP, not the volume. Then look at the actual weight and bouyancy against your air needs to determine which size is better for you (don't forget price). Just looking at the CF capacity does not give you an apples to apples comparison.

Jack

[cummings66]

It is definitely true that you need the + to get rated capacity, but why those chose to do it that way is beyond me. I think they did it because it sounds better.