LP vs HP question

[rds912]

I have been on 4 of the southern cal dive boats. I currently have an AL 80 which sems to make it to only 2700-2800 psi on the fills in between dives. So far I have not seen the deck hands changing the psi of the fills everyone no matter what tanks gets the 2800psi hot fill. So I dont want to "break" the rules, I just want to end up with 100cf of air. is a 2700-2800 psi fill on a low pressure tank that bad, or just be safe and pick an HP tank that would end up with 100cf @ 2700psi. I appreciate all the input and it seems there are 2 very different camps on this subject, I'm just trying to gather as much info as possible before spending $350.00 on a tank. Thanks

 

[DA Aquamaster]

A 200-300 psi drop in pressure is common on a tank filled directly off a compressor as the air going into the tank is warm. The same thing is true with a faster fill off na airbank as the faster increase in pressure in the tank generates heat.

Obviously "overfilling" the tank by 300 psi to offset the loss of pressure that will occur as it cools to room temp is the most expedient way to address the problem - and it is not actually illegal as the regs require the tank to be at service pressure once it cools to 70 degrees/room temp.

On a boat that is maybe 1 more minute on the compressor to get a good fill, but some operators stop at the service pressure and will not exceed it even to compensate for normal loss of pressure due to cooling.

 

[DA Aquamaster]

I'm not talking massively overfilling, and I'm certainly not in Florida. A "hot" 3000psi fill puts the LP95 at 2700psi. Been there, done that. I've been on quite a few California dive boats and this is very common. Even the boats with LP Steels fill theirs to 3000 psi, so my statement stands.

A local captain said to us during a dive briefing, "these are low pressure 80 cubic foot tanks, but somehow they got filled to 3000 psi. Oops. If you're worried about it, bleed some pressure off before you put your regulator on."

And I don't care who you are, if you buy a high pressure 130 cubic foot tank, you're going to feel short changed when you see it "only" has 2700 psi in it.

3000 psi in a 2400 psi service pressure tank is a 125% overfill. 2640 psi is the "normal" 10% overfill allowed for a plus rated 3AA steel tank.

So at 3000 psi you are only half as overfilled as at 140%, but you are still 15% over the amount allowed in a plus rated 2400 psi steel tank.

Is it acutely dangerous - probably not. But it is in violation of the regs and most shops outside N FL will not do it.

Perhaps more importantly, if your 2400 psi tank has a burst disc designed for a 2400 psi service pressure, the overfill can have an adverse affect on an aged burst disc that has seen numerous cycles. The result can then be a burst disc failure during the fill - leaving you tankless, or alternatively in the water after the disc cold soaks which occurs about the same time you reach max depth.

Most divers who intentionally have their tanks overfilled either double the burst discs or use one designed for a 3000-3500 psi service pressure rather than 2400 psi (both practices by the way also violate the regs). So a well meaning captain overfilling a 2400 psi tank to 3000 psi without advising/getting permission from the diver first may not be doing a diver any favors.

 

[cmburch]

Last month I purchased 2 new HP130's on Craigslist for $250 each Vis 2/08 Hydro 9/07&11/07. You may find a good deal somewhere.

For the 100CF at about 2800psi the HP120 and HP119 would be in that range.
Type - Weight Empty Height Buoyency Empty Diameter
HP120 - 38lb empty, 28", -2lb, 7.25"
HP119 - 42lb empty, 24", -2lb, 8"
LP95 - 42lb empty, 23.7", - 3lb, 8"

They all have the Pro valve. It seems that the only difference is that the LP95+ is only rated to 2640. Why go with the limited LP95 when the HP119 is very similar and can hold more cf at higher pressure? I don't know why the LP would be considered unless it was cheaper. I advise trying out a lighter tank before purchasing something heavier that may not meet your future needs. The HP100 is my favorite tank and the HP120 is lighter but it may be too long.

 

[Teamcasa]

I have been on 4 of the southern cal dive boats. I currently have an AL 80 which sems to make it to only 2700-2800 psi on the fills in between dives. So far I have not seen the deck hands changing the psi of the fills everyone no matter what tanks gets the 2800psi hot fill. So I dont want to "break" the rules, I just want to end up with 100cf of air. is a 2700-2800 psi fill on a low pressure tank that bad, or just be safe and pick an HP tank that would end up with 100cf @ 2700psi. I appreciate all the input and it seems there are 2 very different camps on this subject, I'm just trying to gather as much info as possible before spending $350.00 on a tank. Thanks

I too dive on many SoCal boats. I use a HP100 and usually get a +3000 fill, rarely a full fill. Mainly due to the fact that I ask politely and always tip directly to the deck hand and to the jar.

I also have 3500 in yellow sharpe on the top of the tank.

Most any boat fill is going to be wetter than a shop fill. If I make a half dozen trip I get the tanks vis’d.

 

[dannobee]

Why go with the limited LP95 when the HP119 is very similar and can hold more cf at higher pressure? I don't know why the LP would be considered unless it was cheaper.

The low pressure tanks are "3AA" and not "E" tanks. If the company goes out of business or doesn't renew the exemption, you're SOL when it comes hydro time. After PST went belly up, there was quite a discussion here and other places on what would happen to all of those tanks that couldn't get re-hydroed. It caused quite a scare until PST magically resurfaced.

 

[cmburch]

The low pressure tanks are "3AA" and not "E" tanks. If the company goes out of business or doesn't renew the exemption, you're SOL when it comes hydro time. After PST went belly up, there was quite a discussion here and other places on what would happen to all of those tanks that couldn't get re-hydroed. It caused quite a scare until PST magically resurfaced.

Thank you for the information. Now I think I may understand what 3AA and E stands for. And the difference between the LP and HP tanks.

 

[dannobee]

3000 psi in a 2400 psi service pressure tank is a 125% overfill. 2640 psi is the "normal" 10% overfill allowed for a plus rated 3AA steel tank.

So at 3000 psi you are only half as overfilled as at 140%, but you are still 15% over the amount allowed in a plus rated 2400 psi steel tank...

Come dive off of some of our boats sometime. You'll understand that 3000 psi = 2700 or less when it cools off. The LP95's rating with a "+" is 2640. Damn near perfect. Some of the dive boats (whose names I won't mention) have compressors that won't even make it much past 2500 psi HOT. Let's see who has more gas, the guy with the LP130 water heater, or one of those exempt HP100's. If you're diving one of those HP100's, I won't want to be your buddy, that's for sure.

And who exactly is it who monitors these fills for being "illegal?"

 

[cmburch]

Come dive off of some of our boats sometime. You'll understand that 3000 psi = 2700 or less when it cools off. The LP95's rating with a "+" is 2640. Damn near perfect. Some of the dive boats (whose names I won't mention) have compressors that won't even make it much past 2500 psi HOT. Let's see who has more gas, the guy with the LP130 water heater, or one of those exempt HP100's. If you're diving one of those HP100's, I won't want to be your buddy, that's for sure.

And who exactly is it who monitors these fills for being "illegal?"

No need to bash HP tanks like PapaBear rips Split Fins. My HP100 works great because my buddies use Al80's. I can suck up air chasing down a fish and still surface with more air than my buddies. If I was using an Al80, I would be the first one surfacing. Also it is a lot less weight when hiking down cliffs and less weight on my belt. A very streamline tank for hunting.

The HP130 is very similar to a LP95 in size and weight.
XS Scuba Worthington Steel Cylinder Specifications

I have two HP130's. So if I am diving with only 1 buddy, my buddy uses the other. I would only use these tanks for boat dives and easy access beach dives because they are MONSTERS.

 

[DA Aquamaster]

The low pressure tanks are "3AA" and not "E" tanks. If the company goes out of business or doesn't renew the exemption, you're SOL when it comes hydro time. After PST went belly up, there was quite a discussion here and other places on what would happen to all of those tanks that couldn't get re-hydroed. It caused quite a scare until PST magically resurfaced.

Well...it's true if a company such as PST went belly up that they would not apply for the renewal, but it's no big deal as anyone can file the same paper work to renew the exemption to get their tanks recertified. It's really not a big deal.