HP Tanks - What's the point?

[Akimbo]

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in the uk the hp tanks are around 4500psi and the lp tanks 3500psi...

HP tanks in the US in the 1950s were 2,250 PSI and a lot of compressors could only reach 1,800. The cycle re-started in the early 1970s when 3000 PSI Aluminum cylinders were introduced. My all-time favorite are 300 Bar/4,351 PSI AGA 324’s, now Interspiro. I’m rooting for 6,000 PSI/414 Bar.

 

[johnmckenzie]

Thanks Bob. You always have great feedback. I especially liked that interesting point about the sidemount usage. Thanks for the OGD cudos too. I work with Don. Our mission is to give the best service of any dive shop in the country. And our fill policy is to guarantee a good fill and always show the customer the pressure on the gauge just before they leave the shop so they know it is right.

John

As in most things it depends on the application. I own a bunch of tanks ... Faber LP95's, Worthington HP100's, PST HP119's and PST HP130's. I use them according to the dive I'm planning to do. I have friends who dive the LP120's, and they wouldn't work well for me. They're long, heavier than my HP119's and 130's, and they don't trim out nearly as well. I use the HP100's primarily for sidemount diving. When I started sidemount, I used LP95's, because I already had them and they give me enough air for almost any dive I'd want to do. But once they get below about 1000 psi they tend to get butt-light ... so they don't work well for that application. The HP100's don't have that problem, plus they're smaller-diameter and less heavy, which make them easier to manage getting into and out of the water in a sidemount rig. On the other hand, the HP95's work well for training dives or just toodling around the dive site.

If your issue with HP cylinders is not getting good fills, then I'd suggest you need to find a shop that can accommodate them. Lord knows there are plenty in the Puget Sound area that do. Since you're in Kingston, I'd recommend Octopus Gardens in Pt. Townsend ... Don knows how to fill a tank properly.

Oh, and if you're really unhappy with that HP tank, go post a note on NW Dive Club forum looking for someone who'll trade with you for a comparable LP cylinder ... I think you'd get several offers.

... Bob (Grateful Diver)

 

[Colliam7]

I am asking for some intelligent dialogue on this topic for an article I am composing. . . .
I keep thinking why did I get talked into this HP tank. If I had an LP 85 (2400 psi), I could fill from the banks in minutes and never have to boost. I could always get full fills wherever I travel.

I see the point - a quick fill is probably easier with a LP cylinder. But, if what you want is 85 cf of gas, you can also get that with a quick fill of an HP100.

. . . that LP tank will only continue to hold 85 cu-ft if you can keep its "+" rating . . . Compare to a HP100. 2" shorter, only 2 lbs heavier empty (full the extra air will add about 1 lb), about the same buoyancy characteristics and a whole lot more gas.

Or, slightly more gas (89 cf) than a LP85, even if filled to only 3000 psi, which should not be a problem. (If a shop has a problem filling a cylinder to 3000 psi, but has no problem filling it to 2640 psi, then the shop's issues are beyond a discussion of HP vs LP cylinders.)

Now, although you don't mention it, cost could be a 'CON' factor. If you get a cylinder from Scuba.com, you will pay $325 for a LP85, but you will pay $350 for a HP 80, and $395 for a HP 100.

I am not sure what intelligent dialogue you are looking for. From my perspective, the cons you mention with regard to HP cylinders are not particularly weighty. So, my answer to the question is, 'No, the cons DO NOT outweigh the pros.' The choice of a cylinder is commonly based on factors such as buoyancy and trim characteristics, external dimensions (length and diameter), weight, and capacity. So, while 'size' is one factor, it is by no means the only factor in choosing a cylinder. Some divers prefer the buoyancy and trim characteristics of HP cylinders, some prefer the characteristics of LP cylinders, and some have different preferences for different applications (singles vs doubles, back mount vs sidemount, etc.). Even the manufacturer can make a difference, and the buoyancy / trim characteristics of cylinders vary across product lines. I happen to prefer HP cylinders for most applications (and I happen to prefer my PST HP cylinders), but I see no problem with someone else preferring LP cylinders. I see individual preferences as far more influential that the particular pros and cons you mention.

As for the cons you mention:

>>I found that some shops do not even have HP compressors. <<

There are probably some shops, somewhere, that don't. They should probably invest in contemporary equipment or get out of the dive shop business.

>>Even shops that have HP compressors do not really like HP tanks. That last 400 psi create a lot of wear and tear on the compressor and the fill system. <<

I haven't encountered shops that 'don't like' HP cylinders. I have to admit, if I took a cylinder to a shop for a fill and they said, 'Well, we really don't like HP cylinders', I would have to ask them what that meant. Does it mean they won't fill it? Or, they will fill it, but frown while they are doing it? Or will they charge more to fill it? That statement seems somewhat nebulous.

We fill HP cylinders in our shop all the time. I have never heard the owner, or the shop manager, express concern about particular the 'wear and tear' on the compressor and fill system associated with filling HP cylinders. And, our compressor doesn't seem to have mechanical problems with any frequency at all. We are a dive shop, we are in business to provide gas fills, among other things. If there is particular 'wear and tear' on our compressor, it comes from having to run the compressor so much in the summer time to keep the banks full in order to fill a whole lot of cylinders, because for some reason people seem to want to dive more in warm weather. But, in the summer, it gets really hot outside and we don't want to run the compressor during daylight hours, so we run it virtually every night. That is some real 'wear and tear'.

>>If the shop is filling from banks, it means you are going to be boosting to fill the HP tanks which wastes a lot of extra air to run the booster and attain a fill pressure. <<

Well, that may be true if you have one set of banks, operating at the same pressure, and the banks begin to empty. We fill from banks. We have set up four banks, and 'cascade' our fills. We run the compressor to fill the banks to 4500 psi. When our highest pressure banks are running low, during times of high demand, we sometimes have to boost to fill even 3000 psi AL80 cylinders. It is part of doing business (that also means we will run the compressor to refill the banks that night).

I am also confused by the 'wastes a lot of air' comment - where is the air being wasted?

>>Many shops in our are will just not give you a full fill (after cooling) or want you to leave it over night if you want a full fill. <<

OK, so the issue is that a customer doesn't want to leave a cylinder overnight, and make a second trip to the shop. I can see that. So, why don't the shops fill to service pressure (or slightly higher), put the cylinder in a water bath for a few minutes to cool it, and then top off to 'full' - IF the customer wants to wait for the cylinder rather than leaving it? Yes, it takes a few extra minutes but the customer doesn't have to come back. And, they can get a full fill. Maybe, I am missing something in the comment, though.

>>Theoretically the higher presser is going to put more strain on you regulator and hp hoses. <<

Are you aware of any data to support that this is an actual issue? I am not. I see statements like this from time to time, but I nave never seen any factual support to demonstrate that this is real.

>>Some older yokes are not even certified to be used on HP tanks. <<

But are used on them nonetheless, without problems.

I just don't see the 'cons' you outline as being strong arguments against HP cylinders.

 

[Randy g]

I use LP simply because I can get 3500-3600 psi fills regularly in my LP120's which equates to about 180 cf of gas and the LP 95's at 3600 sits at about 140 cf of gas. If the dive calls for more gas then I use my twin LP108's.

I would only use HP tanks if/when I start side mounting. LP tanks make sense to me!

 

[tomfcrist]

If HP tanks didnt exist, my LPs wouldnt ever get "accidentally filled to 3600psi.......and that would be a tragedy.

 

[tracydr]

I too have difficulties getting proper fills on my HP 80s at my LDS. They tell me they can't go over 3,000 PSI on their compressor. I'm okay with that because they give DMs and instructors free fills. I could always go to the other dive shop,if I really needed full tanks.
The Catalina Dive Park fill station doesn't give me a good fill,either, which is not so great and I really wise I'd get a good fill there since diving on less than a full 80 in cold water makes for a short dive. Plus, my husband dives an LP 85 and gets a nice fill on his which gives a pretty wide discrepancy, which is usually okay but not always when on a colder dive.
I love my HP 80s on some of the CA dive boats when I do get a proper full. I'm so used to diving with 65-70cu ft of air that I feel like I can go all day on a nice fill. I also love the size and buoyancy characteristics when diving a drysuit with my tanks. Not for everyone, I realize. My husband much prefers his LP tank.
I'll probably go to sidemount ( maybe doubles but unlikely) and I'm trying to decide which tanks will be best. I'd sure like to use something we already have, since we have a huge amount of tanks in our garage.
I'm 61" tall so the smaller tanks are useful. I dive AL 63 for warm water.

 

[drbill]

I used to dive an HP120 almost exclusively. Why? Because I could get 2-3 dives out of a single fill and I needed less weight on my belt than I did with an Al 80. I was also diving deeper (180-200 fsw) than I do today so I got more bottom time. Another benefit of the HP was the DIN valve (before convertibles became popular) so I had a more reliable reg-to-tank connection.

Unfortunately getting a full 3500 psi fill was not always possible, at some shops and on some dive boats. The reason I don't dive my HP120s today (and stick with my neutral buoyancy Al 80s from the 70s) is that one failed hydro due to overexpansion (frequent hot fills at one shop) and the other failed VIP due to rust (from wet boat fills).

 

[Nwcid]

LOTS OF CONS
With and HP tank (e.g. 3450 psi) I found that some shops do not even have HP compressors. Even shops that have HP compressors do not really like HP tanks. That last 400 psi create a lot of wear and tear on the compressor and the fill system. If the shop is filling from banks, it means you are going to be boosting to fill the HP tanks which wastes a lot of extra air to run the booster and attain a fill pressure. Many shops in our are will just not give you a full fill (after cooling) or want you to leave it over night if you want a full fill.

I only have any real experience with the compressor out dive team uses which is a 15cfm, can't recall the brand right now.

We have NO booster, use a bank, and have no problem filling to any point needed. Most of our guys have AL-80 tanks but I have AL-40's, LP-72's, AL-80's, HP-100's and HP-130's. Our bank is 6 tanks and the compressor is set to auto shut off at 4300 PSI. So if you keep your bank full not sure why you need a booster.

As far as being harder I know it takes more time and power to get to those pressures. What I don't understand is how it is harder on a 5000 psi to fill to 3500 psi or even 4000 psi then to use a 3000 psi (or whatever old compressors were rated for) to fill to 3000 psi.


When I dive singles I dive a HP-130 and the GF dives an HP-100. Because of our SAC this makes us almost PSI out the same. When I am diving doubles I use the LP-72's as they are much lighter then the HP-100's and if I want to give them a good fill I have just as much gas.

 

[nimoh]

I only have any real experience with the compressor out dive team uses which is a 15cfm, can't recall the brand right now.

We have NO booster, use a bank, and have no problem filling to any point needed. Most of our guys have AL-80 tanks but I have AL-40's, LP-72's, AL-80's, HP-100's and HP-130's. Our bank is 6 tanks and the compressor is set to auto shut off at 4300 PSI. So if you keep your bank full not sure why you need a booster.

As far as being harder I know it takes more time and power to get to those pressures. What I don't understand is how it is harder on a 5000 psi to fill to 3500 psi or even 4000 psi then to use a 3000 psi (or whatever old compressors were rated for) to fill to 3000 psi.


When I dive singles I dive a HP-130 and the GF dives an HP-100. Because of our SAC this makes us almost PSI out the same. When I am diving doubles I use the LP-72's as they are much lighter then the HP-100's and if I want to give them a good fill I have just as much gas.

The problem with that is you have more reserve than her, and you need to be sure that she has enough gas to share with you if necessary.

 

[Nwcid]

The problem with that is you have more reserve than her, and you need to be sure that she has enough gas to share with you if necessary.

Correct. So it depends on what kind of dive we are doing to know if that matters or not.