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.
JohnN:
. . . 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.