Filling High Pressure Tanks vs Low Pressure Tanks

[sandysisland]

Hello,

I've been diving since 2009 and recently have been getting my tanks filled at XYZ. I have a HP Steel 80 that fills to 3442 psi. I went to go and pick up my tank and the person working the counter asked if she could 'check the gauge'. I said 'sure why not?'. Seeing that my tank was not filled up all the way she suggested that I get it filled just a little bit more. I noticed that when she went to go and fill it it was on a low pressure hose rather than a high pressure hose.

Does it matter that my tank is a high pressure? Now, is there ANY difference in the air quality. I don't assume so. But in the back of my head I wonder.....

Thank you Scuba board.

Sandy

 

[pocky21]

The only advertised difference you will see in "air quality" is that of air rated for oxygen service (meaning filtered of hydrocarbons and other undesirable contents - used for nitrox filling or when putting "air" into a nitrox tank), and standard compressed air which isn't filtered to the standards of oxygen service. It is often referred to as "O2 clean" air. It only becomes an issue when non O2 clean air is placed into a cylinder cleaned for oxygen/nitrox service, in which case that cylinder will need to be re-cleaned after the exposure.

Now, the common issue with High pressure tanks is getting enough air into the cylinder. The shop may fill to the tank's rated pressure, but if they do not allow the tank time to cool down, the pressure will have dropped to 3000-3200 or more. This is why it's recommended to leave your tanks at the shop for a day or two, that way they can top off the tank to ensure you get a full fill to 3442.

The hoses that a fill station uses will (should be) rated to pressures well above 3500psi - typically in the 4000-5000psi range in my experience. If she was indeed using a low pressure hose like your regulator uses, which IIRC is rated around 400psi, I would have been taking a few very large steps back and preparing for the show. I'm not exactly sure what you meant when you said she was using a low pressure hose - note that both rubber coated hoses and braided stainless steel hoses come in a variety of working pressures, one does not necessarily indicate a higher working pressure than the other.

In the end, just be sure that the shop knows that the tank is a high pressure tank. Call ahead and ask if they fill these types of tanks. For best results, ask if you can leave the tank overnight so they can top it off once the tank cools down. This is what I often do with my double HP100's. Aside from that, you should have no issues whatsoever - happy diving!

 

[CurtSchu]

I have never seen two sets of hoses on a fill station pertaining to pressure. Shops that bank nitrox might have separate hoses for the different banks. All fill lines would normally be 4000-5000 rated

 

[Imbodie]

Ok... so not to start a war of HP vs LP.... but if its such an issue to get fills for HP tanks... why not just buy LP tanks.... if an LP 95 has the same amount of air at 2450(or whatever the exact number is) then why buy a HP100 tank that HAS to be taken to 3440 to have 100 cubic feet of air?? I'd much rather have my LP 85's and KNOW I can at least get them filled to rated PSI ANYWHERE... and possibly get "cave" fills in them up to 3000 (I know some people go even higher on a cave fill) and even have that much MORE breathing gas..... Whats the benefit of HP tanks??

 

[Dr. Lecter]

I noticed that when she went to go and fill it it was on a low pressure hose rather than a high pressure hose.

Does it matter that my tank is a high pressure? Now, is there ANY difference in the air quality.

I have no idea what you're trying to say... is it that XYZ usually fills HP tanks from one fill whip hose and LP tanks from another fill whip hose? Regardless, pressure and air quality have nothing to do with eachother.

Ok... so [-]not [/-]to try my best to start a war of HP vs LP.... [blah blah blah] Whats the benefit of HP tanks??

They weigh less, trim out better, and are perfectly fine in terms of volume if you have a proper fill station.

 

[JohnN]

Ok... so not to start a war of HP vs LP.... but if its such an issue to get fills for HP tanks... why not just buy LP tanks.... if an LP 95 has the same amount of air at 2450(or whatever the exact number is) then why buy a HP100 tank that HAS to be taken to 3440 to have 100 cubic feet of air?? I'd much rather have my LP 85's and KNOW I can at least get them filled to rated PSI ANYWHERE... and possibly get "cave" fills in them up to 3000 (I know some people go even higher on a cave fill) and even have that much MORE breathing gas..... Whats the benefit of HP tanks??

Have you ever tried to lift a LP120?

My HP120's are a load, but manageable. Not so with the LP variant. . .

 

[chrpai]

Ok... so not to start a war of HP vs LP.... but if its such an issue to get fills for HP tanks... why not just buy LP tanks.... if an LP 95 has the same amount of air at 2450(or whatever the exact number is) then why buy a HP100 tank that HAS to be taken to 3440 to have 100 cubic feet of air?? I'd much rather have my LP 85's and KNOW I can at least get them filled to rated PSI ANYWHERE... and possibly get "cave" fills in them up to 3000 (I know some people go even higher on a cave fill) and even have that much MORE breathing gas..... Whats the benefit of HP tanks??

Around here it can be difficult to get the + rating and + fills. At 2400psi the 95 is only an 86. It can also be difficult to get the 3442 on an HP100. That said, the HP tanks are 4lbs lighter (8lbs for doubles). They are both "short" tanks that can be a problem trimming out for some.

 

[Imbodie]

I have no idea what you're trying to say... is it that XYZ usually fills HP tanks from one fill whip hose and LP tanks from another fill whip hose? Regardless, pressure and air quality have nothing to do with eachother.

They weigh less, trim out better, and are perfectly fine in terms of volume if you have a proper fill station.

HEY... I didn't say that...

I do know that I really like my LP85's over Al 80's.... And though I know these are "LP" I don't mind the shop filling them to 3k... though I tend to get a little upset if they give me a real "CAVE FILL" the additional 600psi really isn't that big of a deal in the grand scheme of things... But I think anything over 3k is actually harder on your regulators... regardless of the tank rating...

---------- Post added August 27th, 2013 at 09:39 PM ----------

Around here it can be difficult to get the + rating and + fills. At 2400psi the 95 is only an 86.

That totally goes against everything I've been told... of course AL 80's only being 75 or 76 CuFt messes me up too... I thought the Steel tanks were truer to their actual size...

 

[pocky21]

Ok... so not to start a war of HP vs LP.... but if its such an issue to get fills for HP tanks... why not just buy LP tanks.... if an LP 95 has the same amount of air at 2450(or whatever the exact number is) then why buy a HP100 tank that HAS to be taken to 3440 to have 100 cubic feet of air?? I'd much rather have my LP 85's and KNOW I can at least get them filled to rated PSI ANYWHERE... and possibly get "cave" fills in them up to 3000 (I know some people go even higher on a cave fill) and even have that much MORE breathing gas..... Whats the benefit of HP tanks??

I have yet to see a shop that does not fill to 3500, but some do request advance notice or leaving the tanks with them to top the banks off. The last shop I worked for would often have the last bank at 3000-3200 before they kicked the compressor on. If a shop didn't fill to 3500, I would begin to question other things, including their filtration system, and likely would not go to them for fills.

As for LP vs. HP - most of it lies in dead weight, buoyancy, and trim. My HP100's are by far my favorite tanks diving dry. I had a HP80 for a while, but it was simply too short and hard to trim out, however many women prefer them. Now my LP104, aka the "lumbar's scourge", tends to sit in the closet and do nothing - there's simply no situation where it's beneficial for me to use it. It's big, heavy, trims out terribly, and 90% of the time I'm limited by NDL anyway. The gas does nothing for me as a single tank. The thought of wearing two of those things only makes me shudder.

There are situations where I can definately argue the use of LP tanks, as the situation/location/objective are better suited for the added gas, but one needs to consider their own diving and equipment preferences as well. For me, ALL of my diving is currently suited best by AL80's or my HP100's.

 

[chrpai]

That totally goes against everything I've been told... of course AL 80's only being 75 or 76 CuFt messes me up too... I thought the Steel tanks were truer to their actual size...

An LP+ tank is only it's rated capacity when filled to 110% of it's service pressure. An LP95 is 95 at 2640. At 2400 it's 86 and change. At 3000psi it's 108.

Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan

---------- Post added August 27th, 2013 at 08:48 PM ----------

I have yet to see a shop that does not fill to 3500, but some do request advance notice or leaving the tanks with them to top the banks off. The last shop I worked for would often have the last bank at 3000-3200 before they kicked the compressor on. If a shop didn't fill to 3500, I would begin to question other things, including their filtration system, and likely would not go to them for fills.

Around here Windy Point usually doesn't have that much pressure and I've been told that the M/V Fling (Flower Gardens) doesn't either. There was a big fuss from some divers complaining that the boat policy charged a surcharge for 100+ tanks but then didn't actually fill 100cf in the tanks.