Short Fills In HP Tanks

[LAP57]

I am in the process of replacing my older steel Genesis tanks with new steel tanks. I dive a variiety of gear and want to have all my tanks set up for yoke valves. I like HP tanks and have done some searches through the forums and I am still convinced that they are the correct choice for me.

I have one question left and I don't have enough first hand information to derive an answer. Are there issues with getting short fills on HP tanks? In my area all the shops are set up to handle 3500psi. On boat dives I bring full tanks so I have never needed a fill on board (this must be an issue on live aboards because the small day charters I have used don't fill tanks). I have read though that in certain areas the shops aren't set up to support HP fills or that the compressors on some boats can't handle this. Is this really an issue? If so how often have you encountered this problem. Is this a matter of getting 3400 instead of 3500 or is it a matter of getting 3000 instead of 2500?

Thanks.

 

[fppf]

I personally have not seen a dive shop yet that can't fill 3500 PSI cylinders.

I would think almost all places can fill to 3000 PSI because the AL80 is the work horse of the industry. So at most you will only be loosing 500 PSI and unless your using HP80's you will still have more gas then an AL80.

To add to that, the LP series of cylinders and HP series are almost paired in physical size. IE a LP95 is close in size to a HP119. So if you buy the same physical size cylinder in a HP version, if you get a short fill for the HP, or what would be a normal fill on the LP you will have the same amount of gas. But with the HP cylinder you have the added benefit of getting more gas with the full HP fill.

 

[Fish Flayer]

I have found that shops that fill high volumes of tanks quickly hot fill tanks to 3500 then they cool to room temp and are only 3000-3100 yes its only 400psi but if you got an al80 with a 2500 fill you would be upset. I personaly have 5 hp 130's and am looking to swap to lp 120/130's

 

[fppf]

I have found that shops that fill high volumes of tanks quickly hot fill tanks to 3500 then they cool to room temp and are only 3000-3100 yes its only 400psi but if you got an al80 with a 2500 fill you would be upset. I personaly have 5 hp 130's and am looking to swap to lp 120/130's

This is a function of the shop filling the cylinders. There is a large volume of air being compressed in, and it is at a higher pressure, which generates more heat. Steel cylinders don't shed there heat as fast as aluminum.

You can handle this two ways, either wait for the cylinder to cool which most don't as you find out. Or you can fill the cylinder to about 3,800 to 3,900 depending on how fast you filled it. This is perfectly legal because you are not over filling the cylinder. The pressure rating of a cylinder is based at 70 degrees. When the cylinder is hot the pressure is going to be higher and this is accounted for. So when the cylinder cools down to 70 degrees you should have the proper fill pressure.

 

[DA Aquamaster]

A X7-100 100 cu ft tank weighs 33 pounds and holds:

99.5 cu ft at 3442 psi
95.4 cu ft at 3300 psi
86.7 cu ft at 3000 psi
80.1 cu ft at 2800 psi
76.6 cu ft at 2650 psi

So you have to get down to around 2650 to do worse than a full AL 80 that weighs about the same.

I also agree that most High pressure tanks have a similar sized LP equivalent. In terms of Worthington tanks, the X8-130 is nearly identical to the LP 95, but for an extra pound and an extra inch of height you can go with the X8-130.

An X8-130 weighs 43 pounds and would hold 114.5 cu ft if underfilled to only 3000 psi and an X8-119 weighs 42 pounds and would hold 107.2 cu ft at only 3000 psi.

A Worthington LP 95 also weighs 42 pounds and holds 93.3 cu ft at 2640 psi. Some shops will fill them to 3600 psi where they hold 127 cu ft while other shops will only fill them to 2400 psi regardless of the plus rating and then they only hold 84 cu ft.

So all in all:

An underfilled (3300 psi) X7-100 holds more gas than a worthington LP 95 filled to 2640 psi and it weighs 9 pounds less than the Worthington LP 95.

If you drop down to 3000 psi in the X series tanks, a X7-100 holds 86.7 (stilll more than an LP 95 at 2400 psi), the X8-119 holds 107.2 cu ft and the X8-130 114.5 cu ft.

So whining about underfills is more of a popular whine than a real concern even in the rare instances when it might happen - and in those cases, it is usally a case where everyone's tank get hotfilled to only the service pressure with the result that they all get underfilled by about 200 psi.

 

[H2O 70]

I think it is a non-issue. I haven't found a shop that can't handle HP tanks. Boat compressors may be another issue. As pointed out above, if you have a tank rated for 3442 and end up with 3100, your not loosing that much. Fast fills are the biggest challenge. I've taken an IR thermometer with me to the dive shop to actually show them how warm the tank is. I try to get the shop to fill at a rate they would use for partial pressure blending. I get better fills.

 

[Matt S.]

My LDS has the gear to fill HP tanks and still I always end up with 2800-2900 PSI. I can count the times that I have seen a fill over 3300 on one hand.

My other slightly less convenient tech-oriented LDS always gives good fills.

 

[H2O 70]

My LDS has the gear to fill HP tanks and still I always end up with 2800-2900 PSI. I can count the times that I have seen a fill over 3300 on one hand.

My other slightly less convenient tech-oriented LDS always gives good fills.

I'd pay attention to their fill rate. If they are filling to tanks rate pressure, assume 3442psi, and you're ending up with 2800-2900, something is hot.

I try to keep my tanks in my truck in the AC before they get filled. If they are in the bed of the truck and they get to 115 then I get them filled and they warm up to 125ish. That is only 10degrees or 70psi. Then they end up in the AC and get cooled down to 70degrees, you're talking 55degree difference or 380psi. Hop in cold water and then you're below 3k.

Bring the tanks in cold and nice slow fills. I get the best fills when I get him to fill >5psi/s, or less than 300psi/min. The slower the better. My tanks maybe get 20degrees warmer than what I came in with.

 

[Scott L]

To my dismay I steered 9 cylinder's to be filled in Key Largo over the holidays to a shop I received instruction with and they filled our HP cylinders to 2800-2900psi and 3% points below the mix requested. No time to remedy before our rather expensive spearfish charter set sail. You have to be carefull using unfamilar shops. Luckily, I live close to a refrigerated wet-filling station who's fills will put a major smile on one's face...

 

[Matt S.]

The weird thing is, I have watched them fill my tanks, and felt how warm they get. I didn't have a thermometer with me, but it was reasonable. I think they may have the pressure gauge on their fill station intentionally set short, or something, because I have picked up a tank, had them top it off, and still seen it hundreds of PSI lower later on.

I don't think it is my gear as I have verified it with other SPGs, and I get a proper fill from another shop.

It isn't a big deal normally as I dive 119s and always have a ton of gas left anyway after a typical dive. But it is peculiar.