Northwest Dive Club

CaptnJack wrote: generally in a splatter pattern on the bottoms.

That's been my experience. No longer filling at a shop with a water bath, no more tumbles. But, I'm also diligent now to purge the valve.

fmerkel wrote:

CaptnJack wrote: generally in a splatter pattern on the bottoms.

That's been my experience. No longer filling at a shop with a water bath, no more tumbles. But, I'm also diligent now to purge the valve.

My LDS doesn't use a water bath and has two articles post on the wall that support the practice of dry filling. He has also taught me the thumb over opening pressure purge to try and be sure not to blow water / debris into tanks when filling. His other mantra is that slower filling is better filling. The slower the fill rate the less heat generated. Wasn't it the master on Kung Fu that always told Grasshopper to have patience?

Mateo1147 wrote:My LDS doesn't use a water bath and has two articles post on the wall that support the practice of dry filling. He has also taught me the thumb over opening pressure purge to try and be sure not to blow water / debris into tanks when filling.

Be extremely careful putting any body part close to a high pressure gas outlet (fill whip or a tank). You can actually blow gas hard enough on your skin to force air into/under your skin and essentially give yourself an embolism this way. Although its obviously less life threatening than a venous or arterial embolism. Ditto foreign objects like a little sliver of brass from the threads on a DIN valve, or sand etc.

Mateo1147 wrote:The slower the fill rate the less heat generated. Wasn't it the master on Kung Fu that always told Grasshopper to have patience?

Not exactly. There's the same amount of heat of compression going to 500 to 3000 psi in 3 minutes vs. 20 mins (in joules or whatever unit you want to measure in). That heat just has more time to dissipate during the 20 min fill so that at the end of your fill time the gas isn't as hot. Hence the lower pressure drop upon cooling from the slow fill. Same total heat generated just more heat was lost in the extra 17mins of fill time.

I fill 2 HP100's or 120's at a time with my toy 1.9cfm compressor. Takes over an hour, I run them to 3700 or so and still need to come back and top them off when they cool. I have a double barreled mortar sitting here but have never filled it with water and used it. I'll be trying that and report.

If I fill bank bottles or 4 AL80s at a time they don't cool down more than ~200 psi. HP fills from empty cool down about 400 psi no matter what I do, that gas is just much hotter and steel is a poor conductor of heat compared to aluminum.

CaptnJack wrote: This is much different than a steel tube set in the floor. The mesh baskets distribute the force of a rupture in many directions.

Oh ... OK . Now I understand the mortar reference. (It's tough getting old )

Yeah, a pop can set into the floor would be almost as dangerous as not having one at all. Especially since the fill station operator would most likely be occasionally standing directly in the blast zone. In the fire department fill box above, you have to close the door to fill and the pop can has a blast floor and ceiling inside to prevent shrapnel escape but lots of escape paths for the air.

For water bath, you really need to use a water cooling system for it, like my tig welder uses to water cool the torch, otherwise the water just warms up, and says warm.

rcontrera wrote:

CaptnJack wrote: This is much different than a steel tube set in the floor. The mesh baskets distribute the force of a rupture in many directions.

Oh ... OK . Now I understand the mortar reference. (It's tough getting old )

Yeah, a pop can set into the floor would be almost as dangerous as not having one at all. Especially since the fill station operator would most likely be occasionally standing directly in the blast zone. In the fire department fill box above, you have to close the door to fill and the pop can has a blast floor and ceiling inside to prevent shrapnel escape but lots of escape paths for the air.

As long as you don't stand over them, they'll just blow off the roof. What could go wrong eh?

Mateo1147 wrote:The slower the fill rate the less heat generated. Wasn't it the master on Kung Fu that always told Grasshopper to have patience?

[/quote]Not exactly. There's the same amount of heat of compression going to 500 to 3000 psi in 3 minutes vs. 20 mins (in joules or whatever unit you want to measure in). That heat just has more time to dissipate during the 20 min fill so that at the end of your fill time the gas isn't as hot. Hence the lower pressure drop upon cooling from the slow fill. Same total heat generated just more heat was lost in the extra 17mins of fill time.[/quote]


You are most correct. Same heat generated regardless of time but the fact that it has a chance to dissipate during the fill reduces the need to top off or overfill IMHO. The lower the gas or cylinder temp at the end of the fill the less pressure loss due to cooling after the fill whip is removed.

Put my tanks in a bath, pump them up to 4,000 psi and I have a 15 minute fill with nearly 3500 psi when I hit the water! And that's all I have to say about this!

My dive shop fills them from the bank, dunks them in the water for a while and then tops them off dry again. I don't think that at the temperatures involved that thermal cycling is an issue for steel but I wouldn't want them to do it with an aluminum tank because of its much higher thermal conductivity (although offset by higher specific heat) and lack of fatigue limit.