Filling Doubles Is Easy

[@williamsweet7511]

love the technical stuff, behind the scene scuba stuff is cool. Thanks for your channel been watching for years.

[@LakeHickoryScuba]

Glad you liked the video William Sweet. We have been discussing making a series of behind the scenes operations of the scuba industry. We have videos produced and scheduled until the end of April, so we may start producing some after that on the Scuba Industry as a whole and what goes on behind the scenes at dive shops.

[@mikkosport2300]

It is quite handy to put pressure gauge (or 1st stage with spg ) to the ther post while filling. Then you'll see the actual tank pressure and can be sure the manifold is, indeed, open. Once friend of mine who was not experienced double filler, closed the manifold during fill. When I opened the valves while ktting up it was an unpleasant surprise: My SPG showed only 120 bar instead of 200. That dive was quite short. Fortunately it eas a rec dive anuway.

[@LakeHickoryScuba]

You make a great point Mikko Sport. I’ve had that happen to me on trips before. The fill operator did not confirm that the manifold was open, and when I did my pre dive safety check my pressure dropped immediately. Needless to say I wasn’t happy with him, when he tried to charge me for another fill. I train all my fill operators to always verify the isolator is open. They have a check list next to the control panel that they read through for every fill. External Inspection, Hydro, Vis, proper adapter, proper gas source, all valves open that has to be open. So far, we have never had a customer tell us we gave them a bad fill.

[@nefarious_kitty]

If you're filling with the same mix that is already in the doubles, then just using one post is fine. However, in my experience, if you're trying to achieve a different target mix (e.g. 25% O2 at 2600 psi) than what is present in the doubles (e.g. 32% O2 at 1000 psi), you're more likely to achieve the target mix in both cylinders by filling on both valves at the same time. Yes, both cylinders *eventually* reach the target mix if you did the math correctly, but since the flow from valve into the attached cylinder is not the same as the flow from the valve into the manifold to the other cylinder, neither cylinder will have quite the right mix immediately after you finish filling.

[@LakeHickoryScuba]

Hello Chris Grimes, that is very interesting. Thankfully, we have never had that issue, but it definitely raises some concerns. We routinely will blend Nitrox from Nitrox, basically adding a lower or richer blend to a current mix, and have never had an issue with it not being the same as what the customer wanted. This being said, I have notice over my career that steel tanks due to how hot they get, the mix can change if I am filling via partial pressure blending. As we all know, Charle's Law, can and does effect blends, as temperature rises and falls, pressure goes with it. This can cause one blend to change as the cylinder cools. Since we fill via constant flow (ie. Nitrox Stick), we have never had this issue.

[@timreynolds9430]

Why did you control the fill from the cascade bottle vs the fill panel to the left? Thanks.

[@LakeHickoryScuba]

Great question Tim Reynolds. With our system, you can do it either way. When filling from the control panel, the cascade bottle must be all the way open. It takes about 20 complete turns to open it fully. If I open the control panel knob, it’s a simple quarter turn. Then to control the flow rate, I just barely crack the cascade bottle. It’s just a more simplistic way of doing it. Several of our other fill operators prefer the other way. We are planning on adding several more fill whips to the control panel, so if we open all of them up and equalize the bottles together, then all we have to do is cascade up by simply cracking the cascade bottles one at a time. This prevents the 20 turns for each bottle.

[@timreynolds9430]

@LakeHickoryScuba That makes a lot of sense. Thanks for the reply.

[@bugbear323]

Where are the SSI Nitrox class? Where are the Good, bad and Grate Dive spots in WNC?

[@LakeHickoryScuba]

Hello Bug Bear, any SSI Training facility can teach you the SSI Nitrox Course. In regards to some great dive spots near or in the western side of North Carolina, some of my favorites are the PDRA Quarries, Grey Quarry (in Tennessee), Lake James, Lake Hickory, and Lake Norman. Most of our lakes if not all, are manmade. There are still plenty of sunken structures to dive on, including Houses and Graveyards. Another great place is Lake Phoenix which is in Rawlings Virginia.

[@391wombat]

Don’t both tank valves have to be open?

[@LakeHickoryScuba]

Hello 391wombat, great question. The valve knob only operates a seat that allows air to exit the orifice of the valve. The air can move freely through the manifold as long as the isolator is in the open position. This is what keeps the cylinders equalized. Thus, only one cylinder needs to be opened to fill both.

[@HKChad]

If you opened the valve that didn't have anything attached all the air would blow out of the valve. This is why doubles are good in the event you blow a 1st stage, you can still access all the gas in both tanks, you just shut off the post that is bad and breath off the other side.

[@391wombat]

Im not a doubles diver so never knew that! Good to know though! Thank you both of you.

[@blackoceandiving8242]

Doesn’t carrying the doubles by the manifold cause extra strain on the manifold? I carry mine by both tank valves with both hands. I’ve heard that you don’t carry doubles by the manifold. Is that some sort of a myth?

[@LakeHickoryScuba]

Hello Black Ocean Diving, that is most definitely not a myth. Putting any stress on the manifold can cause stress to it, which could lead to the failure of an O-ring, or warping of the brass. In this case however, the short distance these cylinders were moved, was minuscule at best, and the integrity of the system was in no case compromised. Great question though. Another thing to remember, is the weight distribution of these cylinders. These small 80’s are very light, and the amount of force it would take to damage the manifold at that distance is negligible.