First thoughts on new doubles

[David P]

Last friday I picked up my two new Worthington HP 120's and a manifold (already had the HM bands waiting). I did a quick vis on both tanks and put in the modular 300 bar din valves. I then took one of them diving Saturday, well I tried to take them diving but the coast guard gave us the boot as the local Navy base doesn't like us diving in their harbor:huh: So for about 5 minutes or so I was quite pleased with the trim on the 120 over my 119 and am now considering selling off my PST so I can buy another 120 for diving singles... Anyhow so Sunday night I drained both tanks, pulled out my O2 lube (wich thanks to my dogs I now need to buy more, who knew boxers like to eat little tubs of white grease?) and decided to learn how to set up doubles. It wasn't nearly as hard as I expected it to be. It only took me a couple of tries to get both sides of the isolator to start. I got everything bolted together and felt kinda bummed that I had to wait untill Monday to get the tanks filled. So Im sitting there looking at my doubles bolted to my backplate and have my first thought about the set, "Wow thats a lot of money sitting there..." I quickly get over my airless bumming around as I think that I should try them on, lay down on the floor, and see if I can reach the valves. I get the set sholdered on and lay down on the floor, I then have my second thought "Crap these things are heavy! Im going to climb up a lader onto a boat wearing this stuff?" Then my two boxers notice I'm laying on "their" floor and decide that I MUST want to play with them. So now Im laying on the floor with about 100lbs of steel tied to my back, AND two boxer dogs climbing on my trying to lick my face off. I was actually affraid that I was going to have to yell for my wife, wake her up and have her help me get the dogs off of me... But back to the story, so I finally get to make a pool dive with my doubles this evening, I set the rig in to my pool POLITELY as the pool was just replastered and hit the inflator button. Up rises the twins and float quite nicely, I notice that my DR Rec wings are quite full, but hey it floats the two tanks in fresh water so I'll be good to go in the Pacific! I suit up and make a not so giant giant stride into my pool. It seems my bouyancy is slightly more...eradic than it is when I dive singles. Perhaps it is because all the extra weight and the necesarry air to counter act the weight? I am 6'4 with a very large chest and I breath very slowly and deeply so I usually have a slight bouyancy change during breathing but not quite this bad. It is nothing out of control just a little more touchy than I am used to... So I start swimming around a bit, feels different... maybe more stable? It is definelty different than cruzing around in my single. After a while I remembered the valve drills, all I can say is "wow" this is going to take some work. I can reach the isolator no problem (how do most of you have the isolator knob facing, straight up, slightly forward, slightly back?) but the two valves aren't quite as easy. I can grab the valve then walk my hand over to the knob and operate it. I thought the problem was going to be to get my hand to go far enough out to the side to reach the knob, but the problem was to get my hands far enough back past my head. I recently replaced the harness on my back plate and I think I have the sholders a little too tight(and of course trimmed the excess off), it seems to be restricting my arm movement slightly so I think I'll get some more webbing and try again. One way or another I'm pretty sure I will be spending some more time in my pool here in the not too distant future.

 

[Mark Vlahos]

Just a note about the valve drill. The isolator can be tilted slightly toward the back of your head. For me, this makes it just a little easier to reach. To reach the other valves keep your elbow "forward" or "in", don't let your elbow swing out wide, the geometry of your shoulder joint acutally lets your hand get further back when you keep your elbow in close to your ear.

The bouyancy swings are most likely becasue of the rather large air bubble in your wing. Go up just a few feet and it will expand enough to get you going up, descend a few feet and you loose the bouyancy as the size of the bubble decreases. It is the same problem new divers are often forced to deal with when they wear far too much lead, in your doubles you are overweighted. With my double 130's the swing from full to empty is enough to make me feel really heavy at the start of a dive.

Remember, when you lift the doubles lift by the valves, directly over the cylinders. DO NOT lift the doubles by the center of the manifold, you can damage the manifokd this way. You will also now have the problem of making sure that the place where you get fills knows how to move them, and gives you fills with the isolator OPEN. I also have a couple of shirts with tear holes from the bolts, get into the habit of turning the cylinders around if you are going to carry them.

Good luck,

Mark Vlahos

 

[David P]

Thanks for the tip on the elbow, Ill have to try that. I read about lifitng by the manifold and don't want to tempt fate with a blow out. Fortunately I work part time at my lds and we can do fills up to 4500. Its funny though, I was filling them the day after I bolted them together and my boss came over to watch. He was asking about the isolator and how to fill doubles. He said he had only filled one set of doubles before and had some issues. I think I might have him interested in trying diving doubles, now only if I could get him in a back plate...

 

[Mark Vlahos]

Thanks for the tip on the elbow, Ill have to try that. I read about lifitng by the manifold and don't want to tempt fate with a blow out. Fortunately I work part time at my lds and we can do fills up to 4500. Its funny though, I was filling them the day after I bolted them together and my boss came over to watch. He was asking about the isolator and how to fill doubles. He said he had only filled one set of doubles before and had some issues. I think I might have him interested in trying diving doubles, now only if I could get him in a back plate...

If your manager is not very experienced in filling doubles I would suggest that when he does he gets into the habit of treating them like big singles. If he is doing a partial pressure Nitrox fill he should get into the habit of only using ONE post. First, make sure the isolator is open. Second, connect the O2 and fill to the appropriate pressure. Third, connect the AIR fill whip to the same post that was used for the O2 and then top off with air.

While in theory it should work by using O2 on one post and air on the other, if the isolator is closed you might have a dangerous fill. Rick Murchison did a test several months ago to see how well the two gasses mixed in the cylinders. To make a long story short, they did not really mix. Even after waiting for quite a while he had one cylinder with Oxygen and the other cylinder with Air. The method for the test was to fill each cylinder with the isolator closed and then open the isolator and wait for the gasses to mix.

By filling from only one post, even if you forget to open the isolator you will always have the gas the correct mixture, just at less pressure after you open the isolator.

Have fun,

Mark Vlahos