I like the idea of a button guage. It deffinately makes sense to put a guage on the pony bottle,but having a full sezed one floating around might be a little annoying. Here's another question. Do you guys empty and refill you ponies on any kinf of a schedual? lets say you dive with a pony all the time, but you have never had to use it. would you just keep it full? or empty it and refill it say, once a season if you never have to use it.
George,
First, since you're diving with a bunch of more experienced divers who "know their stuff", what are these experienced guys using for pony bottles?
Second, your question above is a good one. Lots of guys with pony bottles never practice with them. Then when something happens they're over there doing the random freak boogie because they aren't sure whether to crap or go blind.
If you're going to have one to begin with, make an effort to practice with it each dive. Deploy the thing when you start your ascent and come up on it. If its an adequate supply, you'll make it up without incident. If it isn't an adequate supply, better to find out while practicing with it than under real world emergency conditions.
One small point:
In a real world "I may actually die in the next 15 minutes" situation your breathing rate skyrockets, your heart begins pounding, and you start burning through gas like you can't catch your breath. Your respiratory rate and gas consumption may actually double, from something like .6 or .7 cfpm to 1.3 cfpm or higher.
A 20 cu ft bottle that will do nicely for a laid back 60' ascent on a lazy summer afternoon at the lake might leave you sucking dry in a real world crapstorm.
Rather than picking the bottle first, and then finding out how much gas it will hold, you might try a different approach.
Find out how much gas you'd consume per minute during an emergency? (Round up to about 1.5 cubic feet per minute.) Find out how many minutes you may need to be on the bottle (it will be situationally dependent based on how deep/where you dive)? Lets say 100', which is 4 ATA (atmospheres absolute). If you dick around trying to figure out why the world just went to crap at 100' for two minutes, and get your buddy's attention and thumb the dive (one minute), then you decide to head up at a controlled rate of 30 feet per minute (fpm), it will take you ~six minutes total to reach 10'. Suppose you spend a safety stop there for three minutes, then ascend to the surface, which adds another four minutes, for a total of around ten minutes on the bottle. Thats about 15 cubic feet of gas required @ 1.5 cfpm for 10 min. - in which case the bottle you picked would work.
But you can easily see how needing a few more minutes at 100' to unscrew a situation or find your buddy and communicate, (which is why you might need a pony bottle to begin with - the fact that your buddy is not reliable) etc., or having to swim back to an upline before ascending if you're on a charter boat, or needing time to untangle yourself if you're caught in monofilament or a net, etc. can quickly drive your emergency gas requirements above 20 cubic feet.
Take a minute to jot down your worst case scenario, based on where you're located, how you're diving, your buddies input, etc. Lay out your needs. Based on your projected needs, calculate your gas requirements. Then get a bottle to match your needed gas supply. For the moment, if you're going to get a small bottle consider getting a Luxfer aluminum tank in either 19 or 30 cubic feet. (Luxfers offer superior characteristics if you ever want to sling it.) The rest can be worked out depending on what you think will work best for you.
Just FWIW. YMMV.
Doc
