Skills For Carrying And Using A Pony
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The Chairman
Chairman of the Board
So, two ponies.Pete,
I'd sure be up with diving with you, but I might be in sidemount, so no pony!
FWIW, I often dive an AL80 stage and an AL 40 deco (%100) with my two LP112s. But not in the ocean. I usually dive back mount in the ocean and after Wed, will be diving a rebreather with a bailout. Class starts on Monday! Yay!
CuzzA
Wetwork for Hire
After hearing a number of stories on here about DM's closing tank valves, last year I went ahead and put vindicator knobs on all my tanks. Of course I still do my pre plunge breathe/SPG check, but I figured for how cheap they are, it was worth it in the event someone decided they were going to mess with my tanks and I had a brain lapse or fell off the boat or something. Hopefully the guy will see the knob thread is turning red as he closes off my life support... maybe not. :/
dumpsterDiver
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Red / green color blindness... Keep that in mind...
CuzzA
Wetwork for Hire
And I'd be one unlucky diver. It actually amazes me that a DM would close someone's tank without at least notifying the operator he touched the valve. I was somewhat shocked to read so many accounts of this.
claymore
Contributor
It has happened that DM's/others have gotten confused with the 1/4-1/2 turn back from full open and turned the valve full off or a 1/4 to 1/2 turn on. At the surface you may not be able to see a drop in pressure when breathing but at 30 feet or more there is not enough gas passing though the 1st stage valve. The turn back teaching is based on technology and usage that is not relevant with scuba usage and today's valves.
I am no expert on valves, but my course director explained to me, that in order to be opened fully, you need to have what is called a "back seated" valve, which scuba valves are not. My understanding (and I am not fully confident in writing this, but just wish to open up the conversation for those with a background in mechanical engineering) is that water will seep in slowly when opened "too far", shortening the valve's life. However, when tec diving, the importance of turning off a valve in the case of a free flow situation trumps the lifespan of the valve. Yet, I would almost argue, that with all the screw ups that happen, the valve should be fully on. I know that when I am on vacation and boat dive, I do turn the valve on completely.
My 19 cu ft pony bottle will make me roll to the right when I'm perfectly still.[/QUOTE]
This is a common complaint for divers who chose to carry pony bottles or small sling tanks. I always attach my pony bottle to the left side of my BCD to allow me direct access to my alt second stage should I or my buddy need it. Therefore I'd recommend shifting your weight distribution over to the opposite side to counterbalance the weight of the pony/sling tank. I also find this more comfortable with intregrated weight systems.
OP
2airishuman
Contributor
I've had a dozen different cylinder valves apart from representative manufacturers, from the early 1960s through now, and I think this is urban legend.
Every valve I've seen is designed the same way, with some slight variation in component sizes, outlet port configuration, type of bonnet seal, and type of packing. The bonnet seals can either by an O-ring or a copper crush washer, the only meaningful difference being that the crush washer requires greater assembly torque. All use a non-rising stem design with spring to keep the packing compressed between the core and the bonnet. Some use two teflon rings for packing, and some use a teflon ring and an O-ring.
In either case, because of the spring, the valve stem will seal whether or not the valve is all the way open. The O-ring packing will tend to seal more securely with increased gas pressure because, as is typical with O-ring seals, the pressure pushes the seal more tightly against the stem and housing. If the valve is turned all the way open, there's additional pressure against the packing O-ring or teflon washer, as the case may be, and as long as excessive force isn't used, there's no harm and no leak.
Changes in operating temperature can lead to thermal expansion and contraction of the valve assembly, so a valve that is opened all the way might tighten up with a substantial drop in temperature. With the elasticity of the O-ring I think it's farfetched to believe this could lead to damage or jamming.
I open the valve all the way.
The Chairman
Chairman of the Board
While not all valves are built the same way, most scuba valves are pretty close. I've seen plenty of back seated valves, but never on a Scuba tank.
I charge my stages and then turn them off until I need them. I have enough to worry about than to keep checking my stage to see if it's got a slight free flow. Also, should I accidentally breathe off the stage accidentally, the lack of air in a breath or two should tell me I'm being a doofus. However, I don't want water finding it's way into the valve and hose, so pressurizing it first only makes sense.
When I turn my valves on, I open them fully and back off a third of a turn or so. A loose valve is an open valve. A set valve is a closed valve. I saw a diver twist off the handle of their valve once thinking it was closed when it was all the way open. It was actually very funny to watch (sorry, Brian) and was the first time I got to see the inside of a Scuba tank valve. Some people in the cave community frown on this due to possible roll offs. A valve that's fully seated backwards may not move if bumped against the ceiling. The easy solution is to stop bumping your tanks off of the ceiling! If you do bump, reach back and make sure everything is open (especially the left post). It's never happened to me. Now that I side mount in a cave, I really don't have to worry about this at all.
I charge my stages and then turn them off until I need them. I have enough to worry about than to keep checking my stage to see if it's got a slight free flow. Also, should I accidentally breathe off the stage accidentally, the lack of air in a breath or two should tell me I'm being a doofus. However, I don't want water finding it's way into the valve and hose, so pressurizing it first only makes sense.
When I turn my valves on, I open them fully and back off a third of a turn or so. A loose valve is an open valve. A set valve is a closed valve. I saw a diver twist off the handle of their valve once thinking it was closed when it was all the way open. It was actually very funny to watch (sorry, Brian) and was the first time I got to see the inside of a Scuba tank valve. Some people in the cave community frown on this due to possible roll offs. A valve that's fully seated backwards may not move if bumped against the ceiling. The easy solution is to stop bumping your tanks off of the ceiling! If you do bump, reach back and make sure everything is open (especially the left post). It's never happened to me. Now that I side mount in a cave, I really don't have to worry about this at all.
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