Pony bottle pressure gauge?

[tomboyy]

If this is truly a "pony" bottle and not a deco bottle or an extra tank to extend your dive then all you really need is a small gauge to check that the tank is full. You don't need a gauge, you can use a tank checker. As the pony or buddy bottle is for bailout only, once you are in a bailout situation you are going up no matter what and when you run out of air, you are out of air, if that is in the deco or safety stop, oh well, should have had a larger bottle. A gauge changes nothing--you are going up and you either have enough air or you don't. You will know you are out of air when nothing comes out of the regulator, from there on you are doing a free ascent. N

N is right... for your pony you only need to know it's full when you begin your dive. I paid like 20-30 dollars for mine and only check it when I first hook it up.

 

[redacted]

I have a 2" SPG on the regulator I use for a sling mount tank. I may sling an S63 in which case the SPG is absolutely necessary as that tank is both part of my primary gas plan and my reserve. I also use the reg on an S13 as a pony which is a bit marginal on gas when diving to 100ft. I use the SPG to help execute my ascent as I may use most or all that gas. I plan to hit the 15" rest stop with at least 500 psi, so that means hitting the 30ft stop with at least 900 psi. Without the SPG, I would not be able to do as slow an ascent as I would prefer.

 

[DaleC]

I'm curious about a couple of statements so far. SPG/no SPG?
To my mind a button SPG is still a SPG, just a less precise form.

Considering how much we spend on gear and all the time we are supposed to be spending training and practicing safety drills etc... I don't know why anyone would dive a blind tank to save $25.

But I guess I was wrong about most people thinking you should have one, just most people I dive with.

 

[redacted]

I'm curious about a couple of statements so far. SPG/no SPG?
To my mind a button SPG is still a SPG, just a less precise form.

Considering how much we spend on gear and all the time we are supposed to be spending training and practicing safety drills etc... I don't know why anyone would dive a blind tank to save $25.

But I guess I was wrong about most people thinking you should have one, just most people I dive with.

If your pony is generously sized and full at the beginning of a dive, then the SPG is unnecessary as long as you only use the pony for an emergency ascent.

Button SPGs are not only smaller with lower resolution (precision), and perhaps lower accuracy, they also tend be lower quality. I tried one and it was a leaker.

 

[Scared Silly]

Three terms, rarely used properly -

Accurate - is the reading correct?
Precision - is the reading repeatable?
Resolution - what is the smallest reading possible?

 

[Dive Junky]

I'm curious about a couple of statements so far. SPG/no SPG?
To my mind a button SPG is still a SPG, just a less precise form.

Considering how much we spend on gear and all the time we are supposed to be spending training and practicing safety drills etc... I don't know why anyone would dive a blind tank to save $25.

But I guess I was wrong about most people thinking you should have one, just most people I dive with.

As mentioned if it is just a reserve air supply to only be used in an emergency there is no need to moniter it. If you run out of air you switch over and make an immediate ascent. The only time you need to check it is at the surface before the dive begins. Having an extra hose and gauge only increases your chance of snagging it on something and gives you an additional failure point. However that being said, I use mine only as a reserve but still like the gauge. If I do need it I wanna know how much gas is there so I can regulate my rate of ascent.

 

[DA Aquamaster]

Three terms, rarely used properly -

Accurate - is the reading correct?
Precision - is the reading repeatable?
Resolution - what is the smallest reading possible?

Even if properly used, they are still problematic.

Under good light, high contrast and ideal conditions, (for example a well designed target rifle sight) the human eye can detect differences as small as 1/5000 of an inch. So resolution is dependent on the environment and individual as well as the gauge itself.

Repeatability is nice but means little if resolution is poor and is meaningless if accuracy is poor.

Accuracy is also not as black and white as it sounds and what is an acceptable level of accuracy depends on the application. For example the local Dominos number is 90% accurate - (703) 521-3031 - but dialing it will not get you even 10% of a pizza. I am not sure who will answer.

In terms of SPGs many people insist on 100 psi increments, even though the human eye can interpolate to a resolution of 100 psi on the better 1" button gauges.

The irony of course is that many of those same people are happy as clams with 100 psi increments on a large SPG that may have a 100 psi error in the middle of the scale and 200 ro 300 psi at one end or the other - making the 100 psi resolution meaningless, even if it is also repeatable as it is not accurate enough to take advantage of the 100 psi increments.

And of course, for a pony bottle a gauge with a big fat needle and broad ranges of full/partly full/empty across a range of 3000 to 0 psi would be more than enough in terms of accuracy, precision and resolution.

 

[DA Aquamaster]

I would also recommend trying it out occasionally. On my last dive of the weekend I will sometimes test myself, switching over to the pony and doing my ascent on that (last dive because it would mess up my air-integrated computer tracking for any subsequent dives). Having done that several times, I know I can ascend from at least 100' with my normal safety stops on my 19cf tank - and that's still with plenty of air left.

More people should do this on a regular basis. It is a real confidence builder to know that your piny can get you up from the max depth you dive as well as to know you can do it with a normal ascent rate and a safety stop.

Plus, as you progess throught the season pressurizing and depresurizing the reg on each dive, the tank loses pressure and volume, so you need to top it off to keep the same level of reserve gas - and if you hav to top it off, you just as well practice with it on the last dive of the day now and then and make the fill a good one.

 

[DaleC]

I understand the all or nothing aspect of pony use and that there is a risk of mechanical failure but my concern is the greater risk of human failure. By eliminating a mechanical failure point one is adding a human failure point to the system.

At some point one has to measure the volume of gas in the tank. If you have a SPG on the first stage (whether it is a button or not) you are guarenteed to check it every dive (if you bother to look).
If you don't have one on the first stage of your pony reg set you are forced to attach a device (main reg set or tank checker), read the pressure, disconnect the device and then attach the pony first stage.

Human nature being what it is, at some point this may begin to seem a little onerous and at some point a diver might for go checking the pressure (just this once). "After all, I didn't use it last time so it should still be full". Just this once becomes a habit and one day at a hundred feet they need the pony and...
Of course none of us would ever do that but somehow people still do manage to jump in with their main tank valves closed, drysuit hoses disconnected, no weights in their pockets etc...

I understand that, in a minimalist sense, one isn't "needed" but for the cost I can't see why one would not want to be able to easily read what was in the tank at any point in the dive.

I'm not critisizing anyones diving habits BTW, just providing the counterpoint argument. Everybody needs to make up their own mind as to what is neccisary for their personal safety.
Dale.

 

[Dive Junky]

I understand the all or nothing aspect of pony use and that there is a risk of mechanical failure but my concern is the greater risk of human failure. By eliminating a mechanical failure point one is adding a human failure point to the system.

At some point one has to measure the volume of gas in the tank. If you have a SPG on the first stage (whether it is a button or not) you are guarenteed to check it every dive (if you bother to look).
If you don't have one on the first stage of your pony reg set you are forced to attach a device (main reg set or tank checker), read the pressure, disconnect the device and then attach the pony first stage.

Human nature being what it is, at some point this may begin to seem a little onerous and at some point a diver might for go checking the pressure (just this once). "After all, I didn't use it last time so it should still be full". Just this once becomes a habit and one day at a hundred feet they need the pony and...
Of course none of us would ever do that but somehow people still do manage to jump in with their main tank valves closed, drysuit hoses disconnected, no weights in their pockets etc...

I understand that, in a minimalist sense, one isn't "needed" but for the cost I can't see why one would not want to be able to easily read what was in the tank at any point in the dive.

I'm not critisizing anyones diving habits BTW, just providing the counterpoint argument. Everybody needs to make up their own mind as to what is neccisary for their personal safety.
Dale.

I agree with all of the above. I have seen divers not even check the air in their rental pony. You remind them and all they say is 'oops i forgot'. ?????? Having the gauge on there definately makes it easy to check the pressure. I guess the gauge you use is dependant on the individual but, it is a good idea to have one on there.