Mailing List Archive Mailing List Archive
Part of this is excerpted from some info I made up for someone off this
list asking about solo diving. Thought it might be of interest in this
thread .
Pony bottles :
For the solo diver the pony bottle really only serves as the wrong
place to put a back-up regulator and imposes an irrevocable
partitioning of your gas supply. A case of attempted back-up by
simple redundancy that actually amounts to a system of independent
singles too grossly mismatched to be managed as back-ups for each
other. A poor back-up system in the final analysis compared to what
else is available that provides for less drag, better reliability, and,
usually, access to a greater supply of gas.
The pony tank was more easily justified in the old days before SPG's
to reduce the risks of running out of gas and has stayed with us as a
cool looking option often used by guys who can't keep track of their
status. How disappointing it is for the cool diver to find that those he
intends to attract and impress see this thing as a "cute little tank"
instead of the neat-o technical device he thinks of it as being.
Actually I think women do this just to hurt our feeling. We only have
one feeling, right ?
The only situation where a pony bottle (completely independent gas
supply system) is a better option over the Y valve on a bigger single
tank for the solo diver is if you blow the tank to valve O'ring or a burst
disc so that you loose everything in your primary supply - not
impossible, but with decent maintenance, highly unlikely, and any time
you are in a situation where you would not still be able to make a
safely controlled ascent in such a case (a couple of final breaths as
the tank drains during ascent and no need for decompression - or
have a partner) should find you with isolatable manifolded doubles on
your back.
One reason the Y valve is more reliable from the standpoint of the
system as a whole is that the pressure on the only two failure points
that the Y valve does not cover (Oring & burst disk) is dropping as the
dive progresses so that the odds of them blowing is much lower by the
time you reach the point in the dive where a fast ascent becomes
appreciably dangerous. The odds, small as they are, of these blowing
in the pony tank will be higher till it is breathed down and, ironically,
this potential failure is the only reasonable one that can justify
partitioning of your gas into two totally independent supplies. Diving
with a fear of running out of gas is not reasonable.
I've never seen it happen but I'm sure loss of gas through a bad or
extruded O'ring is not fast enough to prevent a reasonably safe ascent
from recreational exposures and might even allow a safety stop. The
burst disk on the Y valve can be modified in two ways to reduce the
risk if it�s blowing - higher rating or plugging. I can�t suggest
plugging
because it may be against the law even for a private owner but a
higher rating should still provide the intended protection in fires since
the disk will melt and weaken no matter what the rating.
If you need a back up regulator get an H or Y valve. If you need
more gas get a bigger tank. If you need both, or more gas than a
single can hold, plus more versatile emergency management because
of dependency on functioning equipment for escape then get a set of
doubles with an isolation manifold and learn how to use them.
The real beauty of the isolation manifolded doubles is not the
volume of gas available for the dive but the ability to easily manage
what you have for a true and reliable back up system in any
reasonable scenario (you are usually diving only to 3rds anyway).
You don't have to use big heavy tanks for this, a pair of 50's or 63's
would provide a lot more gas than a single 80 along with the best
back-up capability presently available for open circuit (if you know how
to use it).
This small set of twins is a reasonable option for dives to the limit of
the accepted recreational range - but remember that a set of doubles
does not qualify you for technical exposures.
The one place the pony tank shines is when diving with a partner or
group where the ability to hand it off is a useful advantage. This is a
good option for a divemaster leading a group to have since he would
not be tied up buddy breathing with a single diver when he needs to
remain in a position to lead or manage the rest of the group at all
times.
Yes, this diver should have a partner to buddy breath with anyway
but why not reduce the potential for problems it presents by preserving
this divers independence long enough to get the group organized for
an ascent (or whatever you decide to do). You don't want two divers
preoccupied with sharing gas or pressured to get to the surface quickly
when you are trying to communicate with everyone and stay organized
as a group.
This pony tank should have a clip that allows it to be easily attached
to AND REMOVED FROM the receiver without having to hold it. The
hose should be long enough to allow comfortable head movement and
I like the idea of being able to wrap it around the neck.
This is a scenario that would normally be played out among
recreational divers and once implemented the dive is over anyway so
that there is no need to try to rig this pony as a typical stage would be
for a tech diver.
Keep it simple, easily manageable by the unfamiliar, and comfortable.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Review
A pony bottle does not allow you to get into that part of your supply
unwittingly so that it actually functions much like the old J valve by
warning you of low gas supplies. Useful if you tend to run out of gas
by surprise, in which case you should certainly not be diving solo or
deep. If you have a partner and are following Rule #1 why do you
need a pony bottle when he is functioning as your spare air bearer ?
The H or Y valve and the manifolded twins allow you to breath all your
gas out with no warning so that if you are not monitoring your status
(supply) you are no better off than with a single 80 with a K valve.
Much worse if you stayed long and deep enough to need
decompression stops.
The pony bottle and the isolation manifolded twins cover the
catastrophic loss of gas by burst disc or O'ring failure where the Y or H
valve does not. But the odds of this failure become greater in the pony
than the primary tank by the time one would need it for a safe ascent.
A pony bottle can be handed off to another diver in an emergency
making management of the situation easier and safer in many cases.
It also allows a diver responsible for a group to provide gas to an out
of air diver and still retain the ability to manage the group.
A pony bottle is easy to take on a trip, but a Y valve is even easier -
just put it on the tank you'll be using for the week. (I bought a
complete isolated manifold and bands to make twins out of 80's or
63's wherever I go).
As a back-up for a failed primary regulator a pony actually forces you
to shift to a lesser supply. So what you actually have done is turned
what would have only been a failed regulator into a reduced gas
supply as well, and paid for the privilege by dragging the weight and
resistance of the pony tank around to boot. If you use a pony tank
large enough to negate this factor you may as well make it doubles !
The H or Y valves provide access to the complete supply of primary
gas in the case of regulator failure. (one of the primary reasons not
to dive independent twins)
A Y valve is a little lighter weight and has fewer failure points than
an H valve but faith in the H valve system at this additional potential
failure point is high enough that the manifolds used by the best of the
caving community use it with no qualms expressed. I believe the H
valve is worth the versatility it allows if there is a chance you will use it
to make doubles - otherwise go with the Y valve.
So! WITHIN RECREATIONAL LIMITS, if you feel the need to
compensate for your inability or failure to keep track of your status, a
total loss of primary gas (Oring / burst disk), or to make sharing gas
easier and less restricting in a group situation the pony bottle may be
the best bet. If you only need to back up failed regulators the H or Y
valve is better and I see no logical reason to partition your gas supply.
The only system you should use in any overhead or for
decompression dives is isolation manifolded doubles.
A little philosisifulsizing :
The point of a pony bottle, "Y" valve, or any other such back up
system should not be to "get you to the surface" AND the surface
should not be treated as a place of refuge as far as dive planning
goes. The point of these back up systems is to prevent being "forced"
to the surface by providing a point or situation of refuge below a safe
ceiling - to provide or maintain options that allow you to retain control
of your status - to buy time.
The reason the "spare air" is scoffed at is because it fails to do this -
you are still having to run for the surface though you have a better
chance of making it if you happened to exhale just before you lost
your gas or are choking / coughing due to aspired water.
Often, how you configure, manage, and use a back-up system will
determine whether it is just a bunch of gear that you use to keep you
alive while you run for safety or an efficient system that guards against
loss of control of your status by maintaining or providing options in the
event of foreseeable failures or problems.
Chuck Boone
--
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