I've been using these tiny SPG's that are built
into a 1/2" nut package that's like 3/4" high.  They screw directly into 
the HP port, are low-profile, with a tiny (but fairly accurate) guage
inside, that clearly shows red at 500PSI, yellow at 1000,
and green above.  I rig the deco bottle so that the SPG "nut"
is pointing up, and it's fairly easy to read.  

And the things are indestructible - I've dropped an AL80 
deco bottle rigged this way where it fell directly on the 
SPG from several feet, and it keeps on going.

For deco bottles, they're perfect, because all I really want is
a ball-park estimate of how much gas is available - I've
already planned for consumption and reserves, so who cares
if I know whether I've got 1500 or 1625 PSI.

They run about $30 apiece at my local high-markup dive shop.

-Will

On Tue, 27 Jan 1998, David Shimell (shimell) wrote:

> 
> Chris
> 
> Thanks for taking the time to reply.
> 
> >Firstly, deco cylinders without gauges will bite your ass one of these
> >days (ask Martin Smith about that one). The arguament of an extra
> >failure point usually rears it's ugly head in discussions like this.
> >From most folks experience, a proper stage regulator set up (gauge not
> >flapping in the wind) is about as reliable as the rest of your stuff.
> 
> I'm not aware of that particular Martin Smith incident.  The procedure I   
> apply works but if I became complacent it would fail, just as if I get   
> complacent about gas planning or any other aspect of my diving.  You will   
> be glad to hear that it is not in my nature to be complacent!  I agree   
> with your point that the likelihood of a short, tidy HP hose failing is   
> low, but my point is that it is avoidable.  HP hoses do fail.  I have had   
> a standard length HP hose blow on the boat as I was about to kit up.   
>  This hose was about 12 months old and on inspection in apparently good   
> condition.  Being anal, I check my hoses every few dives.  I have seen a   
> HP hose go one other time but this was in poor condition and should never   
> have been near the water.  I do not fret about using a HP hose since I   
> use one on my backup regulator on my twinset and I will use a 7" hose on   
> a stage bottle when I need to dive thirds.  I do not use them on my deco   
> bottles as I do not need them therefore I do not take them in the water.
> 
> >If the justification for not having a gauge is substantiated by having a
> >buddy to run to if 'shit happens' (incidentaly, after 20 years of diving
> >and servicing dive gear the only times I have seen a neck O ring fail is
> >down to poor maintenance) then I cannot see any application for a twin
> >set and a 3l 'stage bottle'.
> 
> You are being slightly emotive WRT "buddy to run to", but I agree with   
> your point.  Here we have shifted (I started it!!) from the original   
> discussion of single with pony to twinset with 3l stage.  The application   
> is simply one of using the 3 l cylinder to carry deco gas.  The twinset's   
> redundancy allows more adventurous diving whilst the pony carries the   
> deco gas.  In this instance my gas planning would be such that I can   
> ensure that I can meet my deco obligations with *either* my back gas *or*   
> my 3l deco bottle thus maintaining a redundant configuration and supply.   
>  Since I quite rightly got grief about apparently mis-representing BSAC   
> training - which I hope was due to lack of clarity in my writing rather   
> than my understanding, I will emphasise that the 3l cylinders are being   
> used for entirely different purposes here.  With a single it is used as a   
> bailout from depth and so the contents must be breathable from the   
> maximum planned depth. In the twinset and small deco cylinder scenario,   
> it is just another deco bottle and the "standard" rules of gas planning   
> and management of deco bottles apply.
> 
> I'm starting to get bored with this discussion how about you?
> 
> Dave
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