What Size Doubles?

[stuartv]

I have never considered intentionally going to about say 600psi on my back tank before switching to the pony (now making it a stage bottle) to extend my dive times.

Personally, I would not do that. All my training so far has been that if I carry a pony it's only for emergencies (unless it's a deco gas). In other words, if I carry a pony, I would only ever use it if I (or someone else) really screwed up (or had some really bizarre accident/malfunction).

That said, if I had some really good reason to do a dive where I felt a need to plan up front to use more gas than my back mount tank, I would probably start the dive on back mount. Then switch to the pony as soon as I got to the bottom. Breathe it down to near empty. Then switch back to my nearly-full back mount tank to complete the dive.

But, really, you should be able to get a handle on things where you can do NDL dives to 100' on a full 100 without having to cut your dive short because you're low on gas (and without needing doubles and without using a pony as part of your dive plan). At least, I *think* so.

 

[PfcAJ]

I have never considered intentionally going to about say 600psi on my back tank before switching to the pony (now making it a stage bottle) to extend my dive times.

That's backward and not a good way to use a stage bottle.

 

[Reku]

I love my lp85's - but that's just me.

 

[pinshootr]

might as well look at side mount !!!

 

[Bigeclipse]

might as well look at side mount !!!

I was contemplating that but I am partially set-up for BP/W (I already have the backplate/harness) and also the two agencies/diveshops I have been looking into for technical training do their certifications in back mount only. I am in the NY Albany area and it seems the only technical instructors are located near NJ.

 

[tbone1004]

If I owned 7/8 tanks I would not replace them either. OTOH if I was buying tanks, with plans for building doubles, I'd prefer 3/4 tank necks simply because sourcing manifolds is easier. There are 7/8 manifolds to be had, but they can be a bit of a chase.

If the right deal came along for a pair of 7/8 tanks, and I had a manifold I wouldn't hesitate.

Tobin

the ones I linked were a set of PST120's doubled up for $400 and local to him, so I would consider that the right deal for this situation, but that's just me

 

[CAPTAIN SINBAD]

I wonder why HP-117s are not more popular than HP-100s. They are not longer than HP-100s but they are fatter and do not weigh much more than 100s. If anyone has experience with 117s then I would like to hear your complaints.

 

[Doby45]

That's backward and not a good way to use a stage bottle.

Spoken for truth..

 

[cool_hardware52]

the ones I linked were a set of PST120's doubled up for $400 and local to him, so I would consider that the right deal for this situation, but that's just me

Indeed, that just about the cost of the manifold and bands alone. As you noted there is nothing inherently wrong with 7/8 valves, and an existing built set of doubles has all the requisite parts, and the wear parts for the manifold are generally available. OTOH if some body is looking to piece together a set it's a different story.

Tobin

 

[tbone1004]

preach brother tobin, I thankfully stumbled on some OMS valves for mine, but they are certainly few and far between