Scubapro 156 and 108 first stage advice.

[John C. Ratliff]

Second stage does not influence IP but an unbalanced second IS influenced by IP. When you set the cracking pressure on an unbalanced second you need to do so at a tank pressure where it will see the highest IP (high tank pressure for a piston and low pressure for a diaphragm). If you set your unbalanced second at high pressure, then when the tank pressure drops to 300-500 psi and IP rises on a diaphragm first (even on a balanced first it can go up as much as 10-12 psi) it may cause the second to free-flow (if your second was tuned at the edge of easy breathing). Hope that explains it.

I think that you are referring to a newer design, called an “Over-Balanced First Stage.

Over-Balanced Regulator001 by John Ratliff, on Flickr

Because my understanding of a balanced first stage is that it really does not respond to fluctuations in tank pressure. But the “Over-Balanced First Stage,” by Aqualung, actually built in an increase of the IP as the diver descends, according at least to this advertisement.

The original balanced first stage was the Calypso, by U.S. Divers Company, and it did not have a fluctuation of the IP with changing tank pressures.

IMG_1824 by John Ratliff, on Flickr

SeaRat

 

[PfcAJ]

I think that you are referring to a newer design, called an “Over-Balanced First Stage.

Over-Balanced Regulator001 by John Ratliff, on Flickr

Because my understanding of a balanced first stage is that it really does not respond to fluctuations in tank pressure. But the “Over-Balanced First Stage,” by Aqualung, actually built in an increase of the IP as the diver descends, according at least to this advertisement.

The original balanced first stage was the Calypso, by U.S. Divers Company, and it did not have a fluctuation of the IP with changing tank pressures.

IMG_1824 by John Ratliff, on Flickr

SeaRat

I think there’s 3 things being discussed.

Balanced (IP independent of tank pressure), overbalanced (IP sees slight increase with increased ambient pressure, independent of tank pressure), and regs that are “balanced” but still see slight variation of IP based on tank pressure. This in contrast to an unbalanced 1st which sees more dramatic changes based on IP.

And of course, all 1st stages put out their IP over the ambient pressure.

 

[Luis H]

Many "balanced" first stages are not perfectly balanced.

Some first stages, like the Conshelf and the Scubapro Mk-5, the IP changes just a few PSI as the tank pressure changes, from full to empty. I think that 5 to 10 PSI change is not uncommon in many of these first stages from my observation, but I have not recorded it. Maybe I will.

Then there are some of the Poseidon "balanced" diaphragm first stages that the IP would have a large change as a function of tank pressure change. Their second stages were not affected by the IP change so I am guessing, Poseidon didn't care. Their newest first stage is supposed to be much better in every aspect.

 

[p_kos]

I think there’s 3 things being discussed.

Balanced (IP independent of tank pressure), overbalanced (IP sees slight increase with increased ambient pressure, independent of tank pressure), and regs that are “balanced” but still see slight variation of IP based on tank pressure. This in contrast to an unbalanced 1st which sees more dramatic changes based on IP.

And of course, all 1st stages put out their IP over the ambient pressure.

Yes, I was referring to “balanced” regs which actually have a small change in IP across tank pressure.

 

[Tr4lover]

Well I was able to use my 156 in the in-laws pool!

 

[lexvil]

Well I was able to use my 156 in the in-laws pool!

That’s the side to side clutch mount

 

[rx7diver]

Well I was able to use my 156 in the in-laws pool!

Um, you can probably pick up an old-school blow-molded plastic backpack w/ harness at your local Play-It-Again-Sports store, for $10 - $15.

rx7diver

 

[Tr4lover]

My other

Well I was able to use my 156 in the in-laws

Added another 109. Addiction is starting to become a problem.

Well I was able to use my 156 in the in-laws pool!

 

[scrane]

My other

Added another 109. Addiction is starting to become a problem.

Time to get tangled up in the ScubaPro D series.

 

[Tr4lover]

Time to get tangled up in the ScubaPro D series.

I really like the new D420. I would like to grab one 2nd hand.