Tusa 790 hard to breathe below 50'

[KentB]

I have a Tusa 790 reg setup

tusa 700 first stage
tusa s90 primary
tusa s60 octo

I bought it feb 2016 it worked well until feb 2017 in which case it got noticeably harder to breathe below 50' I took it to shop I bought it from for annual service. voila it worked like a charm 10-11 dives and 2 months later last weekend it did the same thing at 55' it was hard to breath switched to octo it was fine.... switched back and went up to 45' and it was fine dropped down to 55 and it was hard again. I got my dive buddy to try both as well to make sure Im not going crazy and he agreed with me.
I called the shop and they said bring it back and we will give you a loaner reg while we get to the bottom of this. which was cool.
the shop is being more than helpful and are going to deal with it but Im more curious why a balanced first and second stage regulator would do this?

I dont think it was anything the shop did when they serviced it as this last sunday when it started acting up was the most shallow of the 10-11 dives since the service, all the dives were between 90-110 ft and it worked like a charm.

any ideas??? this is more for my own curiousity than anything

 

[halocline]

I would guess, and it's really just a guess, that something is sticking in the lever or poppet of the s90. There's no real reason why it should be any different at 55' from 45'. 2nd stages don't really work any differently with depth changes until you get so deep (way beyond recreational) that the gas viscosity changes enough to cause significant line friction. Its the 1st stage that must flow more gas to supply the higher IP as depth increases.

But if your s60 worked fine off the same 1st stage that eliminates the 1st stage as a problem, and the fact that it works fine for several dives and then suddenly acts up, it's likely to be some moving part that's getting hung up.

I looked, the s90 is sort-of a G200B looking 2nd stage with what seems to be almost identical barrel poppet components. It's probably a pretty good performing reg. The s60 looks like a R380 or something like that, downstream unbalanced.

One other thing, sorry for the shameless plug. A friend and I bought a large package of assorted NOS scubapro parts, and in the package was a bag of TUSA parts. I'm interested in finding someone who might have good use for those.

 

[Fishpie]

Yes, probably something sticking in the primary 2nd stage. Could be lever, spring or dried lube in balance chamber.
The TUSA looks to be identical to a Scubapro Mk17 S555.

 

[buddhasummer]

I would guess, and it's really just a guess, that something is sticking in the lever or poppet of the s90. There's no real reason why it should be any different at 55' from 45'. 2nd stages don't really work any differently with depth changes until you get so deep (way beyond recreational) that the gas viscosity changes enough to cause significant line friction. Its the 1st stage that must flow more gas to supply the higher IP as depth increases.

But if your s60 worked fine off the same 1st stage that eliminates the 1st stage as a problem, and the fact that it works fine for several dives and then suddenly acts up, it's likely to be some moving part that's getting hung up.

I looked, the s90 is sort-of a G200B looking 2nd stage with what seems to be almost identical barrel poppet components. It's probably a pretty good performing reg. The s60 looks like a R380 or something like that, downstream unbalanced.

One other thing, sorry for the shameless plug. A friend and I bought a large package of assorted NOS scubapro parts, and in the package was a bag of TUSA parts. I'm interested in finding someone who might have good use for those.

Tusa, not surprisingly, has a pretty big showing here, if you have no joy moving them perhaps I could try on our auction site.

 

[KentB]

I would guess, and it's really just a guess, that something is sticking in the lever or poppet of the s90. There's no real reason why it should be any different at 55' from 45'. 2nd stages don't really work any differently with depth changes until you get so deep (way beyond recreational) that the gas viscosity changes enough to cause significant line friction. Its the 1st stage that must flow more gas to supply the higher IP as depth increases.
that was my thoughts as well, but Ive never taken one apart.

But if your s60 worked fine off the same 1st stage that eliminates the 1st stage as a problem, and the fact that it works fine for several dives and then suddenly acts up, it's likely to be some moving part that's getting hung up.
exactly

I looked, the s90 is sort-of a G200B looking 2nd stage with what seems to be almost identical barrel poppet components. It's probably a pretty good performing reg. The s60 looks like a R380 or something like that, downstream unbalanced.
I was told it was ment to be a pretty good regulator for cold water diving

One other thing, sorry for the shameless plug. A friend and I bought a large package of assorted NOS scubapro parts, and in the package was a bag of TUSA parts. I'm interested in finding someone who might have good use for those.

sorry annual service includes parts

 

[KentB]

Tusa, not surprisingly, has a pretty big showing here, if you have no joy moving them perhaps I could try on our auction site.

what does this mean? tusa regs are no good?

 

[buddhasummer]

No, not at all, Tusa make some very nice regs, in fact have manufactured regs for SP if I'm not mistaken and they have an equivalent/same(?) MK17/Mk11 and I'm sure others. In the US Tusa is not a big brand but here in Japan it is.

 

[halocline]

The TUSA looks to be identical to a Scubapro Mk17 S555.

I had hoped that the TUSA regs were exact copies of the corresponding SP models, but at least with the bag of TUSA parts I have it looks like the designs are very similar but the parts are not interchangeable. This is mostly referring to the 1st stage springs and pistons. Looking at the S555 schematic it sure does look like this TUSA 2nd stage is the same. I wonder if those parts are interchangeable. If so I think I have diaphragms, an air barrel, and some levers.

 

[KentB]

No, not at all, Tusa make some very nice regs, in fact have manufactured regs for SP if I'm not mistaken and they have an equivalent/same(?) MK17/Mk11 and I'm sure others. In the US Tusa is not a big brand but here in Japan it is.

I wasnt sure wha you meant, If you meant a big showing in the " why doesnt this work" section indicating they are poor quality lol