Trieste 2nd stage adjustment

[Gary]

Okay, I'm a little stumped here and maybe one of you could help me out. I finally got the Trieste I've wanted for awhile and brought it to the shop and took it apart to clean it. It didn't have the hoses, the duckbill was dry-rotted and hard as a rock, and the inhalation diaphragm was a bit stiff.
BTW, whoever gave that bit of advise for removing an old duckbill by soaking it in acetone, thank you. This one would have been the toughest to remove if I used my previous methods, instead it was the easiest.
Anyway, back to my story, I cleaned all the parts, replaced the filter, diaphragm, HP seat, LP seat, duckbill, and all O-rings and reassembled it. I adjusted the IP of the first stage to 125 psi and adjusted the locknut of the 2nd stage to just below freeflow. I then put the diaphragm over the lever and clamped the top box on. I then put the hose on the inhalation side and tried to breathe from it.
It was like, to use an old phrase,"sucking a golf ball through a garden hose". I tried readjusting the lever height of the 2nd stage, but that didn't help. I'm thinking the spring may be too stiff or that it needs a new inhalation diaphragm. Of course, the diaphragm in this is quite large compared to most 2nd stage diaphragms, but maybe one of you would know what would work in this regulator. Any help would be appreciated.

[Gomez' echo]

I am not a service tech, but I do have the Maintenance and Repair manual for the Trieste. Under the trouble shooting chart, here is what it says for "Hard to breathe"
Origin: Demand lever (Part No. 85-854) Lever set too low. Adjust height of lever.
Regulating Nut (Part No. 85-419) 1st Stage pressure adjustment too low. Turn clockwise to increase pressure. Employ 85-1015 gauge in low pressure port. Recommended pressure 125#. Maybe this is helpful.

[Gary]

Thanks for your reply, but I already have the Trieste service manual and followed the adjustment recommendations. I am a service technician in a dive shop in North Florida so I have access to lots of parts and manuals. If someone knows a trick or two to get this to breathe better, I'll probably be able to find the part in the vast sea of junk that accumulates under my bench. ;D

[JES]

Gary,

Try to touch base with Dan Barringer (of Vintage Scuba Supply fame). He overhauled my Trieste II and did a superb job!

He probably has a trick or two up his sleeve.

[admin]

Gary;
I've rebuild many Triestes and they weren't ever that good of breathers- they never breathe as well as a Royal or Mistral. I figured the problem had to be the small LP diaphragm (as compared to all other two hose regulators). No other two hose regulator had that small diaphragm and even the new Mentor has one that is the traditional size. I did an experiment and modified a Trieste to use the full size USD boxes and diaphragm. It breathes great (1/2 inch cracking pressure)- as good as any Royal or Mistral. Now I have a two hose regulator that is two stage, balanced and has an LP and HP port. It's my answer to the $1000 Mentor.
Dan

[SeaRat]

Gary,

There are three design problems with the Trieste II:

--The diaphrigm is built too "stiff." It has a permanent flex which must be overcome with suction pressure. This amounts to about 1/2 inch of water pressure added to the mechanism.

--The demand venturi is not correctly set. There is too much venturi going into the case, and not enough down the hose.

--The venturi vent can move a bit, and not be pointed directly down the hose. The grove on the side is not quite right for the correct setting.

Here's how I overcame these problems:

--I manufactured a new diaphragm out of waterproof, flexible material. I attached the metal part of the diaphragm with glue (I got the metal part from a different old diaphragm; and kept the original intact). I greased both sides of the boxes, and put then put a "shoegoo" rubber cement onto it, placed the diaphragm onto it, then put the bottom box on it, and a book or something onto it. I let it dry for 48 hours, then trimmed off the excess material, opened the boxes, and removed the diaphragm. I let it "cure" for another 48 hours, then assembled the two. Dan overcame this by changing the case, and in doing so changed the diaphragm. I like my way better, as it preserves the character of the regulator. This resulted in much better performance, especially with the other three measures I took.

I years ago sent my Trieste II to a shop in Vancouver BC. They specialized in a modification which involved plugging one of the venturi ports on the side. They used soldier (use a lead-free variety). This increases the amount of air directed down the hose.

I placed a block in the mouthpiece to keep air from going into the exhaust hose. I used the same block that is found in a Healthways SCUBA Delux two-hose regulator, but I glued it into the AMF Voit mouthpiece. It is a round plexiglas disc with holes about 1/16th inch in diameter around the perifry of the disc. This blocks the air from going down the exhaust hose, and channels it into the mouth.

Finally, I fine-tuned the LP port by screwing it out until it matched the interstage pressure. I then exactly matched it to the opening of the inhalation hose (it moves about 1/8th inch).

With these fixes, which I've been using for about 15 years now, this becomes my favorite two-hose regulator. It pulls about 1/2 inch of water suction pressure. I recently upgraded it with Dan's grey hoses (boy to they look good), and a new flutter valve (Dan's fit the Trieste II very nicely, and are sturdy too).

Good luck with it.

John

[JES]

SeaRat,

Great post!

You and Dan are right on the money about the Trieste II.

I own one and just love it. 3,000 psi capable with LP & HP ports. However, my Royal Aquamaster without questions breathes much easier.

Funny thing, I dive the Trieste II much more. I really like my SPG on the Trieste so that there are no questions about remaining air.