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Fibonacci
Master Diver
Posts: 104
Joined: Wed Oct 19, 2016 5:08 pm
First Name: Graeme
Location: Melbourne, Australia

Snark III IP issue...

Sun Mar 08, 2020 9:06 pm

After finishing a couple of other Sea Hornet projects, I'm finally getting around to assembling my late model Snark III DH (HP port + OEM LP adaptor).

While I'm new to the vintage DH overhaul scene, I have restored a Spiro Royal and a couple of RAMs successfully so I have a fair idea of how to go about it using some of Herman's specialist tools... which makes it easier!

The reg itself was in very good original condition, little used and obviously well looked after.
A full strip down and light pickle in 50:50 white vinegar and water, rinse and ultrasonic clean in Simple Green ended up with sparkling chrome.

My problem arose when I started reassembly...
The official Nemrod repair guide I was able to download says with a tank pressure of 2,500psi IP should be 130psi.
First screw the IP adjust screw #21 flush with its housing #20 on initial assembly, then to screw it deeper to get an IP of 210psi and set the OP release valve to pop. Finally back off to 130psi purging repeatedly.

Despite a new diaphragm of correct thickness (much thicker than a RAM) with two washers when the IP adjust screw #21 is flush with #20, the IP is only 70psi. I have to really screw it in deeply to get an IP of 130psi let alone 210psi to set the OP valve... and the mainspring seems VERY compressed.

Adjustments seem very finicky vs a balanced RAM, I've looked at the sticky re setting a DA Navy Approved but not sure it applies to an upstream reg?
https://vintagedoublehose.com/forum/vie ... =12&t=6892
Also the adjust screw cap is very thin with little bearing surface vs a RAM or current Aqualung equivalent and tends to cant and gall under spring load.
Small movements may or may not alter the IP in a consistent manner!

So I'm stumped... any advice from DH Snarkologists gratefully received!
Snark III IP_1.jpeg
Snark III IP_2.jpeg
Snark III IP_3.jpeg
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'A man can never have too much red wine, too many books or too much ammunition' Rudyard Kipling

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Herman
VDH Moderator
Posts: 1271
Joined: Thu Oct 25, 2007 1:45 pm
Location: Raleigh NC

Re: Snark III IP issue...

Mon Mar 09, 2020 6:04 am

My first thought is a weak spring. Do you have one you have a different one you can test with?
Herman

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Fibonacci
Master Diver
Posts: 104
Joined: Wed Oct 19, 2016 5:08 pm
First Name: Graeme
Location: Melbourne, Australia

Re: Snark III IP issue...

Mon Mar 09, 2020 6:19 pm

Sure, could be but I don't have a spare mainspring and Snarks take a unique size :(
This one is in great condition, so I'd love to get it sorted out!
220 BAR IP.jpeg
Snark III label.jpeg
Yoke was updated to handle HP using an old Scubapro part, the counterbore was the perfect size, just needed the bore enlarged from 23.15mm to 23.50mm. A reamer would work better if doing a few of them :D
Sourced a Nemrod OEM LP adaptor and fitted an XS SCUBA swivel T piece which routs LP hoses well and is quite robust.
Snark III yoke.jpeg
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'A man can never have too much red wine, too many books or too much ammunition' Rudyard Kipling

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