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Post by Fibonacci on Mar 8, 2020 16:25:54 GMT -8
After finishing a couple of other Sea Hornet projects, I'm finally getting around to assembling my late model Snark III (HP port).
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 tools.
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. 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 finicky vs a balanced RAM, as the adjust screw cap is very thin with little bearing surface vs a RAM or current Aqualung equivalent and tends to cant under spring load. Small movements may or may not alter the IP in a consistent manner.
So I'm stumped... any advice from Snarkologists gratefully received!
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Post by vance on Mar 8, 2020 20:49:41 GMT -8
What happens to IP when you set to 130 psi at 2500, then attach it to a tank with, say, 1000 psi or less?
Just a wild shot in the dark... Do you have the correct HP pin installed? There are different ones for different models.
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Post by Fibonacci on Mar 8, 2020 21:28:46 GMT -8
Will try that... have partially disassembled again to recheck but all seems OK.
The HP pin is the original, stepped in three diameters with a dome head. When assembled to the pin pad it travels smoothly and feels no different in action to a RAM 'push button'. The new HP seat supplied by Enrique Dauner has a much larger diameter recess for the pin, so may well be off a later model. I decided to reface the original HP seat which fits precisely around the HP pin.
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Post by SeaRat on Mar 8, 2020 22:06:48 GMT -8
Fibonacci,
I would throw away that repair manual, as I don't think it is correct. There may have been some translation problems, but realize that the basic design of the Snark III has never changed. The Snark III is an unbalanced diaphragm first stage with an upstream second stage, necessitating the Overpressure relief valve (OPRV). Nemrod calls the Overpressure relief valve a "third stage," but it is a safety feature, keeping the regulator from blowing up if the first stage fails.
It sounds like your first stage is holding the IP steady, in which case you have a functioning regulator. Unlike a downstream second stage, the upstream second stage gets harder breathing as the IP increases. Therefore, the IP should not be 130 psig at 2500 psig (pounds per square inch gauge) tank pressure. Remember that with a diaphragm first stage (spring biased diaphragm first stage), as the tank pressure drops, the IP will increase. So at 2500 psig and 130 psig IP, as the tank pressure decreases the IP will increase so that at 500 psig tank pressure, the IP will probably be in excess of 150 psig. You can measure that with your current regulator setting if you wish. (I'm pretty sure that Nemrod never made a balanced diaphragm first stage for the Snark III).
Fred Roberts, in his book, "Basic Scuba," talks about the IP for the Snark III being at about 110 psig. I would say that this should be 110 psig IP at 500 psig tank pressure. It will probably be at less 100 psig at a full tank pressure, which will be really nice for cracking pressure. Once the IP is set, adjust the OPRV so that is just starts to leak, then turn it down a half turn or so so that it stops at low tank pressure.
John
PS, my Snark III is one of my best Breathing regulators in my collection. But I made one small modification to help it along, which I'll talk about later.
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Post by vance on Mar 8, 2020 22:58:04 GMT -8
I'd replace the HP diaphragm with a new USD style. I've used them in several Snark IIIs and Silvers successfully. Try 1 gasket. The original was either paper or phenolic, or both. If you used a nylon one it should work fine, but may be thicker.
A new HP diaphragm should be flat, not formed. The formed shape happens when the pressure hits it. I've never seen a new Nemrod HP diaphragm, so I can't swear that they start out perfectly flat, but I'd be surprised if they are shaped.
John is right. The IP should not be so high at 2500 psi. I've always found about 120 psig at 1000 psi works well. If it gets a lot higher at 500 psi, I'd drop it a bit more.
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Post by Fibonacci on Mar 8, 2020 23:43:26 GMT -8
Hi John and Vance Thanks for the detailed replies... The original HP diaphragm was probably twice as thick as a USD RAM and would have started off flat punched out of the usual sheet rubber insert material.
It had a definite set after decades of spring pressure and used two washers, one rubber against the diaphragm then one nylon... not sure why, but this arrangement is in all the Nemrod exploded views.
I got a replacement from Enrique Dauner which was similar in thickness to the original.
I tried resetting the IP at 110psi on a tank with 40BAR (580psi) and the adjust screw was only slightly below the rim of the spring housing. Breathed great! However, when I then put it on a full tank 220BAR (3190psi) the IP had dropped to just 60psi! Strange... I will try a different USD style diaphragm next.
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Post by vance on Mar 9, 2020 6:37:51 GMT -8
Jump to 130-140-150 at 500 psi and see if you can get a reasonable setting at 220 BAR. I've never tried one at more than 2500 psi!
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Post by SeaRat on Mar 9, 2020 8:47:56 GMT -8
Play around with the IP. Remember that the higher the IP, the worse the breathing on this regulator. I'm not sure that the Snark III was ever designed for 220 BAR (3190 psig). That could be part of the problem. The Snark III design dates back to at least 1963, and hasn't changed much since that time. I wouldn't worry too much about the HP diaphragm and its thickness unless you are really interested in playing around with it.
I do know that the U.S. Navy used the Snark III on its 3000 psig systems, but don't know whether there were any restrictions on the fills (psi-wise). I do know that when I went through the U.S. Naval School for Underwater Swimmers, we used the DA Aquamaster on tanks rated to 3000 psig, but that the school restricted the tank pressure to about 2400 psig. This was before the DA Aquamaster was succeeded by the Royal Aquamaster with a more sturdy yolk.
If this were my Snark III, I'd set the IP at 110 psig at 500 psig tank pressure, and simply restrict the regulator to about 2400 psig (about 160 BAR). That would give you an IP at a full tank of about 90 psig (about 6 BAR), which should give pretty good breathing characteristics even on a full tank. A Mistral at 90 psig tank pressure is a dream breathing machine, and so too can the Snark III be a dream breathing machine.
John
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Post by snark3 on Mar 9, 2020 13:25:40 GMT -8
I have 2 books on the Snark 3. One lists the proper IP as being 130 psi @ 2500 psi tank pressure. At this setting IP should be 120 psi @3000, 150 @ 1500, 160 @ 1000, 170 @ 500, and 175 @ 300. This book says to set the OPV to vent at 210. The other book says the IP should be set at 125, the only mention of tank pressure is under diagnostics and they say test on a tank pressure of 500 psi. This book says the OPV should bleed off pressure above 150, and to set it at such. I think Phils suggestion to set it at 120 on a 1000 psi tank is right on. That should put it at about 130 at 500. I would also be very leery of using it on a tank over 3000 psi. I set the IP on one of mine @ 130 on a 2250 psi tank. I put it on another tank with 800 psi to see where it was, to my surprise still 130. I breathed off the reg until the "J" valve reserve limited airflow, it never budged. I left it on a full tank overnight with the air on, in the morning it was still 130. I shut the air off 8 hours later it was still 130. Why, I have no idea but it breathes great.
I will agree that the Snark 3 is a great breathing reg. One of mine is the best breathing reg I've ever used
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Post by vance on Mar 9, 2020 16:00:14 GMT -8
I wouldn't get too concerned about a 160-170 or so IP at 300 psig tank pressure, unless breathing gets uncomfortable. You aren't going to be even close to blowing a hose at that. But, if you're using an LP port adapter and a safe second, that will be too high for the extra second stage.
I'm with John. 3000 psig and above is too much for these regulators. Limit your fills and you'll be happy with it.
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Post by SeaRat on Mar 9, 2020 18:09:30 GMT -8
I just checked my Nemrod Snark III out on my 3000 psig AL 45 tanks, and it worked well at 2800 psig. I then put it on a tank that I knew was low (how low, I didn't know). It breathed well, with a very low breaking point, but with a diaphragm lag. I put the gauge on it, and it didn't register--it was at zero guage pressure, and still functioned pretty well. (I need to get a fill on that steel 72. .) I could not get an IP on this regulator, as my gauge, even with an adapter, could not screw into the OPRV port (it was too large in diameter). So I don't really know the IP on my Snark III (I set it about two decades ago). I promised above to say how I modified my Snark III to give better breathing. Well, I actually did two things. First, I noted that the Snark III's Venturi was compromised by the flow up toward the diaphragm. I don't know if subsequent models have this problem, but early ones tended to shoot one or two of the nozzles up toward the diaphragm, so as to push it upwards when the air was flowing. I reasoned that if I placed a buffer plate of some sort above the nozzle, but below the diaphragm, this air flow against tnthe diaphragm would not occur. So I made a buffer out of a plastic milk jug (I figured that if the plastic was good enough for food, it was good enough for breathing air). I cut it is such a way as to be able to be secured by two of the screws that held the box to the regulator mechanism. Here are several photos of this modification: Snark III Baffle2 by John Ratliff, on Flickr Snark III Bafle3 by John Ratliff, on Flickr Snark III Baffle4 by John Ratliff, on Flickr As you can see, this completely blocks the air flow upwards toward the LP diaphragm, and diverts it into the intake horn. This makes the breathing extremely good for this regulator. The other thing I did was to replace the Nemrod Snark III mouthpiece with a new one, which I received from Vintage Frank (Frank Werthwein) here on Vintage Scuba Supply's discussion forum (My wife and I were visiting Germany a few years back, where my son Nathan was working in a post-doc position at the Max Plank Institute for Intelligent Systems. He gave me a replacement mouthpiece for the Snark III, a Seibe-Gorman(?)* that he said fit the Snark III hoses. IMG_1424 by John Ratliff, on Flickr John *I believe this is a Seibe-Gorman mouthpiece, but The Scuba Museum calls them an Avon mouthpiece. www.thescubamuseum.com/Online%20Store/onlinestore.htm#!/Avon-hose-assembly/p/68521579
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Post by Fibonacci on Mar 9, 2020 20:05:54 GMT -8
Thanks for some new areas to try, will have another play tonight. Yoke was updated to handle HP using an old Scubapro part, the collar nut counterbore was the perfect size, just needed the bore enlarged from 23.15mm to 23.50mm. A Metric reamer would work better if doing a few of them! Sourced a Nemrod OEM LP adaptor and fitted an XS SCUBA swivel T piece which routs LP hoses well and is quite robust. In the meantime, here is the culprit!
Snark III label by Graeme Cameron, on Flickr Snark III yoke by Graeme Cameron, on Flickr
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Post by SeaRat on Mar 9, 2020 22:07:48 GMT -8
I have 2 books on the Snark 3. One lists the proper IP as being 130 psi @ 2500 psi tank pressure. At this setting IP should be 120 psi @3000, 150 @ 1500, 160 @ 1000, 170 @ 500, and 175 @ 300. This book says to set the OPV to vent at 210. The other book says the IP should be set at 125, the only mention of tank pressure is under diagnostics and they say test on a tank pressure of 500 psi. This book says the OPV should bleed off pressure above 150, and to set it at such. I think Phils suggestion to set it at 120 on a 1000 psi tank is right on. That should put it at about 130 at 500. I would also be very leery of using it on a tank over 3000 psi. I set the IP on one of mine @ 130 on a 2250 psi tank. I put it on another tank with 800 psi to see where it was, to my surprise still 130. I breathed off the reg until the "J" valve reserve limited airflow, it never budged. I left it on a full tank overnight with the air on, in the morning it was still 130. I shut the air off 8 hours later it was still 130. Why, I have no idea but it breathes great. I will agree that the Snark 3 is a great breathing reg. One of mine is the best breathing reg I've ever used Okay, I suspect that you have a balanced first stage! Someone either changed this regulator's first stage, or you have something I didn't think existed, a balanced Snark III. I know that a group that was on Facebook from Turkey made a brand new first stage for the Snark, which they called the Snark IV, which incorporated LP and HP ports, and may also have been balanced. Let us know a bit more about this regulator, please. John PS, I just found this history of the Snark III on the CG45 website: www.cg-45.com/regulators/Nemrod/
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Post by Fibonacci on Mar 10, 2020 13:42:51 GMT -8
OK I played around with the IP a bit more last night on tanks with 40BAR (580psi) 110BAR (1600psi) and 210BAR (3045psi). Very finicky to adjust, the smallest changes can mean sudden jumps of 10-20psi. Finally got it locking up solidly and repeatedly 120psi at 210BAR, left it for a couple of hours pressurised but then the HP seat developed some creep. Grrr... 200-210BAR is definitely the upper limit despite the heavy duty yoke! I have another late model Nemrod NOS HP seat but it seems these take a different larger diameter pin than the three stepped diameter style I have now. Anyone know the dimensions of a late model Snark III pin? Can a USD pin be cut down? One other issue is sourcing an octo that can handle an IP that swings from 120-175psi. Given the first stage is unbalanced, a balanced adjustable second like a Scubapro G250 seems like a good choice? What are others using? Fascinating Nemrod history link, thanks
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Post by nikeajax on Mar 10, 2020 15:05:43 GMT -8
I don't remember what your seat looks like, as I sold my S3 to PY a few years back, but it sounds as if your seat iffy... Can it be polished out? What you're describing sounds like something very small is stuck in it where it makes contact with the volcano orifice causing it to creep. One of the things I had drilled into my head from restoring old cars is, "Just because it's a new part doesn't mean it's good..." Just brain storming, and I don't mind being wrong JB
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