What would you do with a J-valve?

[g2]

pescador775 once bubbled...
...Here's the deal; the J valve, in the 'on' ('up') position can interfere with your SPG readings.

Correctamundo! Since an engaged J-valve mechanism limits airflow, the SPG reading will dance around with each breath -- approximately 200-300psi in my experience. This can be very disconcerting if you haven't used one before ("Is my tank valve open all the way?!"), and may cause problems for some air-integrated computers.

By the way, the poll choice "It doesn't matter. I have a pressure gauge." was kind of a trick answer. I hope the people who chose that option just misunderstood the question; you can't ignore the position of the lever or you might get an unpleasant surprise at about 500psi/30bar (using a single tank).

 

[John C. Ratliff]

Pesky,

I know about the "J" completely restricting the flow. I was simply quoting Fred Roberts, as he wrote it sometime before 1960 (I think, as I don't think he changed it in the 1963 edition).

Concerning the fluxuation of the SPG, that depends upon the design. Some do, some don't. Where it's built into the regulator (yup, I have one of those too), it doesn't usually result in this restriction.

For modern divers, I agree that it's best to ignore the "J" by always pulling the reserve to the down (off) position). This is in line with their training, that assumes there is no such thing as a "J" valve.

But for me, I will elect to keep it on, and use it as I have in the past. By the way, the reserve in the UDS-1 system (a triple tank system) is perhaps the best I've seen. It does keep ~900 psi back, and the SPG goes completely to zero before pulling it. After equilization, there is well over 300 psi it the system (my gauge reads almost 500 psi). I keep it on too, as it's like having an internal pony bottle. 'Same with my doubles (42 ft3 steels and 50 ft3 AL)

SeaRat

 

[pescador775]

John: The UDS definitely had the best J design. For one thing, it was inverted. Also, La Sprirotechnique had the benefit of 20 years design experience resulting in overall improvement on all their later valves (the shiny chrome type). The earlier ones were sometimes iffy and the three piece oxygen type manifold (from the fifties) a real beetch. If you've tried to remove the reserve seat from one of these you may know of what I speak. An allen key is inserted in the threaded end which has a cup shaped plug. Unfortunately, this plug is subject to jamming and when forced, the thing fractures. If you manage to remove one intact best to grease it up good before replacing.

When I dive my triples, the J valve is up. Sometimes, I use an SPG with it, sometimes not. Recently, I had to make a spanner to remove the unusual slotted end plug from the J side. I replaced the leaky Nemrod/Spain washer which seals the stem with an O ring. Works good, no leaks. I test the J valve by running it up to 'on', draining the tanks and listening for any leaks. If no leak, the spring and seat are good. Final test is to trip the valve and let it sing. Same principle applies to a single J except that the main valve needs to be turned on and left on when checking for leaks. I'm sure you know all this stuff but some younger divers might find it of use.

One oddity, the UDS, because of the higher tank pressure does have an elevated reserve setting of 900 psi. However, the Nemrod manifold, designed for 2200 psi tanks, has a 'standard' setting of 700 psi. Since my rig uses the UDS, 3000 psi tanks, there is a bit less time to punch out. Oh well, still enough time for me and insurance if one 'forgets' to read the gauge.

Pesky

 

[John C. Ratliff]

Pesky,

I know what you mean about the conversion of a valve from one cylinder style to another. When I converted my Sherwood twin manifold from a "K" type to a "J" type by buying a like single valve, I needed to order the 500 psi spring to put behind it to get the desiged higher spring holdback pressure.

Incidently, I use this valve on a set of twin 42 ft3 steel cylinders I've had since the 1980's. These are 1800 psi cylinders, and so work well with all my older double hose regulators (I have five that I can dive, four of which I keep around--one is on desplay at the LDS).

John

 

[pescador775]

Right you are; I have a pair of 38's myself, 1900 psi. The Royal Aquamaster and Nemrod Snark III can be used with 3000 psi cylinders, no problem. The Royal is balanced so that the intermediate press does not drop with increases in tank press. It helps to up the pressure in the Royal by a few pounds. Normal is 110-115, I use 120-125 psi. Get the newer yoke if possible as it is strong enough to hold 3000 psi. The Nemrod is unbalanced but the second stage uses a compound lever and extra strong venturi jet which helps a bit. Intermediate pressure is normally set pretty high for a double hose, about 130 psi, and so the drop which occurs at high tank pressure doesn't seem to affect the breathing.

 

[Bob3]

The Snark III even came in a DIN version.
ut:
Got a set of 1958 USN twin 50s, looking to stick a "modern" burst disk in the valve. Any suggestions?

 

[John C. Ratliff]

I finally figured out that my Snark III had a design problem, in that the LP venturi jet ports allowed some of the venturi air to hit the LP diaphragm. I took a piece of plastic I cut from a milk jug, fit it into the regulator above the venturi ports, and with holes in the plastic, screwed it to the interior regulator case screws. It now breaths much better than before I made that modification. I also use USD hose/mouthpiece system on it, or substitute a Hope/Page mouthpiece (I still have two of them) for the original, to get the hose breathing resistance down. It is a very good unit with these modifications.

SeaRat

 

[Hallmac]

extra credit attempt

cause you forgot to turn the tank all the way on before you jumped in


__________
saw it happen once!

 

[pescador775]

Very interesting mods, and clever analysis!! I'm a little bit surprised that the venturi didn't go into 'runaway' when you substituted the low resistance (shorter) hoses and larger check valves of the Hope Page. The USD mouthpiece has really large valves. Does the reg breath OK when diver facing up, on his back?

Years ago, I modified a Nemrod to accept a low pressure hose. Disassemble reg, mill a flat on the side of the low pressure chamber, drill and tap 3/8-24.

Pesky

 

[pescador775]

Bob, I've never actually done it but it should be possible to substitute the disk/plug. The blow out port contains a lead plug, disk and phenolic washer. I would look around the shop parts bin and see if the Thermo kit is sized to replace the old one. Check available pressure ratings. The Thermo normally comes with a 5000 psi or 4000 psi fail disk; too high, but there should be something closer available. Northeast Scuba supply (John's Scuba) is usually pretty savy on these problems.

Edit: I checked and the Thermo fits the old style valves. For a 2250 psi tank you need a disk which is marked '3500'. For an 1800 psi tank, the disk should be '3000'. The Thermo plug for US service uses a commonly available thread size and most shops should have some in stock.