Questions about J valves

[Eric Sedletzky]

I have a bunch of 72's but none of them have J's on them. With this new DH toy of mine I want to get a couple J valves and change out a few tanks because I want to try vintage.
My questions:

How do J valves work internally? Do they need to be rebuilt or any kind of mainenance. Is there anything inside that can fail making the lever not do what it needs to do.

When the lever is up, how does the breathing difficulty happen. Is it sudden or is it gradual. And when you pull the lever down what does the PSI generally go up to?
After the lever is pulled down is the breathing back to normal or is it somewhat restricted?

I also have a source to buy as many used 72's with J valves that I could possibly want. Getting the valves is no problem. I guess I will just look at the tanks and valves and pick the best ones I see. Are there any year perameters that anybody knows are better than others, or should I just grab the newest ones according to production date. What about brands - any prefferable over any others?

Fianally, I will have to fab a lever wire out of stainless unless I can find one somewhere. That shouldn't be too hard. I guess I will have to fab some kind of guide rings that will go on the tank bands too. Ant suggestions. I've seen at the bottom of those wires there is a loop or ring to grab onto.

 

[Boiler_81]

When picking a tank with a J valve look for valves which have a high pressure port for attaching a SPG. You don't have to use it but it is a nice option to have.

 

[simonbeans]

All good questions. Best answers will be given on Vintage Double Hose That is where the vintage crowd hangs out.
In short, USD are best. Dacor had the HP ports for SPGs, but the location made the handling of the tank by the valve painful. USD parts still available and very easy to service. As per J valve rods, they may be reproduced shortly. Go to VDH and read current thread on that topic.

 

[Gilldiver]

A J-valve has a secondary orifice and seat that is set in line with the main seat of the valve. The orifice and seat are set up in a down stream configuration with tank pressure pushing against the seat and the seat being held against the orifice with a spring.

Ideally, the spring is set so that at 500 psi it put enough pressure on the seat to balance the tank pressure allowing the seat to close the orifice when the J-valve lever is up. When you pull the J-valve lever down, it rotates a cam that pulls the seat off of the orifice letting you have the remainder of the air.

All of the seats for this function that I have seen are not made to deform as they are not made to fully seal the orifice, only slow down the air passage. So, there is not much to maintain on the seat mechanism itself. But there are one or two O-rings on all of the J-valves that I have rebuilt. When you take the J-valve lever off you will find a bonnet that screws out, there may be a O-ring that seals the bonnet to the valve body and another that seals the lever shaft to the ID of the bonnet.

Just take the parts apart and give it all a good cleaning and replace the O-rings. The rest of the valve is just like a normal K-valve.

The breathing will get hard pretty quickly as tank pressure gets close to the spring pressure. The actual pressure that the J-valve will close on depends on the strength of the spring and can be anywhere from 300 to about 600 psi.

 

[porbeagle]

hi zky,
When the lever is up,and you run out of gas,it's the same feeling as with a k valve....depends on your reg.it will either get hard to breath,or you run out of air
When you pull the lever down, your spg jumps to about 1000.(different on other j valves).Simon said it all well but in my experience not just dacor made that HP port. I have J valves exclusively and (without looking)I believe I have HP ports on
my sherwood, US divers and others.But they are great to have if you don't have a banjo fitting. I use the port for a nemrod snark lll.Mistrals need em also.VDH or VSS
is the place to go as simon says D).
OK, thats my 2 cents you might want to wait for the captain to respond though.
OK, 1 more thing... When are you going to make some more Freedom Plates?
I mean like everybody and his brother wants one?
PORBEAGLE

 

[captain]

The J valve is basically a spring loaded back pressure valve. When tank pressure is above 300 psi on a single tank or 500 psi on a double manifold tank pressure overcomes spring pressure and air flows to the regulator. As tank pressure approaches 300 or 500 psi the spring forces the valve to close and breathing gradually becomes harder. They do not shut off abruptly but depending on the type and condition of the seat in the J mechanism they may or may not eventually shut off all air flow until the lever is pulled down to the reserve position.
Most are cam operated and when the lever is pulled down to the reserve position the mechanical cam over rides the spring pressure and forces the J valve open. A simple and extremely reliable mechanism.

If you have a J valve or regulator with an SPG attached when the J valve starts to close at at 300 to 500 psi you will see the SPG swing down to near zero on each inhalation. You can also expect to see a 300 or 500 psi swing in the SPG on inhalation even when the tank pressure is high because the no matter what the tank pressure is the spring pressure has to be overcome before air will flow from the tank to the regulator. Sometimes you can also tell if the J valve is or isn't in the reserve position by the sound of the air flow during each inhalation.

The biggest issue with J valve is something snagging the pull rod and pulling it down or not starting the dive with it in the reserve position. Just as you check your SPG you should also check the position of the J valve during the dive.

 

[Eric Sedletzky]

[/Quote]
OK, 1 more thing... When are you going to make some more Freedom Plates?
I mean like everybody and his brother wants one?
PORBEAGLE[/QUOTE]
I have one plate left if you want it. It's a 3/16" aluminum version, flat on the back (no rail or bracket) The specs are 14.5" tall x 12' wide aty the base. It weighs 1 lb 9 oz.
I want $100 for it plus shipping. PM me if you want it. The cost is the same as the 1/4" ones because the cost is all in the labor. The difference in material is a drop in the bucket
Seriously, this really is the last one I have at the moment. I can't tell you when I'll make another run of 1/4" Al plates or 10 GA s/s plates. As soon as works picks up and I can finance it I will do it. I do the plate thing on the side, there really isn't much money in it. I do it more because I like to contribute to minimalism. I also despise poodle jackets and want to screw up their world and their mindset as much as I can even if it's a drop in the bucket, I still feel I've done my part to change the direction of diving.
I better stop, I need to be nice.

Thanks for the responses everyone, I really appreciate it.

 

[Slonda828]

The only thing I will say about getting used to J valves you may already know. I would test the PSI that your reserve activates at. I have one that is a 500 PSI valve and another that is a 300 PSI valve. Neither are depth compensated, so the reserve pressure is the same regardless of the depth at which you hit the lever. This took a while to figure out when I did my gas planning, as I wanted to make sure that if I had to pull the lever, I had enough time to make a safe ascent from the depth I was diving. I know you are already a very seasoned diver, but the first time I had to pull the lever was at 80 feet, which lead to some rather hasty math on my part with my 72CF tank. I will tell you one thing though, I can track my SAC in my head now that a lot of my diving doesn't involve an SPG.

Diving with a J valve is a liberating experience, especially if you forgo the octo as well. There's nothing like one hose and no BC to really make that dive seem free.

 

[Nemrod]

They are fairly maintenance free. Main thing is to check that it works before you need it. They can be adjusted by shimming the spring etc. It is an odd thing to watch the spg needle to swing as you breath but then most people don't use an spg with a J valve, lol.

During the dive frequently check that the lever is up. I often do not use the rod, just reach back with my hand. When you work on the valve make sure the cam goes back--and check by testing--that UP is reserve and DOWN is reserve actuated. That can be an issue if you flip it and don't test--lol.

Yes, down with poodle jackets, down with the man, up with minimalism and the stock market, .

Steel 72s, look for those that are galvanized or at least galvanized under the paint. Also, avoid those with the plastic/epoxy/whatever sort of inner lining.

N

 

[halocline]

There's a really good drawing and explanation of j valves in the Vance Harlow book about regulator repair. I'm not sure if you were asking about evaluating j valves only or LP72s as well. In terms of the tanks, I would only buy galvanized ones, and if the paint is peeling over a galvanized finish, it's easy to remove. In terms of tank manufacturers, I bet that the PST ones are the most common. The big issue for me if I were buying several would be if the REE number is available for any of them, which means you could legally get the plus rating. I've inquired on several threads and there's a hydro tester from FL who has been active on some threads, and so far nobody has come out and said "I have the REE number" for any LP72s. I would venture a guess that the PST number might be easiest to track down. If you're filling yourself, or have a filler that will overfill, it's not really an issue.

I got my plate, and it looks terrific. Thanks!