J-Valves

[ebj]

I have J-valves on three tanks, One is a Dacor and the other two are U.S. Divers. The Dacor valve cuts off the air supply completely at around 400psi, flip the reserve lever down and breath the remaining air. Both U.S. Divers valves never cut the air supply completely off. The breathing does get a little labored around 450Psi, but never shuts off completely like the Dacor. Flip the reserve down on the U.S. Divers valves at around 400psi and breathing is back to normal.
Are the U.S. Divers valves working properly? Maybe some manufacturers valves were set up different?

[luis]

I have J-valves on three tanks, One is a Dacor and the other two are U.S. Divers. The Dacor valve cuts off the air supply completely at around 400psi, flip the reserve lever down and breath the remaining air. Both U.S. Divers valves never cut the air supply completely off. The breathing does get a little labored around 450Psi, but never shuts off completely like the Dacor. Flip the reserve down on the U.S. Divers valves at around 400psi and breathing is back to normal.
Are the U.S. Divers valves working properly? Maybe some manufacturers valves were set up different?

As far as I can remember, that is the way they both worked. Some reserves had a tight sealing seat and some didn't. Like Scubapro DCAR valve didn't even had a real seat. It just had a brass plunger that restricted the air flow. The reserve doesn't have to totally seal.

[ebj]

Thanks Luis. It's good to know they are working ok. They come in handy when I miss the mark in in my dive times, allowing me to get max bottom time on the regs that cannot use a banjo.

[jamiep3]

I have one J valve, that you can breath with difficulty below 300 psi, but if you open the tank valve without a regulator attached, air does not come out.

Go figure.

[treasureman]

Before the computers to dive with and fancy watches, there was the J valve. Simplicity itself, to be replaced with a K valve. wonder why.

I stiull got my J's and they do the job. No need for extra hoses. Keeps my diving simple..just the way I like it

[duckbill]

I just had my first J-valve malfunction last week. My set-up is an old 1/2" USD manifold on twin-38s. Typically, the J trips to give 400 psi equalized pressure, and the cylinders "sing" to me as I get down near the time to trip. When the malfunction occured I noticed that the dive was lasting longer than usual, and that the cylinders weren't "singing". I kept watch as the gauge metered near 100 psi and got in a position near the surface since I suspected trouble. When I felt the resistance, I tripped the valve and the cylinders equalized to only 180 psi! Up to the surface I went and ended the dive. Had I not been familiar with my own set-up or been less experienced I could have been in trouble.
I checked the valve, and sure enough.... she was leaking. The valve must have been slowly leaking throughout the whole dive- enough to leave me with just a little to spare. I suspect the flow check/seat interface or some debris between them. Any suggestions are appreciated. Can these parts be reconditioned, or will I need to replace them? I hate to have to disassemble the manifold. The LDS had a heck of a time getting the union to seal on that side at the last visual. They ended up polishing the mating surfaces. I wonder if they got some gunk in the J-valve area. Hhhmmm!

[duckbill]

Some reserves had a tight sealing seat and some didn't. Like Scubapro DCAR valve didn't even had a real seat. It just had a brass plunger that restricted the air flow. The reserve doesn't have to totally seal.

I know that doubles weren't being referred to in the original question, and Luis wasn't specifically talking about USD J-valves, but he does bring up a point which is related to something I've been wondering. Maybe someone can help to explain this to me. It may even help conclusively answer the original question posed by ebj.

I have never dived a single-type early USD J-valve, so I haven't experienced this leakage which is being described, but this subject has come up before and so I am curiuous. I can see where this described "restriction" design would work for a single cylinder type J-valve, but not for doubles.
So, specifically regarding the old USD 1/2" J-valves and 1960 series (3/4") J-valves:
The single cylinder-type J for either model had J-valve parts which were identical to their manifold-type J counterpart. A single J-valve could be designed to allow some bypass of air once the valve seated and the diver would still feel the resistance. However, on doubles, one cylinder drops pressure to whatever the J-valve is rated before it allows air to drain from the J-valved cylinder to maintain the designed pressure differential between the two cylinders. That is why the gauge pressure drops so rapidly in the first part of the dive on j-valved doubles. For the remainder of the dive there is a, say 700 psi, differential between the cylinders due to the action of the J-valve, until the non-J-valved cylinder pressure drops to a point where breathing resistance is first felt (say 80-100 psi on my DAAM). Then, when the J-valve is tripped, the 700 psi differential equalizes to 400 psi as it should. If there were any leakage through the J-valve other than to maintain the 700 psi differential, then less than the expected 700 psi differential would exist. The longer the dive or the worse the leak, the less the differential between the cylinders at the time the J-valve is tripped and there could be no reliable consistency from dive to dive.

Now, the flow check/disc-and-retainer part numbers are identical for either the single J or the doubles J. Does some design difference exist in the J-valve portion of the valve casting of the single-cylinder J (like a bypass port) which would cause a designed leakage in the single-cylinder type, but not the one made for the doubles manifold? If not, then I would have to conclude that a leaky 1/2" or 1960 series USD J-valve would be defective, whether on a single cylinder, or a doubles manifold.

I hope this isn't confusing.

[Bryan]

Tom Madere (Captain) is the best man I know with USD valves. Plus I have shipped him every original NOS USD valve part that I could get my hands on in the last 2 years. I'm willing to bet he can either make the repairs for you or at least supply you the parts to make it happen.

[captain]

Over the years the USD J valves design was changed but I can not say when the changes occured. It appears that the early valves had a hard round metal seat similar to a BB. Later valves had what appears to bea plastic or nylon seat and most by now are hard and crumbly especially so for the old 1/2 " valves. Later valves with the black plastic knobs is a totally different design and I feel the best. Unfortunatly I have no NOS seats and if I did they probably would also be hard and crumbly. I did experiment with replacing the seat in one of my valves with some sucesses but it is difficult, about in the same league with replacing HP regulator seats. I would be happy to take a look at your valve. I would only need the J side not the whole valve.

[duckbill]

Thanks for the offer, Captain.
First I'll try cleaning it up. Then, I have some other USD J-valves from the same period which I may cannibalize if need be. The flow check is the metal, spherical "BB" type (it is dated 8/57). If I can't get it to seal properly by the off-season this Winter, I may take you up on your offer.

[captain]

There are a couple things you can try. One is to shorten the pin that pushes the ball off the seat by about .010" It is possible it is too long and not allowing the ball to seat firmly. Second you could try to shim the spring that pushes the ball against the seat with a small flat stainless steel or brass washer. I don't think you will ever get a leak free seal with the metal ball seat.

[duckbill]

I don't think you will ever get a leak free seal with the metal ball seat.

I know what you mean. Quite a few of the sealing surfaces on those old manifolds are metal-to-metal: the union connections; bonnet nut to valve body; and the ball J-valve seat. They are all a PITA!
Great suggestions. Thankyou. The washer would also give me more reserve. I'll give your ideas a try if cleaning doesn't do the trick. Since it was a sudden problem, I am hoping it is just an very small piece of debris holding it open.

[pescador775]

duck man:

The original seats were made of crappy phenolic. In the 1970's, due to failures or these mechanisms reported in the dive press, US Divers changed the seat material to delrin. I have a few of these, NOS. If ducky needs one I can supply for 10 bucks.

The seat and spring are held in place by a brass threaded plug. An allen wrench is required to remove. If, by some miracle, you can successfully remove this plug without cracking, drop me a line.

How is the Sea Hunter working--kill some fish, yet?

[pescador775]

OK, reading farther on I see you have the ball bearing check.

Also, after reviewing, it looks like the newer seats are made with a hard nylon core, not delrin. Same difference, I guess.

[duckbill]

How is the Sea Hunter working--kill some fish, yet?

Hey, Dennis! Wasn't sure that was you at first. No fish yet this season. Other than a Southern California trip earlier this Summer, I haven't been doing any ocean diving. I didn't want to chance breaking some regulation while down there so I didn't take the gun with me. The 'Hunter' is all fixed up and ready to go- new bands, line release (thanks to you!), and all. I've been doing a LOT of diving with the salmon in the river here which are in a holding pattern for the soon-to-be-opened fish ladder. Temptations, temptations!

Yes. My J has the metal ball type check valve. I know the retaining screw is good to go because I've had it apart for cleaning not too long ago. Thanks for being willing to help though.