Need help disassembling J-valve

[rx7diver]

Members,

I am attempting to disassemble my just- purchased U.S. Divers J-valve. Quick question: How do I remove the internal brass "switch" reserve part? You know, that part that "clicks" on/off? (See 2nd pic.)

Thanks in advance.

rx7diver

 

[Luis H]

As far as I recall, just carefully grab it with a pair of needle-nose pliers and pull it out.
If it is a bit stuck, you may want to soak it first.

 

[rx7diver]

As far as I recall, just carefully grab it with a pair of needle-nose pliers and pull it out.
If it is a bit stuck, you may want to soak it first.

Thanks, @Luis H . I was thinking to do this, but I was afraid I'd screw something up--since the piece seems to be under spring tension.

rx7diver

 

[Luis H]

You can download a service manual from VintageDoubleHose.com

The diagram is always helpful, but there is a full service manual that is available.

Good luck.

 

[rx7diver]

UPDATE: Well, I think I put everything back together correctly. (See attached pic.) I elected to NOT disassemble the reserve mechanism part. It occurred to me that its spring is set to allow the mechanism to engage/disengage at a certain prescribed cylinder psi, and I didn't want to screw this up before I had actually breathed off of a regulator attached to the J-valve.

Turns out that the valve closes off at approx 200 psig. Maybe the old spring has weakened?

I was thinking that the valve should close off at more like 350 psig. My quick back-of-the-envelope calculations suggest that ~115 psi would be required for a 60 fpm direct ascent from 130 fsw to the surface for a diver using an old-school steel 72 and having a SAC rate of 0.5 cfpm. So, closing off at 350 psig would allow for this ascent while keeping enough remaining air in the cylinder.

Comments?

ETA: It just occurred to me that maybe my Scubapro SPG is not reading so accurately so close to zero...

rx7diver

 

[tursiops]

UPDATE: Well, I think I put everything back together correctly. (See attached pic.) I elected to NOT disassemble the reserve mechanism part. It occurred to me that its spring is set to allow the mechanism to engage/disengage at a certain prescribed cylinder psi, and I didn't want to screw this up before I had actually breathed off of a regulator attached to the J-valve.

Turns out that the valve closes off at approx 200 psig. Maybe the old spring has weakened?

I was thinking that the valve should close off at more like 350 psig. My quick back-of-the-envelope calculations suggest that ~115 psi would be required for a 60 fpm direct ascent from 130 fsw to the surface for a diver using an old-school steel 72 and having a SAC rate of 0.5 cfpm. So, closing off at 350 psig would allow for this ascent while keeping enough remaining air in the cylinder.

Comments?

ETA: It just occurred to me that maybe my Scubapro SPG is not reading so accurately so close to zero...

rx7diver

View attachment 693505

As I remember, those valves were set to open at about 500 psi.

 

[rx7diver]

As I remember, those valves were set to open at about 500 psi.

Yes, I just read the service "manual" that @Luis H suggested (that's on the VDH web site): ~500 psi.

Thanks,

rx7diver

 

[Luis H]

Single cylinder reserve valves like this one was always advertised (in the US Divers catalog) as 300 psi.

In my experience, they were never too precise, but 200 psi is a bit low, but I am not surprised.

As far as I remember, the reserve assembly in this valve came out as a unit. It was not designed to be disassembled into its parts, the spring was captured between the end with the seat and the cam.

 

[rx7diver]

Single cylinder reserve valves like this one was always advertised (in the US Divers catalog) as 300 psi.

In my experience, they were never too precise, but 200 psi is a bit low, but I am not surprised.

As far as I remember, the reserve assembly in this valve came out as a unit. It was not designed to be disassembled into its parts, the spring was captured between the end with the seat and the cam.

Yes, I just did some more googling. Downloaded a manual from the Agua Lung web site ("Military & Professional Operations; Authorized Technician; Technical Maintenance Manual; J, K, Z and Twin Manifold Valves," Rev. 03/09). On Page 10 is the statement, "Acceptable reserve actuation pressure ranges: (single cylinder) minimum of 450 psig, (double cylinder) 225 psig."

rx7diver

 

[Luis H]

Can you post a link to that manual?

Thanks