J valve question

[Goodlifedivers]

Is there any way to tell if a j valve has been deactivated?

[ScubaLawyer]

Not sure what you mean. Are you talking about a missing stem or valve assembly? I would imagine that would leak. If you are talking about on or off as long as the knob is installed correctly, down is reserve activated. Not sure what your question is. Mark

[Goodlifedivers]

I was told early in my diving that most j valves that went through at least the dive shop I used to visit were "deactivated" or made into normal tank valves were you didn't worry about pulling it to activate it.

Was I lied to or did I get some terrible information?

[Ron]

I have personally rebuilt and used at least a dozen vintage j valves. The only ones I have ever seen lock wired in the down position are some US Navy ones from the 90's and after. Most of the people here use the J valve as it was designed, that is in the up position while diving. Some military guys flip the valve handle so reserve is down and not up, and some guys don't use a pull rod, but I would say most of us use them the way they came. One of the PADI manuals says this same thing that you heard, but I have never seen anyone in the real world actually do it.

One of the engineers can speak to the technical specifications of the average j valve, but they are entirely safe and useful if you use a good one, like one made by US Divers. The U.S. Navy still uses them.

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[Ron]

Additionally, I saw that you mentioned that you were not sure if the valve worked. A super easy way to test this on land is to take a tank with about 600 psi in it, flip the j valve lever in the up (reserve active) position, then open the tank in your garage or driveway. You will hear the tank bleed down like normal, then you will hear it get much quieter as the reserve spring force and force of the air in the tank approach being equal, which will restrict air flow to the opening of the valve. If you close the main valve knob, then use a pressure checker or regulator, then you will have an idea when your particular valve begins to exert enough spring pressure to stop air flow. You can also test this under water.

If the valve is out of the tank you can always blow through the dip tube with the valve open and move the j valve lever to see if it restricts air flow that way as well.

This is not a technical explanation. If you would like one, then again I would refer you to one of the engineers here.

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[ScubaLawyer]

I suppose you could super glue the reserve assembly to the valve stem in the open position but in my 48 years if diving I've never seen it done. I have seen the occasional J Valve left in the open position and the knob removed for folks that don't want to have to worry about it. I've rebuilt enough valves now to be pretty confident a J Valve is either on or off. There really isn't a middle ground, at least for the USD and Sherwood valves I've worked on.Mark

[ScubaLawyer]

I also defer to the fine engineers on this forum.my knowledge is practical, not scientific.

[Ron]

I have to side with Mark on Sherwood valves. I still have one I got from a friend that has never been rebuilt and it has to be from the late 60's or early 70's as it says selpac on it.

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[luis]

The easiest way to disable a reserve is just to remove the internal mechanism (for US Divers, Sherwood, etc.), but I don’t know that anyone has done it as common practice.

If you know how it feels to open the reserve, you can normally feel or hear a click, it would be easy to tell if the mechanism is missing. You can also test it like Slonda described above.

Also, if the mechanism is in place (and somewhat functioning) you will not be able to fill the tank with the reserve lever in the up position.

I have seen tanks were they removed the lever, but IMHO, that is a bad practice. It leaves the stem exposed to damage. I also like to see that the reserve it actually open.

[Herman]

Another easy way to get an idea if it's working or not is to put a reg with a SPG on the tank, put the valve in "dive" position and breath off the reg while watching the SPG. If it rocks several 100 psi then you are pretty sure it is working. Flip it into reserve and the rocking should stop. If the tank is close to empty, just breath it down on land (reg with SPG would be best) and see what happens, it should get hard to breath from somewhere between 300 and 500 psi and get easy again when you put it in reserve.

[Goodlifedivers]

By "dive" position you mean it should be in the up position (assuming it's a standard valve)?

My plan was to just dive it until empty with a class but after about 1:30 class was over and nothing happened yet so I checked the pressure and it was just below 1000 so I still had some time to go.

I'll try bleeding it tonight and see.

[Bronze06]

Just a reminder that you fill a tank with a J valve in the reserve activated or "down" position. After filling, place the valve in the deactivated or "up" position. Solonda's right about Sherwoods, they are fricken bomb proof. Most j valves have markings on the lever that will tell you where up and down are.
ALWAYS STORE the valve to the UP position AFTER FILLING! If you don't the valve will lose its ability to retain a reserve of air due to spring compression. I know a lot of you guys already know this stuff, but here it is again.

[Ron]

Just to reiterate what Russ said, because it can be confusing, the lever up reserves air, the lever down does not in the normal mode of operation.


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[Goodlifedivers]

Ok so the j valve works fine. I noticed the dip in pressure as I breathed in and noticed the diff breathing with the pressure less than 500 psi.

The spg kicked back up to 500 once I activated it. Works fine to me.

[Ron]

Now that you will dive it, I would note when you start feeling that the regulator feels difficult to breathe, then ascend. Use your pressure checker or SPG to note the pressure at which that occurred, then write it on your tank with a sharpie. That way, if you are diving without a SPG, you generally know the real pressure at which you would ascend when you pull the j valve lever. All of mine are between 300-600 psi.


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