Quick question for J valves

[Scuba Bud]

Hey guys,

So I rented 3 tanks from a LDS and I only realized when I got home that they have J valves on them. I've never used a J valve before so I just wanted to ask here before the dive! Basically if I have the lever in the up position then the J valve will act as it should (going to 500psi, getting hard to breath, pull J valve to release rest of air). But if I start my dive with the lever down, past the click, then the reserve is essentially already pulled and it will act the same as a K valve.

Is that right?

Thanks!

 

[eponym]

Sounds right.

See this thread from a few years ago for full details:

http://www.scubaboard.com/forums/tanks-valves-bands/158135-how-does-j-valve-work.html

-Bryan

 

[herman]

Yep, you have it. The reserve pressure can vary between 300 and 500 psi. If you start with the lever in the up (dive) position and you watch your pressure gauge, the SPG needle will swing. While an indication of a problem on a K valve, this is normal on a J valve, it is the reserve parts doing their job. I would suggest you put the valve in the up(dive) position, look at your SPG while breathing to see how it reacts (just for your education) and then put it in the down (reserve) position and do the dive as normal. In the unlikely event you get the knob in the reserve position by accident (dummy DM grabbed the wrong knob to check your air ) you will have seen the effects and know how to deal with it.

 

[Leadking]

A nasty piece of equipment. ALWAYS use your spg and NEVER rely on the reserve. Anyone who showed up on our dive boat with one of these, we would throw the actuating rod in 500' of water.

 

[herman]

A nasty piece of equipment. ALWAYS use your spg and NEVER rely on the reserve. Anyone who showed up on our dive boat with one of these, we would throw the actuating rod in 500' of water.

.......never mind.

 

[Leadking]

.......never mind.

Got your rant before you edited.
Part of the Scubaboard Forum is to be inform readers other than the poster and not have to ask duplicate questions.
Our dive club banned them from the boat due to the MULTIPLE out of air situations that occured with the J valve. When you needed it the the most it, the reserve air wasn't there. They always seemed to have been bumped into the downward position and actuated somewhere along the dive.

 

[KY_BOB]

I didn't see the rant. I personally own 3 old LP72's that had J valves in them when I bought them. I have since replaced one with a K valve and doubled the other 2 with a modern manifold. That suits my type of diving. Herman enjoys diving vintage gear and is very experienced in it. I see zero harm in that.

I do agree that relying on a J valve and no SPG the way the did in the 70's and earlier is risky if your not trained or experienced with them. Personally, I'm not familiar with diving that way and I would not because I don't know what I'm doing and admit it. I also won't go into a cave because I'm not cave trained.

I think that throwing an actuating rod away is a bit extreme. If a person knows what they are doing and especially if they have a SPG. I see very little danger.

The surprising thing to me is that there is still a dive shop out there that will rent you a tank with a J valve.

(BTW: Herman, if you need a extra J valve or 2 let me know, sorry, no actuating rods)

 

[Couv]

Checking the position of the valve is every bit as easy as checking a SPG. Having said that, I'll admit J valves aren't for everyone and should only be rented and used by divers familiar with them. If one must rent a J valve and is uncomfortable/not familiar with them, it is best just to leave it in the reserve position and dive it as though it is a K valve.

c

 

[*dave*]

Most J Valves I've seen in the last six years have been disabled and the lever does nothing.

 

[spectrum]

There is a big difference between a vintage equipment diver (even if it's only the old valve) enjoying one of these and some Joe Diver that just got this odd valve on CraigsList, eBay or at the local flea market.

They have a use and they need to be understood. Mistakes happen and the informed user knows that.

Pete