User avatar
SurfLung
Master Diver
Posts: 1280
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Proper J-Valve Function

Mon Aug 20, 2018 4:55 pm

Proper J-Valve Function
- I try to run out of air with my J-Valves at least once a year to make sure they are functioning properly. 3 weekends ago, I dove one set of Twin 38s that I had been servicing and thought I had a properly working J-Valve on but instead, the reserve leaked past the J-Valve and I breathed the tanks right down to zero. When I got home, I tested it by letting the air out with the J-Valve on and it just leaked everything out past the valve.
- So LAST weekend I tried diving with two other Twin 38s that I knew had properly functioning J-Valves. The first one worked perfectly: I breathed it down to a hard draw, pulled the lever, heard the air balance between the two tanks, and I breathed easy for at least 5 minutes more.
- But the second set just kept giving me air until I gave up waiting for the reserve and ended the dive. When I pulled the lever up by the car, I could hear the tanks balancing but only briefly. And when I checked the pressure, it barely moved to 100 psi. Now, this set I have breathed down to a hard suck and actuated the reserve successful on several occasions. So I filled it up past 500, flipped the reserve up and opened the valve to empty the tanks. It emptied down to a slow leak but it never totally stopped. And once again when I pulled the lever, the tank balancing sound was very short and the measured pressure was barely 100 psi.
- Now, I've had twin tanks that I thought were empty until I pulled the reserve lever... The reserve was sealed that perfectly. But I've also been told that they're supposed to leak a little since they're only held closed by a spring... Which your breathing can overcome somewhat.
- I would prefer these things to seal the reserve air with no leaks until I need it. My question is whether this is proper and possible and second where can I get new seats and springs?
Image
P.S. I looked in my Basic Scuba book and there is a difference in the reserve mechanism of the old 1/2 NPT threaded manifolds and the new 3/4 manifolds. The springs have the same part number but the seat is called a flow check on one and a disk and something on the other... With different part numbers.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

User avatar
antique diver
Master Diver
Posts: 1693
Joined: Sun Dec 10, 2006 12:50 pm
First Name: Bill
Location: North-Central Texas

Re: Proper J-Valve Function

Mon Aug 20, 2018 10:00 pm

I see a lot of variation in my J's too. Enough that it's hard to trust them. Probably just need new reserve seats, but I don't know of a source. I think I am down to having only one new one left.
"I get plenty of excercise just pushing my luck!"

User avatar
ScubaLawyer
Master Diver
Posts: 1095
Joined: Thu Apr 08, 2010 11:25 am
First Name: Mark
Location: Laguna Beach, CA

Re: Proper J-Valve Function

Mon Aug 20, 2018 10:27 pm

I always try to see where the J is gonna kick in by watching my spg at the end of every non-vintage dive. Same J-60 will kick in at any where from 400 to 200 psi so not sure what accounts for the variation on the exact same valve.
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968) :D

User avatar
SurfLung
Master Diver
Posts: 1280
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Re: Proper J-Valve Function

Tue Aug 21, 2018 9:39 am

Inconsistent Springs?
- I've had the old J-Valves apart on both single and double tanks and the springs look identical even though they are supposed to be rated 300 and 500 psi. I just wonder how often they might have got mixed up. You put the 300 on a double tank and after decanting, the 150 psi in each tank ,might not even register on a pressure gauge. I'm thinking that springs that light (and old) might actually be marginal in their consistency... That is, one might be strong enough to seal completely and the next might be weak enough to leak a little but still work in a diving situation where demand is constant and there is no time for the reserve to leak out before it gets used. I'd rather it sealed completely.
- XS Scuba has introduced modern J-Valves for single tanks that are set for 600 psi... A stronger spring to seal better and higher psi to fit the modern practice of ending a dive when air gets down to 500 psi. I couldn't find the spec for their Thermo twin tank manifold J-valve.
- Anyway, I'm going to see if I can find some stronger springs of the same dimension and see if that gives a better seal.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

User avatar
SurfLung
Master Diver
Posts: 1280
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Re: Proper J-Valve Function

Fri Aug 24, 2018 9:27 am

It's the Seats that leak...
- I took this seat from a J-Valve that leaks but DOES work (marginally). That is, it will restrict breathing when air pressure gets low and will give you good breathing when you pull the lever. But for how long is anybody's guess. As you can see from the photo, its understandable why it leaks.
JValve01.jpg
- I used a nylon tooth brush and simple green to clean up this seat but what was underneath wasn't much better. And the J-valve function didn't improve much after the clean up. The metal orifice that the seat seals was pitted lightly, too. So, what can be done?
- If you look closely you will see that the seat has been crimped in place... Part of the crimp is actually broke off. I take it this crimp is to keep the seat from coming loose and jamming the airway in the valve. So, replacing the seat with a washer of new material may not be an option. But I can see where a lathe could turn down the crimp ridge and if a new seat could be secured reliably without a crimp, maybe a new seat could work.
- I'm also thinking of ways to re-face the existing seat... Like we do with the HP seats on Mistrals and DAAMs. Perhaps a piece of straight metal tubing with the end turned nice and flat to fit over the pin and smooth the seat with an abrasive?
- Could a new seat be made from some existing part... Such as a valve seat with a pin installed in the middle?
You do not have the required permissions to view the files attached to this post.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

User avatar
captain
Plank Owner
Posts: 1323
Joined: Mon Jul 04, 2005 11:32 am
Location: LaPlace, LA

Re: Proper J-Valve Function

Fri Aug 24, 2018 10:14 am

I have a small number of NOS seats available, PM me.
Captain

User avatar
SurfLung
Master Diver
Posts: 1280
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Re: Proper J-Valve Function

Fri Aug 24, 2018 5:11 pm

PM Sent... Thanks for responding Tom.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

User avatar
captain
Plank Owner
Posts: 1323
Joined: Mon Jul 04, 2005 11:32 am
Location: LaPlace, LA

Re: Proper J-Valve Function

Sat Aug 25, 2018 10:03 am

Eben, I received your PM but my reply does not leave my out box. I sent you a email to your email address.
Captain

User avatar
SurfLung
Master Diver
Posts: 1280
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Re: Proper J-Valve Function

Mon Aug 27, 2018 9:30 am

captain wrote:
Sat Aug 25, 2018 10:03 am
Eben, I received your PM but my reply does not leave my out box. I sent you a email to your email address.
Thanks Tom, I got the email and sent payment by paypal this morning.


Basic Scuba on J-Valves

- I finally thought to look things up in Basic Scuba and I got some very clear information. Apparently, it is normal for a J-Valve to leak. In fact, the whole time you are diving with tank pressure over 300 psi, the air you breathe is leaking past the J-Valve because the higher pressure can overcome the J-Valve spring that holds the seat closed. It is only when the tank pressure gets down in the 300 psi range that the J-Valve spring is able to "restrict" the air flow. This restriction is supposed to be dramatically noticeable by the diver, so that he knows he is almost out of air and begins to surface. If the diver is breathing hard, he will probably notice the restriction sooner than if he is breathing easy. Pulling the J-Valve physically opens the J-Valve seat, compressing the spring and giving the diver un-restricted access to the remaining air in the tank.
- There are a number of factors affecting exactly how much air pressure is held in reserve. Here are the two main ones. First is the spring... Basic Scuba says the springs can vary +/- 100 psi. So a 300 psi single tank reserve might give you as much as 400 psi or as little as 200 psi. Second is the condition of the seat. Dirty, corroded, or degraded by age may leak enough not to restrict the air flow at all. Or, only when you're breathing hard.
- Ambient Pressure plays a role, too. This is kind of interesting. If I understand it right, the reserve valve delivers more air when you are deeper and less air when you are shallow. This is because the force of the air restriction is actually the power of the spring plus the power of the ambient air pressure. In the example given in the Basic Scuba book, the reserve restricted at 300 psi spring + 44 psi ambient = 344 psi. Simply brilliant. For this reason and the never-completely-sealed aspect, and the depends on how hard you're breathing aspect... I don't think it's reliable to try and measure the reserve pressure with a tank checker nor an SPG. I've tried it and it made at least one J-valve look like it wasn't working when it was. The confirmation you seek is a moving target.
- I think the bottom line in using a J-Valve reserve regularly is to physically test it out by breathing it. Breathe your tank(s) down to nothing and see if the reserve actually gives you sufficient air to finish your dive. This isn't hard to do if you have a tank balancing hose. Simply fill the J-valve test tank from a full tank. Fill it to 350 psi and lift the reserve lever to "On". Hook up a regulator and start breathing until you feel a significant restriction. Breathe hard and soft so you can see the difference it makes. Then, flip the reserve lever down and start a stop watch. Now breathe through the regulator until the tank is empty and the stop watch will tell you how much time your reserve will give you.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

Return to “Tanks and Valves”

Who is online

Users browsing this forum: No registered users and 1 guest