J Valve

[scubadada]

All 6 of my tanks have J valves. One other benefit a of J valve is it is a better carrying handle than a K valve.
In my experience I have never had a steel 2450 psi 72 get me anywhere near the no deco limit on the old Navy tables on the first dive.

Your dives must be shallower than the ones I did on my steel 72s on air. I routinely approached NDL on any dive below 60 ft. These were using the USN tables 1970-1972 Quiz - Recreational Dive Planner - Exceeds NDL By 6 Minutes

 

[AfterDark]

Your dives must be shallower than the ones I did on my steel 72s on air. I routinely approached NDL on any dive below 60 ft. These were using the USN tables 1970-1972 Quiz - Recreational Dive Planner - Exceeds NDL By 6 Minutes

My 72s are rated 2250 no way with my sac rate which has never been good, I'd ever get near an NDL at any depth. I can't even get close these days with my 96 at 3000 psi. With my 72 IDs I have to watch it.

These are from an old US Navy Manual

 

[scubadada]

Hi @AfterDark

I see your old graphs show RMV in LPM. For the last 1450 dives, my average RMV is 10.2 LPM, it wasn't much higher back in the day. The graphs start at 18 LPM

Take care, stay healthy, Craig

 

[AfterDark]

Hi @AfterDark

I see your old graphs show RMV in LPM. For the last 1450 dives, my average RMV is 10.2 LPM, it wasn't much higher back in the day. The graphs start at 18 LPM

Take care, stay healthy, Craig

Well that splains it.

 

[John C. Ratliff]

My 72s are rated 2250 no way with my sac rate which has never been good, I'd ever get near an NDL at any depth. I can't even get close these days with my 96 at 3000 psi. With my 72 IDs I have to watch it.

These are from an old US Navy Manual View attachment 580711

I'd like to point out that these Navy tables assume a 500 psig spring on a single 72 cubic foot tank, and go from 2250 psig to 500 psig. But single 72 valves in the USA had a spring set to 300 psig. Also, they were only a 72 cubic foot tank when the pressure started at 2475 psig, the 10% overfill. At 2250 psig, these tanks hold 65.5 cubic feet of air (rounded to 66 ft3).

SeaRat

 

[AfterDark]

I'd like to point out that these Navy tables assume a 500 psig spring or a single 72 cubic foot tank, and go from 2250 psig to 500 psig. But single 72 valves in the USA had a spring set to 300 psig. Also, they were only a 72 cubic foot tank when the pressure started at 2475 psig, the 10% overfill. At 2250 psig, these tanks hold 65.5 cubic feet of air (rounded to 66 ft3).

SeaRat

Still close enough for govt. work.

 

[vjb.knife]

All the J-valves used here in Italy, both the spring-loaded Technisub model, and the normal Cressi or Mares ones, were always designed to be on the side close to your back, not external as I see in some of your photos.
Now I understand why with American valves it was so easy to open the valve inadvertently...

This is a good point especially if diving in a lot of debris or kelp. The lever should be configured toward the body, which gives it less chance to snag on something. I stated diving in 1970 and had a tank with a Scubapro J-Valve. This is the J Valve that had two pressure reserve settings. I still own it but do not use it.
In 1976 I finished Commercial Diving School at SBCC in California and used it when SCUBA Diving back then but at that time we were not even using bail-out bottles when diving surface supplied gas or bell diving including saturation. later in the early 80's we were using them. Shortly after that I quit diving and went back to school for an Engineering degree. I did non-diving work in Engineering and other fields until 3 years ago. I moved to Hawaii and now work for a Submarine company as the lead diver where we use SCUBA. Per OSHA and company policy all of our tanks have J-Valves on them. We are required to have them or a bailout bottle with a second regulator, or a spare air. So we use the J-Valves. This is exceptionally stupid in my opinion for a slew of reasons. First we keep them in the down position which makes them essentially k-valves. Next all regulators have SPGs on them. Also, about 99% of our work is done in 25 feet of water or less. Lastly it becoming harder and harder to get the J-Valves that we have serviced. they are several different brands and parts are getting very scarce for some of them.
The bottom line is that J-Valves are worthless and should never be relied on as a means of reserve breathing supply, which is one reason that we leave them in the down position at all times.

The reason that the one commercially available J-Valve costs $499 is simple; supply and demand. There is virtually no demand for them.

 

[Angelo Farina]

This is a good point especially if diving in a lot of debris or kelp. The lever should be configured toward the body, which gives it less chance to snag on something. I stated diving in 1970 and had a tank with a Scubapro J-Valve. This is the J Valve that had two pressure reserve settings. I still own it but do not use it.
In 1976 I finished Commercial Diving School at SBCC in California and used it when SCUBA Diving back then but at that time we were not even using bail-out bottles when diving surface supplied gas or bell diving including saturation. later in the early 80's we were using them. Shortly after that I quit diving and went back to school for an Engineering degree. I did non-diving work in Engineering and other fields until 3 years ago. I moved to Hawaii and now work for a Submarine company as the lead diver where we use SCUBA. Per OSHA and company policy all of our tanks have J-Valves on them. We are required to have them or a bailout bottle with a second regulator, or a spare air. So we use the J-Valves. This is exceptionally stupid in my opinion for a slew of reasons. First we keep them in the down position which makes them essentially k-valves. Next all regulators have SPGs on them. Also, about 99% of our work is done in 25 feet of water or less. Lastly it becoming harder and harder to get the J-Valves that we have serviced. they are several different brands and parts are getting very scarce for some of them.
The bottom line is that J-Valves are worthless and should never be relied on as a means of reserve breathing supply, which is one reason that we leave them in the down position at all times.

The reason that the one commercially available J-Valve costs $499 is simple; supply and demand. There is virtually no demand for them.

Really a pity that those excellent Technisub valves are not anymore available. They were truly safe, as it was impossible to pull them down by error. Above the action pressure, they did simply come up again thanks to the spring...

 

[John C. Ratliff]

Really a pity that those excellent Technisub valves are not anymore available. They were truly safe, as it was impossible to pull them down by error. Above the action pressure, they did simply come up again thanks to the spring...

Angelo,

Would it be possible to see a parts diagram of the Technisub J-valve and J-valve manifold for twin tanks? I'd like to see this design.

SeaRat

 

[John C. Ratliff]

Here is an example of when a J-valve should not be used, at all:

IMG_2796 by John Ratliff, on Flickr
This is a Dacor Nautilus Constant Volume System (CVS) that I have been using for a few years. Note that the J-valve is down, and not functioning. This is because the J-valve in this unit cannot even be reached, over the shoulder or via a pull rod.

IMG_1042 by John Ratliff, on Flickr
Here is a J-valve manifold on a triple tank unit (at Laura Hanna's Pacific Watersports in Aloha, Oregon; she has quite a collection of old dive equipment). The reserve spring is set at 750 psig, and equalizes into the other two cylinders. This unit dates back to the early 1960s.

IMG_0007 by John Ratliff, on Flickr
Here is a J-valve built into a Sportsways Sport Diver regulator. This way, it can be used on either a K-valve or a J-valve tank. It can also be used in the center of a double tank system, and holds back 300 psig in both tanks (better than the 500 psig in one cylinder on a J-manifold, as that equalizes to 250 psig when tripped).

IMG_1009 by John Ratliff, on Flickr
This is the Scubapro adjustable J-valve, which has a spring which can be set to either 300 psig or, when that center screw is depressed, to 600 psig. The regulator first stage is a Healthways Scubair regulator (the original tilt valve and first stage with a diaphragm regulator).

IMG_8668 by John Ratliff, on Flickr
This is how the J-valve was designed to be used, with a single hose regulator or a double hose without a SPG.

That's enough for now. I'll have more to say about my experiences with the J-valve, which I still use, later.

SeaRat