Spare Air – The Best Item in Your Scuba Toolbox

[boulderjohn]

The most interesting part is the name J and K valves never appeared in the catalog. The name came from the item numbers in the 1953 price list. It also shows why the reserve/J-valves were in the minority. Everyone knew they didn't work that reliably and they were over 3x the cost.

Show the whole page and look at the three items below the Self contained diving booklet..

 

[Akimbo]

Show the whole page and look at the three items below the Self contained diving booklet...

I saw that but it only appears in the price list referring to the item letters, as near as I can tell. I always found it surprising that after years of all their customers (dive shops) still calling it J and K valves that it never showed in up in LDS/consumer catalogs. I remember asking my dive instructor in 1962 why they call it J&K valves and he didn't know. Strange how language evolves.

 

[agilis]

The most interesting part is the name J and K valves never appeared in the catalog. The name came from the item numbers in the 1953 price list. It also shows why the reserve/J-valves were in the minority. Everyone knew they didn't work that reliably and they were over 3x the cost.

Apart from the possibility of having the J valve reserve activated without the diver being aware that the pull rod was in the down position and that consequently no reserve existed when breathing became difficult, was there any reliability issue, any mechanical problem or weakness?

I used J valves for many years from my earliest dives (and was aware of the 'J' 'K' catalog designation origin of the terms) and never heard about any reliability problems, other than those that arose from the diver's failure to check the position of pull rod activator frequently. They were more expensive, but without an SPG, which very few people knew existed many decades ago, the safety factor was compelling.

 

[Akimbo]

Apart from the possibility of having the reserve activated without the diver being aware that the pull rod was in the down position and that consequently no reserve existed when breathing became difficult, was there any reliability issue, any mechanical problem or weakness?...

Yes, the non-adjustable activation pressure was a big problem. The design range is usually specified as 300-500 PSI, but tests on slightly worn valves showed it could be as low as 200 PSI. That is no reserve at all considering the poor performance of regulators of the day at low supply pressures.

It gets worse. The vast majority of cylinders in the late 1950s were single 72s (71.2 Ft³) at 2250 PSI. The usable reserve even at 300 PSI wasn’t much considering what you could actually suck through a regulator. Regulators of the day were often breathing hard even after J-valves that kicked-in at 300 PSI were opened. It didn’t take long for most people to figure out that they weren’t worth 3x the price or the added maintenance.

Yes, the “perceived” safety factor was compelling. I understand that the majority of the first cylinders purchased by divers were J-valves and most subsequent cylinders had K-valves. The breathing resistance increase at low supply-pressures was the reason SPGs weren’t considered all that valuable. They were definitely available. See: http://www.scubaboard.com/forums/ad...ns/476204-submersible-pressure-gauge-spg.html

It was really useless on surplus twin 38’s at 1800 PSI. The J-valve only held back pressure on one of the cylinders. You could hear the cylinders equalizing when the lever was opened. The J-valve on the triple 44’s at 1800 PSI from the mid-1950s was completely useless. The actual reserve starts making a spare-air look good. It is also why Cousteau’s rigs all held a full cylinder in reserve.

 

[Crush]

Love this thread! Thanks to the OP for starting a spare air thread. I'm gonna start a jacket vs BP&W thread next, or maybe deep air...

 

[agilis]

Interesting. Thank you. I remember that the last J valves I used in the late 60s were Dacor. Because I already had them I used my J valve tanks with my first SPG in the early 70s. The valve reserve invariably kicked in between 500 and 600 psi. I still have one mounted on a big unwieldly orange 100cf (@2700 psi) aluminum tank that I have not used in 40 years. I wonder if it can be removed. I'd like to see how it performs.

I wonder what it is in the valve that becomes slightly worn. Perhaps the spring weakens? In any case, it sounds like it becomes the equivalent of a K valve, or close.

 

[Akimbo]

… I wonder what it is in the valve that becomes slightly worn. Perhaps the spring weakens?...

There was a lot of manufacturing variation to start with, often above and below the 300-500 PSI spec. I was pretty young and gave up on J-valves before learning to rebuild valves or regulators. Guys in the Vintage Forum are more up on the nuts & bolts. Like you, my first guess would be the stainless spring is the major culprit.

 

[supergaijin]

Unfortunately Spare Air is marketed towards beginners as a good diving/buddy substitute. Many divers however also become lax on buddy protocol and or are diving solo/photo (same thing IME). Again for the experienced diver, I believe it is enough to surface at a slower rate than one could achieve with a CESA. My SAC has never approached 1cbf/min in years. My typical SAC is 0.25cbf/min.

I would never take a Spare Air as an alternative to a good buddy/pony on dives to 4ata, but for dollying around on a typical 3ata dive, I would not have a problem. Personally I think slinging a small pony is a PITA.

 

[akdeepdiver]

Love this thread! Thanks to the OP for starting a spare air thread. I'm gonna start a jacket vs BP&W thread next, or maybe deep air...

Combine it all. Deep spare air while wearing a horse collar BC.

 

[boulderjohn]

The actual reserve starts making a spare-air look good.

Never having used a J-valve, I found this whole discussion enlightening. I was thinking exactly what you wrote here when I was reading.