K-Valve on Steel

[G-lock]

I've seen a few folks mention that they would not use a K-valve on a steel tank, why not? I am considering a PST E-7 100 and thought the DIN/K valve would be neat since my MK25 is a yoke. I know it's convertible but I intend to travel alot so I thought this would save the hassle of converting it back and forth. Thanx in advance! Jeff

 

[Rick Murchison]

There are a couple of issues in this question.
First of all, the E7 tanks are, I believe, HP tanks and should be fitted with 300 bar DIN valves only.
The convertable K/DIN valves are 200 bar DIN and only suitable for LP steels - and only then if you intend to operate those tanks as LP's.
The principle objection to K's on steel is most likely due to folks routinely filling them to pressures inappropriate to the K/Yoke or 200 bar DIN connection.
Personally I use 200 bar DIN/yoke convertables on LP steels and keep the pressure low.
Rick

 

[G-lock]

Rick-
Thanx for the reply. Insightful as always. I was thinking along the same lines. The new E7/8's are 3442 PSI and use a combo valve. I checked the specs on my MK25 and in the yoke config it's rated for 232Bar/3442 PSI, so it looks like PST is taking the yoke to it's maximum level. This however seems to fit the bill for what I want in an HP 100, I fel it would give me the flexibility for more gas when warranted. Jeff

 

[Bob3]

Just to keep the terminology correct, a K valve can be either DIN or yoke, unless it's got the built in reserve, in which case it'd be a J valve.
The terminology is a carry over from the 1953 US Divers catalog where the reserve valve is item J and the non-reserve was item K.
DIN valves were in use in Europe by the mid-late '50s, with pressures running up to 4400 psi.
Rick's right about the pressure differences between the 200 & 300 bar tanks, plus the 300 bar valve heads are deeper so the screw in yoke adaptor won't seat, even if someone files out the inside of their yoke to get it over the deeper head of the 300.

Take a peek at the "oldest dive catalog": http://www.geocities.com/athens/atlantis/2427/divecat/index.html

 

[LUBOLD8431]

Well, the DOT does not require the use of a DIN with pressure of 3442.
So, the PST cylinders are safe with the use of a yoke valve.
I think this is precisely why PST did this, so that more people can use these cylinders with a yoke connection.

Now, is it safe to use the 200 bar DIN connection on the cylinder with a DIN regulator.

The answer is YES... Strength, safety, compatibility all are NON issues here. 200 bar DIN is safe to use with that pressure.

All that being said, yes, some people will change the cylinder valve out to a 300 bar DIN.

 

[G-lock]

So shouldn't the combo valve truly be listed as ~240 bar/3442 psi valve? Jeff

 

[Rick Murchison]

LUBOLD8431 once bubbled...
The answer is YES... Strength, safety, compatibility all are NON issues here. 200 bar DIN is safe to use with that pressure.

Can you cite the authority for that? I haven't ever seen that in writing from a reputable source.
Would appreciate it.
Thanks,
Rick

 

[LUBOLD8431]

Ummm, yeah, THERMO and PST...

I dont have anything on paper or a website, but let me get back to you... I am goin to call them today...

 

[metridium]

G-lock wrote...
I've seen a few folks mention that they would not use a K-valve on a steel tank, why not?

Two reasons I wouldn't use a standard convertible K-valve on a steel tank:

1. Since I would use steels only for back tanks, I'd either install an H-valve or double them up with a manifold. A K-valve supports only one first stage, which is fine for many people, but something I prefer to avoid.

2. I wouldn't use a convertible valve because that lessens the likelihood of some yahoo picking up one of my tanks by mistake and possibly taking it past its MOD, stickers notwithstanding. 300 bar regs still aren't that common among the general populace.

 

[pescador775]

It's OK to use a yoke style K valve on a high pressure tank up to 4000 psi. In the 1970's, US Divers rated their yokes at 4000 psi working with failure limit of 10,000 psi, and this is the same yoke in production today. Personally, I set 3500 as the working press (my compressor relief valve won't go any higher). Look closely at a modern yoke, especially Scubapro and USD; these are strong enough to use as a trailer hitch. Don't worry about that. It will never break due to tank pressure. If the valve is new or otherwise in good condition and the O ring is the white, hard silicone type, the ring will never blow out. You see, also in the 1970's, coincident with the yoke redesign, Sherwood Co. completely redesigned the valve annulus which seats the O ring. That interface is no longer a compression fit where the ring acts as a washer. The fit is a 'semi captured' design which makes metal to metal contact between the regulator and valve face. The O ring CAN NOT BLOW OUT unless the annulus has been icepick challenged. Relax and don't pay any attention to all the reasoned 'arguments'. I've been there done that.