Just exactly how many o-rings needed when attaching 2nd-stage to LP hose ?

[scubafanatic]

When attaching a 2nd-stage to a standard LP hose, I know there's a small somewhat hidden' O-ring within the LP hose fitting, it's size = '010' I believe. However, are there any additional o-rings that need to be included when attaching a 2nd stage to it's corresponding standard LP hose ?
The Vance Harlow 'SCUBA Regulator Maintainance and Repair' manual doesn't mention any other o-rings, but it appears I could (or even should) be installing a 2nd o-ring by sliding perhaps a '013' sized o-ring over the male threaded part of the 2nd stage, which would then be 'sealed' when I screw on the LP hose to the 2nd-stage. Should I be installing this 'second' o-ring, and if 'yes', what size.....'013' or something else ? If the answer is 'no', would the 'no' be because it's overkill and not really needed, or would installing such a second o-ring be a genuinely bad idea ?

Thanks in advance,

Karl

 

[Scared Silly]

Single o-ring in the LP hose is standard as it is captured between the "nipple" of the hose and the inside of the inlet tube. The second o-ring over the inlet tube has been used as well. I seen it for example on Atomic's comfort swivel hose which has a grove for it to sit in.

The reason for the single o-ring via the hose nipple is because most regulars have a jam nut that goes on the inlet tube before the hose. As such an o-ring over the inlet tube would not seal the hose.

 

[scubafanatic]

Single o-ring in the LP hose is standard as it is captured between the "nipple" of the hose and the inside of the inlet tube. The second o-ring over the inlet tube has been used as well. I seen it for example on Atomic's comfort swivel hose which has a grove for it to sit in.

The reason for the single o-ring via the hose nipple is because most regulars have a jam nut that goes on the inlet tube before the hose. As such an o-ring over the inlet tube would not seal the hose.

Thanks Scared Silly! I hadn't ever noticed such a 2nd o-ring and while I was installing a Universal Swivel Hose (Atomic) on a 'new to me' Scubapro 109/156 BA 2nd-stage it got me to wondering if I'd been missing a 2nd o-ring on all my other reg sets or not. It almost seems sea water could get inside the 'swivel' area without such a secondary o-ring, especially as I'm using the 'universal' Atomic swivel, and not the one designed specifically for Atomic regs. My SP 2nd stage doesn't have that special groove over the 2nd stage inlet tube, but there is a little space there the inlet tube threads stop, a small smooth space where an o-ring could rest, it I wanted to put one there.
So it sounds like, strictly speaking, it's not common practive to use such a second o-ring, but there are exceptions like Atomic.
I amlost wonder what would happen IF I tried it out anyway ? If I tried it as a 'test', pressurized the reg, and no leaks or other signs of distress, would you consider it safe to dive ? (that theoretical second o-ring would be pretty thin, especially after I tighten the connection) so it's hard to see how it would introduce enough slack/space to cause the 'inner' o-ring to not seal properly anymore. Is that a crazy thought ?

 

[redacted]

I have seen the 013 in a scubapro schematic - I believe it was for a G500. It obviously does not seal anything. I decided it must serves as a cushion between the jam nut and the case. I do install them when the jam nut tightens directly against the (plastic) case. It is a bit easier to control the torque without risking case damage.

 

[scubafanatic]

I have seen the 013 in a scubapro schematic - I believe it was for a G500. It obviously does not seal anything. I decided it must serves as a cushion between the jam nut and the case. I do install them when the jam nut tightens directly against the (plastic) case. It is a bit easier to control the torque without risking case damage.

I hadn't thought of using the o-ring merely as a sort of 'cushion' only. Makes sense in that application.

 

[axxel57]

I'm sure awap is right, this o-ring is only used as a puffer to be able to torque softly without risking to loosen the jam nut while using it.

To my opinion it fulfills the same work as the tiny 363 o-ring in the D -Series poppets.

The size of the 347 is actually 014 - 90 Buna.

 

[Luis H]

I agree that this sounds like a locking device. Similar to a a nylon locking nut, but even softer. You can just hand tighten the hose nut without fear of it coming loose when it swivels.

 

[Nemrod]

I have installed O-rings into LP female fittings for years. It simply serves as a locking agent. I usually only run my fittings finger tight in that area. It does not work with some fittings.

N