Anyone using '013' O-rings as mating surfaces for more 'grip' when attaching 2nd stage to LP hose ?

[Akimbo]

O-rings are designed to move in the gland or groove and should not be part of the thread-locking method. This thread may help explain it: O-rings for Divers

 

[tbone1004]

@Akimbo that's why omniswivel calls them vibration dampening o-rings or something. I definitely find that they act somewhat like a lock washer to keep them from getting loose

 

[kelemvor]

Huh.. I didn't know you could do it without an o-ring. Everything I've got has an o-ring there that either came with the second stage or was installed by some tech.

 

[Akimbo]

that's why omniswivel calls them vibration dampening o-rings or something.

O-rings by nature will dampen vibration, but that is different than using them as a torque limiter. The OP is asking about using an oversize O-ring for this purpose. The problem with using an oversize O-ring in an SAE Straight Thread Boss is mechanically over compressing the material can initiate deformation that leads to extrusion failures.

Edit: This was written more for other readers, tbone knows this stuff already.

 

[scubafanatic]

Huh.. I didn't know you could do it without an o-ring. Everything I've got has an o-ring there that either came with the second stage or was installed by some tech.

Interesting observation. While my experience has been the opposite, your experience would indicate it's perfectly reasonable to go ahead and install them if one wanted to.

 

[scubafanatic]

O-rings by nature will dampen vibration, but that is different than using them as a torque limiter. The OP is asking about using an oversize O-ring for this purpose. The problem with using an oversize O-ring in an SAE Straight Thread Boss is mechanically over compressing the material can initiate deformation that leads to extrusion failures.

Edit: This was written more for other readers, tbone knows this stuff already.

From what I can tell so far, the O-rings are being somewhat squeezed as you say, but it appears very symmetrical in nature and I'm not squeezing them down to the max, but you state a legitimate concern, so I'm still thinking about what I should do here.

 

[Akimbo]

By design, "locking" SAE J1926 straight thread bosses should come from the metal to metal contact/friction caused by proper torquing of the threads instead of any torque limiting contributed by the O-ring. Could it be that you are not tightening the connection enough? The connection should be lightly torgued, but just enough that it doesn't unscrew or back off in use.

I don't recall the proper torque for this connection, but @couv or @herman probably do.

 

[JackD342]

I've been installing '013' Viton O-rings when attaching 2nd stages to LP hoses, I feel this provides more 'grip' to prevent unwanted unscrewing/rotation from accidentally having those components separate, and is a better idea than just having raw chromed brass surfaces as the mating surface.

Anyone else do this or feel it's a good or bad idea ?

Thanks!

I have been holding off to see what others have to say, but it seems like the spectrum has been pretty much covered with no consensus. I can't provide any technical justification, but my gut says that adding O-rings between the 2nd stage connector and the LP hose is a bad idea. Might be better than a poorly tightened connection, but I would be worried that it comes apart more easily than a properly tightened connection. (@Akimbo - I checked one service manual for one brand, and that one said 40 in-lbs. Yes, hoses connections I tighten by feel and not with a torque wrench)

You seem to have experienced a very unusual situation where significant, sustained vibrations that loosened the connection, but it also could be those vibrations were enough to loosen a poorly tightened connection.

If I thought I really had a problem with that particular connection, my first thought for a non-standard fix would be to consider adding a drop of two of Loctite Thread Locker 242 to the threads. I already use that, per MFGR instructions, on some 1st stage yoke connectors. Disclaimer: Do NOT interpret that as having said it is recommended for 2nd stage connections.

 

[scubafanatic]

I have been holding off to see what others have to say, but it seems like the spectrum has been pretty much covered with no consensus. I can't provide any technical justification, but my gut says that adding O-rings between the 2nd stage connector and the LP hose is a bad idea. Might be better than a poorly tightened connection, but I would be worried that it comes apart more easily than a properly tightened connection. (@Akimbo - I checked one service manual for one brand, and that one said 40 in-lbs. Yes, hoses connections I tighten by feel and not with a torque wrench)

You seem to have experienced a very unusual situation where significant, sustained vibrations that loosened the connection, but it also could be those vibrations were enough to loosen a poorly tightened connection.

If I thought I really had a problem with that particular connection, my first thought for a non-standard fix would be to consider adding a drop of two of Loctite Thread Locker 242 to the threads. I already use that, per MFGR instructions, on some 1st stage yoke connectors. Disclaimer: Do NOT interpret that as having said it is recommended for 2nd stage connections.

Why recommend for 1st stage connections but not for 2nd stage connections ?

 

[JackD342]

Why recommend for 1st stage connections but not for 2nd stage connections ?

To expand on my point, my use on some 1st stages is per that particular MFGR's specific service instructions, not something I came up with on my own. My first reaction on reading that was "I need to do what!?!? Is that really necessary?" But I went out and bought the tube of Loctite and use it every time, when/as directed, no more and no less.