When do you change an O-ring (if the yoke's on you)?

[pescador775]

I can't offer much here. Luis has it right and I agree with clayjar that rotted O rings can cause a nasty surprise. Also, I've seen a couple of negative posts about the "purple" O rings. I've never used them but wonder about using them for valve face applications. Maybe they are too soft to be used in a compression fit. The DIN connection is a nice design and would be excellent in a laboratory or factory setting. For use in the field, it is necessary to keep the socket very clean, no sand or salt, and for compressor operators, be alert for water inside. Yoke and DIN valves are always subject to being knocked about. Damage to the yoke valve can often be traced to clumsy slip ups during maintenance. The DIN is a thin wall brass casting which should be protected from dents or distortion. WRT regulators, the DIN inlet is not protected by a yoke so cap it off when not in service. The yoke regulator inlet face is subject to being scratched while sliding the regulator on the valve. However, it takes a lot of abuse to cause a leak.

 

[Leadking]

Also, I've seen a couple of negative posts about the "purple" O rings. I've never used them but wonder about using them for valve face applications. Maybe they are too soft to be used in a compression fit.

Thermo used the EPDM (purple) o-ring for oxygen compatability. The issues encountered were not due to the the properties of the material (although it does tend to extrude through a smaller opening) but that the yokes offered on many regulators stretch under pressure to create the opening. Due to the design of the yokes AND not the properties of EPDM it was decided to use Viton.

We had a customer, who is well known to this group, complain about EPDM and when we got down to the root cause of extrusions it turned out to be worn out fill adapters. When new fill whips were used the problem went away.

Lee
www.seapearls.com

 

[CBulla]

Hmm.. I use my gear so often than when the o-ring looks ratty (usually when using other fill stations than the local shop I work at, they seem to crank the yoke down in some east FL stores) I turn it about and when it looks a bit flat I just change it out. I've noticed the viton rings are more susceptible to wiggling in their seat than the rubber ones, and take considerably more use before showing wear. The rubber O-rings I'd have to change about every 8 or so fills.

 

[pescador775]

Oh, great, thanks, guys. I knew someone would throw me a bone.

Torquing down the yoke has no detrimental effect on the O ring because the yoke inlet and the valve face make metal to metal contact which limits the compression of the O ring.

The yoke "stretch" thing is still being floated as a straw man. There are two ways of measuring this, one method is called "expansion" and the other "stretch". Measuring the distance from the yoke to the valve is "expansion" and varies with the amount of pressure put on the yoke screw, IOW, how firmly is the screw turned down. It is pretty useless, IMO. The other method is called "stretch" and measures the actual elongation of the brass yoke. My measurements of stretch show that a yoke manufactured in 1955 had temporary elongation of 0.007 at 3500 psi, and was commonly used by the navy at pressures up to 3000 psi without problems even though the rated service pressure was more like 2500 psi. Measurements of modern yokes mfgt by US Divers and Scubapro showed 0.002-003 elongation. In other words, the modern yokes were 2-3 times as strong as the old yoke. My conclusions: the modern yoke is reliable to 4000 psi provided the correct O ring is used. If you bought something with a wimpy yoke, do not use above 3000 psi. If you don't tighten the yoke screw and something leaks, it presents a perfect opportunity to dump your complaints on Scubaboard.

 

[Leadking]

If you have a properly rated yoke and screw it down properly the o-ring can't extrude, it's got nowhere to go!

 

[jmps]

We were sitting in the cabin of the dive boat last weekend when POW HISSSSSSSS on one of the guys tanks HP 3442 yoke tanks. That was the first time I heard one blow. I bought a couple of spares today. Luckily the boat has a compresssor.