scubatoys:
Hmm I need to check into this a little more. BTW did you see the note to the 75 ft lb setting. It appears to apply mostly to SCBA tanks. Not sure though why that in and of itself would make a difference.
Vip +
- Thread starter silverbackmrb
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
Hmm I need to check into this a little more. BTW did you see the note to the 75 ft lb setting. It appears to apply mostly to SCBA tanks. Not sure though why that in and of itself would make a difference.
Scubatoys and Ontario Diver---the question becomes, the thump from whos hand is the correct thump. I have been a bystander observing how much force someone has had to use to get a valve broke free with a wrench. I've also seen situations where the person removing the valve had to hit it a couple of times and were surprised at how hard they had to hit it to break it free. I have even seen a mallet used to both tighten and loosen a valve.
While I understand and don't doubt that you understand what you are doing(clearly indicated above), conceptually I think it would better if the valves were installed using a torque wrench and applying the proper torque setting.
While I understand and don't doubt that you understand what you are doing(clearly indicated above), conceptually I think it would better if the valves were installed using a torque wrench and applying the proper torque setting.
The Chairman
Chairman of the Board
I'm not an engineer, nor do I play one on TV.
I was an automotive technician for 30 years so I learned a LOT about sealing just from that. However, it was 4 years working in the Chemistry Machine shop and labs at the University of Florida that gave me a wonderful education on o-rings. My favorite times were working in the cryogenic areas where we had to deal with extreme colds and very high vaccums on the order of 10 -12 torr (sorry, no superscript available) on a daily basis. Patience and proper o-ring sealing ettiquette are essential to any success.
On a Scuba tank, the neck has been flycut to accept an o-ring, and the valve flange is used to "capture" and compress the o-ring. Once the flange makes solid contact with the the neck the torque of the valve becomes moot. The sealing of the o-ring will occur on the bottom of the flange and the wall of the flycut in the neck.
What is FAR more important, is having clean mating surfaces. Things link dirt and debris and even gaps from pitting or peeling paint create areas in which the o-ring can extrude and eventually fail. When you service a tank, you can usually see evidence of this extrusion taking place. It's important to gather information about these mating surfaces by examining the old o-ring so you can avoid ANY potential for o-ring failure. This is also why you should never re-use an o-ring.
I was an automotive technician for 30 years so I learned a LOT about sealing just from that. However, it was 4 years working in the Chemistry Machine shop and labs at the University of Florida that gave me a wonderful education on o-rings. My favorite times were working in the cryogenic areas where we had to deal with extreme colds and very high vaccums on the order of 10 -12 torr (sorry, no superscript available) on a daily basis. Patience and proper o-ring sealing ettiquette are essential to any success.
On a Scuba tank, the neck has been flycut to accept an o-ring, and the valve flange is used to "capture" and compress the o-ring. Once the flange makes solid contact with the the neck the torque of the valve becomes moot. The sealing of the o-ring will occur on the bottom of the flange and the wall of the flycut in the neck.
What is FAR more important, is having clean mating surfaces. Things link dirt and debris and even gaps from pitting or peeling paint create areas in which the o-ring can extrude and eventually fail. When you service a tank, you can usually see evidence of this extrusion taking place. It's important to gather information about these mating surfaces by examining the old o-ring so you can avoid ANY potential for o-ring failure. This is also why you should never re-use an o-ring.
- Messages
- 628
- Reaction score
- 1
- # of dives
- I'm a Fish!
:06: Did I miss something? I thought the question was regarding using eddy testing on tanks.......................... 
android
Contributor
medical1::06: Did I miss something? I thought the question was regarding using eddy testing on tanks..........................
I was suspicious of the cause of the cracked neck threads. I have personally observed the use a a hammer (not a mallet) and a large wrench to *tighten* a tank valve into a tank.
I asked a long time scuba professional and former shop owner about this practice and she said it is standard procedure. (She lives in S. Florida.)
I'm a former Navy jet mech, and this really bothers me. Anything being tighted should be torqed to a specific value, NOT hammered by an ape. This is exactly the type of abuse that WILL lead to cracked neck threads on 6061 AL which is a strong alloy, but somewhat on the brittle side as far as AL alloys go.
A 7/8-14 UNF bolt should be torqued to only 85ft/lbs, so I was curious about the torque on a valve and how it is supposed to be done. The hammer method is sure to exceed to 50-75lbs mentioned by Larry and Ontario Diver and it is delivered with spikes of force.
As a point of reference, a lot of lug nuts take a torque in the 80ft/lbs range and you don't beat on them with a hammer.
You may want to inquire the next time you get a VIP about how your valve is removed and replaced.
The Chairman
Chairman of the Board
I think the issue would be UNDER torquing the valve and not OVER torging the valve.
Most lug nuts are a 1/2 to 9/16 in diameter. Most garages use an IMPACT gun to put them on and take them off. The wheel of a car is very stationary when they tighten or loosen them.
Whalloping a crescent wrench attached to the flats of a valve on a free standing tank would probably produce far LESS than 80ftlbs. I'm OK with far less. The valve tension does not seal, the o-ring does.
I would also suggest that there is far more damage done by simply letting the tank topple over with a regulator on. This is far more common than we are led to believe.
Most lug nuts are a 1/2 to 9/16 in diameter. Most garages use an IMPACT gun to put them on and take them off. The wheel of a car is very stationary when they tighten or loosen them.
Whalloping a crescent wrench attached to the flats of a valve on a free standing tank would probably produce far LESS than 80ftlbs. I'm OK with far less. The valve tension does not seal, the o-ring does.
I would also suggest that there is far more damage done by simply letting the tank topple over with a regulator on. This is far more common than we are led to believe.
OP
silverbackmrb
Registered
What is the cost of VIP+ in your area? Guess I am getting old but $16.00 seems a little high. I see need for annual inspections but after reading up on the DOT failure reports and PSI (I think it was PSI) they say it is not needed annually on tanks other than the suspect alloy. Stress cracks are part of the five year recertification process. They also stated these were easily detected by a training technician.
I get $10 plus the air full, so $14 total.
- Messages
- 628
- Reaction score
- 1
- # of dives
- I'm a Fish!
silverbackmrb:
Have you ever seen some of the extreme pitting on aluminum tanks or the rust that can develop inside steel tanks in a short period of time. Scuba tanks get some rough treatment in a year. Visual are NEEDED annually on all tanks - not just the 6061 alloy.
No one is saying visuals are not needed.. they are saying that eddy current testing, aka Vis+, is not.
Similar threads
