Stand by your statements if you like but that doesn't make them true or correct. If yoke regulators were inherently unsafe to use at 3442, Worthington and PST wouldn't be supplying their E-series tanks with 232 bar convertible valves.
Using 232 bar yoke on HP 130 steel tank
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Stand by your statements if you like but that doesn't make them true or correct. If yoke regulators were inherently unsafe to use at 3442, Worthington and PST wouldn't be supplying their E-series tanks with 232 bar convertible valves.
Jimmer
Contributor
The load is only supported by 2 or 3 threads, end of story. You're right about more surface area, which is why high strenth bolts like aerospace grade are often fine pitch, because the minor diameter of a fine pitch is greater than the minor diameter of coarse pitch, therefore having more cross sectional area and more strength. If you look at a lot of cylinder head bolts or studs, the threaded section is often larger in diameter than the shank of the bolt. This is because they spec the shank of the bolt to be the proper diameter for the load, and then use a thread with a minor diameter equal to or greater than the diameter of the shank, so there is no spot on the bolt that will be under greater stress than the shank. The surface area of the thread engagement really has little to do with the strength of the threaded assembly. Some race car fabricators I know swear by fine pitch simply because they can torque them more accurately since a given degree of rotation means less linear travel of the bolt or nut. Also not all engines use fine pitch, I know this from experience rebuilding small block chevy engines, and a few high revving japanese motorcycle engines as well. In fact when threading into a casting, coarse is often preferred because the minor diameter is smaller and therefore the threads engage deeper into the casting, and will be less likely to pull out. Most race car engine builders I have met prefer to use cylinder head studs that are coarse threading into the block and fine at the head for torquing them down.
The standard DIN O-ring is a number 112, which coincidentally happens to be the exact same one as in many of the old yoke Scuba valves.
I like the O-ring design of new Sherwood style yoke valve better (it uses number 014).
Here are some good references for SCUBA O-ring sizes:
Oxygen-Compatible O-Rings and Lubricant for SCUBA Applications
How to Buy O-Rings For Scuba
Here is a good source for O-rings and it has a good table with the actual sizes for the different O-ring numbers:
How to Buy O-Rings For Scuba
This is also a great resource, the Parker O-ring Handbook. Parker basically wrote the manual on O-rings and similar sealing technologies..
Parker O-ring Division -- The World Leader in Seal Technology
What are you basing this opinion on? Experience? Or just something pulled out of your rear-end?
The flaw in your argument here, is you seem to forget, the weak point in a yoke configuration under high pressure, is the o-ring. The o-ring will blow long before the metal of the yoke would deform.
Captain CaveMan
Contributor
I based my post on my Experience with working with steel. Engineers are not correct all the time. After working for Semi-truck dealerships I see tons of mistakes they make. But they stand by there ideas and look down to us techs because they think were just grease monkeys. There are many times that we had Engineers come to the dealership to look at problem trucks to find out that there design sucks and ask us what we think what we think will work. ( thats the smart engineer. IMO)
"Ok if the o-ring were to fail before the yoke" . Do you think that the yoke could have be stretched ( im talking .0002") causing the o-ring to not seal.
On semi's for the rear axle u-bolts we use fine threads bolts and nuts. After torqing them down some times up to 1000 f/pounds (style of Suspension) we are prestretching the a bolt made for this. But after time could be days or months the bolts become loose. This is why we never reuse u-bolts. All im saying is that with my knowledge the 300bar din style connector is stronger.
"Ok if the o-ring were to fail before the yoke" . Do you think that the yoke could have be stretched ( im talking .0002") causing the o-ring to not seal.
On semi's for the rear axle u-bolts we use fine threads bolts and nuts. After torqing them down some times up to 1000 f/pounds (style of Suspension) we are prestretching the a bolt made for this. But after time could be days or months the bolts become loose. This is why we never reuse u-bolts. All im saying is that with my knowledge the 300bar din style connector is stronger.
Jimmer
Contributor
I'll be the first to admit that what works on paper doesn't automatically work in the real world, and asking the guys that deal with the items day to day is a good idea. But you can't change physics. 7 threads doesn't hold a load better than 5. Also I know exactly why you never reuse bolts and when I was engine building we mic'd the main bearing bolts to check torque and stretch. I know all about that. Working on race cars teaches you a few things, and one thing I've learned is that transport trucks are built way overkill, and for a damn good reason too.
Guility! That's me.
When we put 1,000 foot-pounds on a fastener, that is some real heavy-duty clamping force. The forces of the truck going down the road are going to try to stretch that bolt, perhaps a hundred times a mile. We don't want the bolt strteching long and short like a rubber band, as it will work harden and.... snap! When tightened correctly, it has clamping force that will be greater than the forces trying to stretch it, and it will stay stretched, not going long and short. That's how it lasts many thousands of miles.
With correct installation, the bolt stretches only once, at installation.
Here's where my dive pals get confused. Compared to industrial gas and mechanical equipment, dive gear isn't "used" that much. That regulator yoke may stretch a tiny wee bit, but how many times? How much force? If we used it once a day for ten years, that's 3,650 times. Not many of us have over 3,000 dives, and probably very few regs do, either.
To see how long the yoke would last would require an experiment. I can only estimate, that the yoke will probably outlive the diver. What do you divers think?
Stu
The inside diameter of the pressure interface in both a yoke and a DIN connection is about 0.5 inches, therefore the pressure area is about 0.196 inches square.
With a pressure of 3500 psi the pressure thrust is 687 pounds.
With a pressure of 5000 psi the pressure thrust is 982 pounds.
The minimum cross section area that I could measure on a 232 bar yoke is 0.125 inch square per side (two sides of 0.25in x 0.5 in). Therefore the maximum tensile stress on the yoke is only 3,927 psi (at 5000 psi).
Determining a worst case bending stress requires some very conservative assumptions since the geometry is intentionally design to minimize any bending (this is a good candidate for a Finite Element Analysis model, but I am not spending any more time in this issue). With some very conservative assumptions I come up with the worst case bending stress to be about 6,300 psi.
This stresses are well below the yield stress of annealed Naval Brass (25,000 psi), but most likely it should be compared to half-hard Naval Brass (yield strength = 53,000 psi). With this kind of loads alone it would never reach any fatigue failure of any kind.
The maximum elastic deflection I can calculate is about 0.0001 inches for the section in bending. The total cumulative deflection could easily be a few times that number.
And yes, all materials will flex under any load. In the elastic region, the deflection is proportional to the load, if the load is insignificant the deflection is insignificant. Any flexing that does not reach yield strength is defined as elastic flexing and the deflection will return when the load is removed.
The bottom line is that the modern heavy (232 bar) yoke attachments by design have a large safety factor even if used at 5000 psi (no surprises there, see note), and if they are not damaged, deformed in any way, and properly secure, they can handle any pressure encountered in Scuba diving.
DIN attachments do have the advantage of not having the yoke screw knob sticking out the back.
The 5 or 7 threads on any DIN fitting are barely loaded under any Scuba pressure (unless there is any sand grains trapped in the threads, but that is a different story).
BTW, Jimmer, if I recall correctly, the classical thread analysis that shows that the full strength of a screw can be carried by only 3 threads mostly applies to male and female threads using similar material Young’s modulus. This coincidentally does apply in this situation.
Unquestionably I have made mistakes. That is not because I am an engineer, but because I am human. One mistake that I have always avoided whenever possible is that of not listening and learning and learning from everyone around me. That will specially include all the technicians, mechanics, welders, fabricators, and other engineers both degreed and non-degreed engineers that I have had the luck to work with. And yes a few of the sharpest engineers I have had the pleasure to work with did not have a formal engineering education and many of the sharpest people I have ever met where technicians, etc.
In my engineering education one important point we were taught is that we only had the tools to keep learning…the learning never ends (this obviously applies to Scuba diving and live in general). Any day that I learn something new, it is a good day. Keeping an open mind is a good thing.
Added:
Note: This is a consumer item, if you don’t think a simple consumer item like this doesn’t have a huge safety factor, you are forgetting…this is America; if someone gets hurt, some will get sued. It would be very easy to calculate the structural safety factor on a yoke or DIN connection. I basically already did it.
With a pressure of 3500 psi the pressure thrust is 687 pounds.
With a pressure of 5000 psi the pressure thrust is 982 pounds.
The minimum cross section area that I could measure on a 232 bar yoke is 0.125 inch square per side (two sides of 0.25in x 0.5 in). Therefore the maximum tensile stress on the yoke is only 3,927 psi (at 5000 psi).
Determining a worst case bending stress requires some very conservative assumptions since the geometry is intentionally design to minimize any bending (this is a good candidate for a Finite Element Analysis model, but I am not spending any more time in this issue). With some very conservative assumptions I come up with the worst case bending stress to be about 6,300 psi.
This stresses are well below the yield stress of annealed Naval Brass (25,000 psi), but most likely it should be compared to half-hard Naval Brass (yield strength = 53,000 psi). With this kind of loads alone it would never reach any fatigue failure of any kind.
The maximum elastic deflection I can calculate is about 0.0001 inches for the section in bending. The total cumulative deflection could easily be a few times that number.
And yes, all materials will flex under any load. In the elastic region, the deflection is proportional to the load, if the load is insignificant the deflection is insignificant. Any flexing that does not reach yield strength is defined as elastic flexing and the deflection will return when the load is removed.
The bottom line is that the modern heavy (232 bar) yoke attachments by design have a large safety factor even if used at 5000 psi (no surprises there, see note), and if they are not damaged, deformed in any way, and properly secure, they can handle any pressure encountered in Scuba diving.
DIN attachments do have the advantage of not having the yoke screw knob sticking out the back.
The 5 or 7 threads on any DIN fitting are barely loaded under any Scuba pressure (unless there is any sand grains trapped in the threads, but that is a different story).
BTW, Jimmer, if I recall correctly, the classical thread analysis that shows that the full strength of a screw can be carried by only 3 threads mostly applies to male and female threads using similar material Young’s modulus. This coincidentally does apply in this situation.
Unquestionably I have made mistakes. That is not because I am an engineer, but because I am human. One mistake that I have always avoided whenever possible is that of not listening and learning and learning from everyone around me. That will specially include all the technicians, mechanics, welders, fabricators, and other engineers both degreed and non-degreed engineers that I have had the luck to work with. And yes a few of the sharpest engineers I have had the pleasure to work with did not have a formal engineering education and many of the sharpest people I have ever met where technicians, etc.
In my engineering education one important point we were taught is that we only had the tools to keep learning…the learning never ends (this obviously applies to Scuba diving and live in general). Any day that I learn something new, it is a good day. Keeping an open mind is a good thing.
Added:
Note: This is a consumer item, if you don’t think a simple consumer item like this doesn’t have a huge safety factor, you are forgetting…this is America; if someone gets hurt, some will get sued. It would be very easy to calculate the structural safety factor on a yoke or DIN connection. I basically already did it.
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