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Scott, Sean, Michael, Captn: Think hard. If the plug has a HOLE in it, how is it going to keep all the gas inside the tank if the knob gets bumped in transit? That is the PURPOSE of the plugs. Keeping the valve opening free of damage is an added bonus (sort of like the prize in a box of Cracker Jacks). Get it? When traveling I often have somewhere in the neighborhood of 30 cylinders (all with DIN valves) in the back of my van (yes it often takes 15 cylinders to do 3 dives but I wouldn't expect you to understand this). Sometimes things get knocked around a bit regardless of how carefully I pack. Now for the hard part. Pay attention please. The 316 stainless these plugs are made of have a tensile strength of 95,000 psi. The shear strength is easily in excess of 50,000 psi. So let's talk about the tank valves (which are made of brass). Typical naval brass has a shear strength of somewhere in the neighborhood of 44,000 psi. The surface area of the plugs (which are holding in the tank pressure) is approximately .622 square inches which means that a tank filled to a pressure of 3,600 psi (heaven forbid) would be applying an outward force on the plug of around 2,239 pounds. EVEN IF YOU ONLY FULLY ENGAGED ONE THREAD of the plug into the valve opening, the contact surface area of the SINGLE THREAD would be somewhere around .1847 square inches. Even if the force of the compressed gas were applied perpendicularly (which it's not), the material would theoretically withstand over 8,125 pounds of force. This amounts to a safety factor of (8,125/2,239 =) 3.63 times the actual force applied (WITH ONLY ONE THREAD ENGAGED!). With all 8 threads engaged you're looking at a safety factor of 29 TIMES! Now keep in mind that the seal is created by an o-ring and once the plug is backed out about one and a half turns, the gas which is captured escapes past the seal and then past the threads. Even when used in 200 BAR valves, there remains plenty of threading to withstand the force pushing against the plug while venting it. Now for those of you who may argue that the plug won't unscrew with the pressure trapped inside, testing reveals that it takes no more than 15 ft/lbs of torque to remove the plug from a 300 BAR DIN valve (a dirty one at that) when it has been pressurized to 3,600 psi. Try it if you don't believe me. Finally, Captn. Did you miss something along the way? In summary, one set of 104s filled with a 50% helium mix costs anywhere from $35.00 to over $100.00. Two of these plugs cost about $36.00. You figure it out. Chuck -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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