Most of the time they are for plugging culverts that lead away from a drainage area around a chemical plant or a refinery. Workers will plug the culvert and pump chemicals or oil out of this basin to keep it from going into a water way. It is important to note that most of the time the basin drains into a river or wetland, and that most of the time there are no leaks. These are strictly for emergencies.
Sometimes they are designed to test spillways. Two similar to this were used to test the seal around the spillway at the Animas Laplata Project in SW Colorado. Special parts are put on them to help hold them in place, and special valves, hoses and valve placements are used to make them easier to use.
We even made them to plug vent holes and truck access in the Ekati Diamond Mine in Canada. Ekati produces 6% of the world’s Diamonds. A couple of our plugs were 14 feet in diameter, and one was a 23.5 ft arch with a screen instead of being all the way inflatable. It tied to the framework of the truck tunnel.
Last year we produced plugs that sat alongside of large cement and Iron Gates at a water facility in Detroit. This one required that water be used so the tubes did not float out.
This year it was a project to actually plug a square 12 X 5 ft. culvert while there was water in the culvert. Once again we decided that water would be used to keep the unit from floating out of the culvert. Buoyancy effect can be a very large force. This is the one I wanted to concentrate on because it has some different features that we have not done before, and because of its size.
Faced with a decision to purchase our plugs or a metal gate that sealed off the water, our customer opted to try this idea. While we were talking we came to the realization that the buoyant force would work against us, so we devised a way to support the weight of the water by using pipe and Channels and tie them up to carry some of the water weight. This is in a tidal pool, and the weight of the water in the plug can make it act like a big water balloon, so the channel and pipe idea was a good one.
3 inch bulk head fittings were added to the chamber to help get water in and out.
At the end of the design phase we were asked to put in an area where a 12 inch and a 6 inch pipe could fit at the bottom of the culvert. We used closed cell ethafoam to help seal the spot between the fabric and the pipes.
We decided to use 3 psi Pressure relief valves, but this did not work out well in the testing process. We believe that we had a geometry problem. There were 2 different hoops, and pressure overcame the small hoop and turned the fabric around the 12 inch pipe relief causing it to pop out rapidly, and it ripped. We fixed that, and went to a 1 psi pressure relief valve. We had an explosion. This is when we learned a lot about geometry vs air pressure.
One of the ideas was to have air pressure on top of the water that would help wedge the plug into its cavity. Math is important here. 12 ft. x 4 ft. with 1 psi (assuming some distance at the top for air pressure) puts 6912 lbs of force on the inside surface of that plug. Buoyant force would be 14,980 lbs. This is equal to the weight of the water inside the container, and is the displacement force if air were being used to inflate instead of water. In other words it would take something that weighs 14980 lbs to sink this thing full of air all the way into the water. This is also called displacement, because the weight of the water being displaced is equal to the weight on top of the inflatable forcing it down.
What about the Explosion: It was not a pretty thing. This 100 lb. unit flew up in the air and spun at least 180 if not 540 degrees. The energy released at 3 psi from such a massive inflatable destroyed 2 picture windows in our shop. I personally flew a number of feet and fortunately did not hit my head.
We are going to be real careful in the future testing for pressure. We now know that hydrostatic pressure testing is a superior way to test for pressure because water cannot be compressed, and does not hole kenotic energy the same way that air does. However it would not have been practical to test this hydrostatically. It is just too large for our shop.
The plugs are still doing their work, and we will have an update on this project’s success or failure in the very near future.
Here are some pictures of the installation:
threading the pipe that holds some of the water weight via the fabric channel
adding water and toping it off with air pressure
6 inch and 12 inch pipes in place under the plug
Here is a pressure bag that we made for BYU. The university is trying to develope a light weight lift bag that can lift up 25,000 lbs, but is not too heavy. this one was 14 lbs with the web. We had strap failure because the thread in the sewing was not strong enough. It is interesting to note that in the video many of the straps were broken before the inflatable broke. This is a hydro static test.
See the vieeo of destruction on you tube.
I calculated without the straps the nflatable would break at 10 psi. We have a new one on the way that they will test without the straps. They were trying to get to 50 psi. It is possible that with Vectran web, and the proper stitching, it will make it to that mark before breaking. They only need 25 psi to make it lift 25,000 lbs, but they needed a 200 % safety margin to pass the test. This whole thing exploded at 34 psi. We will keep you informed on how it worked.
Thanks for reading this.
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