Can somebody tell me what something like this would be called? I'm going to run some copper wire from the bottom of the cattle trough. Run it over a fire with a few coils, then back into the cattle trough near the top of the water. As the cold water is heated in the copper, it will expand pushing the warm water into the trough. That will leave a vacuum in the pipe and so cold water will be sucked in through the valve. Then it starts over again. I just need to know what valve to go buy.