This device is designed to keep potentially polluted water from back flowing into a clean water source. A backflow preventer is a requirement by our city when city water is used to fill a private storage tank from the bottom up. If the water pressure at the city site is interrupted, the storage tank could drain back into the city pipes without the valve.\r\nIn testing the pressure loss due to overcoming the stop valves, I measured about 4 PSI loss. At high water volume, the pressure loss was measured to be around 7 PSI. I had about 76 PSI in the reverse direction and there was no backflow detected. The design specification is 175 PSI max. I assume this is the maximum pressure in the back flow direction. \r\nThe design temperature is such that device should not be subjected to more than 140 degrees. This restriction could be met if used with a Water Heater that is set very high. I am assuming the high temperature would possibly damage the edge around the seal by melting or softening the seal material. This softening might permanently damage the seal. The rubber gasket seal from valve to pipe might also be temperature sensitive. Nothing was said in the documentation about the reason for the 140 degree limit.\r\nMy city requires 2 or more back-flow check valves when connecting city water to well water or city water to an open water tank. There is a possible problem in that this double check valve cannot be tested with the standard city test. The test requires pressure testing between the two check valves. I would need two of these valves to perform the test. Two of these valves are the equivalent of 4 check valves, so it should qualify for the testing as you can put the pressure meter between the valves. \r\nWith a reducer coupling, I was able to convert the valve to 3/4inch pipe at both ends.\r\nSeems to be well built and sturdy. I liked it.