water heater drain mod

It is a relief valve not a vacuum breaker. The valve is designed to hold a set temperature or pressure. The spring handles the pressure part. It is designed to hold the seat down until the pressure overcomes the design of the spring, then the seat lifts momentarily so the pressure is relieved then it reseats. When you operate the lever on the valve to use it as a vacuum breaker you are over compressing the spring and holding overcompressed until the tank completely drains, unless you leave the lever set and forget to flip it back. Continued cycles of over compressing the spring nd holding it compressed will cause the spring to get weaker and not allow the valve seat properly. So, operating the lever on the valve unnecessarily can cause the spring to weaken and the valve to fail.