QEV Question... I have been watching some videos and is the function of a QEV entirely dependant on pressure so it functions automatically?

Also, its this suitable as a dump valve? http://www.ebay.co.uk/itm/1-4-PT-Mal...item2c7ab4335a

I am guessing if you are putting the dump valve between the buffer and main tanks you only need one as both can vent via the same port?