So i've been seeing some QEV's that are just squares with the 3 input sections for the barrel, chamber, and blow gun. I was just wondering what kind of QEV's are these? The pressure they can go? Price? and where I can get one?

Thanks for the answers, i'm sure this is a stupid question.

This is for an Australian supplier:
http://www.bellpro.net/xcart_program/home.php?cat=268

They are a piston type. I use mine regularly to 300 psi and fairly often to 400, and have not had any issues. You may want to inquire about availability of spare pistons if you are using high pressures.