Very different reason I chose pull type. ;P
To save my precious time, I will quote a post:
"The push type blow off valve stays closed under vacuum conditions by a spring that is inside it pushing against the main valve that opens and closes. The spring has a rated pressure level on it that will not allow the valve to be open until a certain pressure level is achieved. The little nipple that you see on the side of the push-type blow-off valve is attached directly to the intake manifold via vacuum hose and shows the valve vacuum pressure at idle. When the vehicle is on-boost, the nipple shows positive pressure and that pushes the diaphragm closed which allows boost to build up inside the piping. Since the positive pressure in the intake manifold equals the positive pressure in the intake pipe, the valve remains closed until the throttle body closes and vacuum is applied to the blow-off valve, allowing the pressure built up in the piping to push it's way out of the piping past the valve to the atmosphere. This rush of air exits out the vent port, and depending on the structural configuration of the vent port, it can make a very unique sound. I personally do not like this type blow-off valve, as it is prone to leakage like a ******'s ***, is slow to respond and requires rebuild from time to time. The adjustment nut on most of these valves allows the user to adjust the stiffness of the spring to their personalized settings. Much like Pandora's box, this was a bad ****ing idea. The root of 'BOV tuning' came from this adjustment nut. So now any ****head with a wrench and an allen key could 'tune' a blow-off valve. Beautiful. And I thought the Tactrix cable was a bad idea.
The other type of blow-off valve is the pull-type blow off valve. I find this valve to be vastly superior to the push-type valve for many reasons. Number one, the valve is held closed in place by the actual boost pressure in the pipe, not the line that feeds from the intake manifold. You'll never have a leaking issue with this one at higher boost levels because of a compromised diaphragm in a push-type blow-off valve. When the car is on boost, the valve stays shut all the way, 100%, as the positive boost pressure on the pull valve helps ensure that the valve is shut on boost. When the throttle body is closed, vacuum pressure is immediately applied to the pull valve and the pressurized air escapes immediately."
-Eric Smit
