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Air Intake Backflow Preventer necessary?

Hello,

I live in a cold climate and our installer put an air intake backflow preventer on our hotwater power vent heater.  It is a new installation and the backflow preventer started making this huge mechanical knocking. I've isolated it (without a shadow of a doubt I know its coming from the preventer). It seems that the blower hiccups (inhales, exhales) really quick every time the heater fires and it slams this preventer open and closed. Its extremely loud and sounds like someone is bashing the pipe. 



In the picture the blue arrow is where I disconnected (to test) and the red circle is the backflow preventer.



Are they necessary? Can I just cut out that preventer and install a straight pvc pipe in its place?