Aeromech

I can't see it. Have you taken one apart? I have. It's a simple rubber flap covering a hole. Air can flow one way but the flap blocks it the other direction. I blew the crap out and now they work great.

VTX1800N1

High pressure causes the flaps to flutter and weakens them. That damage shortens their life. For the minimal cost of new ones, the peace of mind is worth it.

In addition, if you aren't very careful to absolutely disconnect every other part of the system, the IWEs and especially the vacuum reservoir can be damaged. Several have found out the hard way with the reservoir when the put pressure to the system and hear it pop.

Aeromech

I had replaced both check valves with the O'Reilly ones last week. The other day I went back and checked them and found that one of the brand new ones was flowing both ways. This was before I blew out the system. So since I had an original that was now working because I BLEW IT OUT I reinstalled it. Just so you understand, I did disconnect all the lines and the air box when I did the 50 pis blow job. That was the only way to clear the obstruction short of replacing the line going to the drivers side.

Yesterday I took apart my failed IWE and found that originally it had been made with a thin metal flat ring around the periphery. This flat ring had rusted and broken into three pieces which collected in one area stacked on top of each other and prevented the gear from moving evenly in and out.