The Physics Behind Windshield Repair Injectors

Question:

If we start with the screw piston out of the bridge, how is it that we can really get a vacuum? Wouldn’t we just be relieving pressure? I do see some kits start with the injector off the glass. I’ve just never reconciled the physics behind Windshield Repair Injectors, and it is a lingering question in my mind.

Answer:

You should start by placing the plunger in the up position and then thread the plunger into the barrel (on the bridge). Once you thread the injector in, all you have to do is pull up and turn to the right to move between pressure and vacuum cycles. The spring type injector has a spring-loaded mechanism for superior pressure control, and the injector does all the work for you.