[Will N]

I never really understood how the plunger works on these things! The rubber plunger is free to slide on the shaft, so how does it exert any pressure on the grease to force it toward the tip of the gun when you press the handle inward? What's the purpose of the washer on the shaft? Seems like it is to limit the movement of the plunger on the shaft, but it would only come into play while pulling the handle back out of the gun. In my mind, the washer should be on the other side of the plunger. I'm so confused.