Originally Posted by WhyFi

My new valves (Milkit) came in yesterday. I was dragging my feet on swapping them out, but your post goaded me in to it. These valves will keep pressure in the tire with the valve core removed, which is nice if your tires occasionally come unseated when completely deflated. The swap and re-seat all went smoothly, but I wasn't ready for the violence of the air pressure shoving the sealant syringe piston - POP! I guess that's why they recommend taking the tire down to 20psi or so before removing/adding sealant.