Hello again! I'm trying to replace the trigger valve assembly in a Paslode narrow crown stapler, it doesn't feel as if it is threaded in since I turn it and it does not want to gain any in height. Does it simply pop in and out?

Actually I found the reason it woud not come out. There is a roll pin that holds it in place. I am still havine the same problem though as to why I need to change it out. Air rushes out of the assembly just like the one I am replacing so it will not plunge the driver blade down. What could ths be?