I rebuilt a NIRA FFM the other day that had an exhaust valve that absolutely would not allow air to pass. I poked it open with a dull probe and it worked like a champ the rest of the time. It did not seem sticky when I poked it open but it would not pass gas when I exhaled hard into the mask. Damn near blew the mask off my head!!
I should hope not, it would be real bad if it did when you had it on......:coolingoff:
Sorry, just too good to pass up.