The valve is "pilot operated" meaning it requires significant pressure behind it for it to open.
I've had people expecting that they should be able to blow through it (using their mouth) and it won't pass any wind that way. That is normal. Put a 10-12 PSI air hose on it and it should open and close just fine. If not, spray it with WD-40 and exercise it a few times using higher pressure (80-100 PSI). If it still won't open with low pressure, then it probably needs replacement. With no pill, the valve flows almost 8 GPM @ 100 PSI, so it has capacity at pressure.
The stems don't come apart.
Spud