You want to make sure you have the piston at the top on compression stroke. Reason ? If the air seal breaks loose, the valve will drop.
You got that right!!!

Don't ask how I know, it still haunts me, even 35 years later!!

Compressing the spring, pull the retainers and the line from the compressor ruptures.

Thonk ,,, valve disappears into the abyss.

Valuable lesson for a 16 year old...