I bought one of those Simplex Valve Testers years ago.  What a waste
of money!

It was designed to clamp on the pneumatic unit.  There was a bleed in
the tubing that was tubed back into the suction supply.  There was a
small spring-loaded bellows with a flap valve, exactly like a mini
pumping bellows, which supplied suction to the whole affair.  By count-
ing the number of seconds it took for the bellows to open, you could do
three tests: valve closed, valve open, and repetition and valve opera-
tion.

All you have to do to make one of these is to copy the opening on your
stack board out of a block of maple.  Insert a nipple to the valve
chamber hole, and a large nipple to the suction supply.  You will have
to insert a bleed from the pouch input back to the main suction with a
"T" connection, leaving one end of the tubing open to operate the
valve.

Design this so the pneumatic unit can be screwed to the board, rather
than relying on clamping.  The PPCo unit never clamped securely enough
to the unit without leaking, and that spoiled your test.

Hope this helps,
Andy Taylor