If your valve does not function correctly, it is most likely because debris got inside the ASCO air purge solenoid. This procedure tells you how to clean an ASCO brand air purge solenoid.
Close the primary air valve. This stops the air supply to the machine.
Remove the red cap . Push the solenoid coil assembly  down to compress the spring inside. Remove the specification plate . Remove the split spring  and valve subassembly  from the coil assembly . Disassembly the valve subassembly .
Clean the parts with compressed air. Be sure to remove all debris from inside the valve.
Apply a thin coat of high-grade silicone grease to the body gasket . Assemble the components in the opposite order they were removed.
Open the primary air valve. Make sure there are no leaks.