advice on a champion spark cleaner and tester

[tango07]

I have a spark plug tester that used to work but not any mpre.it is a champion brand, with a canvas bag wrapped around it. can any one tell me if the bag has to be inflated ? when the air is applied.or is the bag only there to hold the carburundum powder. i think it was made around 1945 or1950.
none of the pipes are blocked. thank you. John.