Denole

l have restored a few American harmoniums and a French Alexandra Pear in my time and l am enjoying working on this English one. But it does not seem to pump air into the upper chamber. l have patched up all the bellows but sound only comes through momentarily from either one pedal, or both pedals pressed down together. There is nothing at all from the usual left and right pumping. Could there be such a thing as a non-return valve issue? Many thanks.