I'm trying to make a bellows out of a trash bag, and a pipe. But when i push down on the trash bag air goes everywhere else in the bag instead of through the pipe, and if i do manage to get the air out through the pipe its a weak amount of air, then the bag wont refill with air. Also if this helps with finding out the problem all i did was tape the opening of the trash bag onto one end of the pipe. So if anyone would let me know what im doing wrong, help would be appreciated.

the bag has to have some kind of frame . this directs the air out of opening and not just around inside of bag.
it must have a flapper or something to let air in when you pull bag up and close to hold air in when you push
down. youtube is very helpful on some of these things

Thanks for the help.

Tape two sticks into the opening of the bag, make finger holes and a thumb hole (more like straps) Open your hand while lifting, close your hand while pushing. This is the air valve.

It worked OK for me, not great. I think the shape of a trash bag might not be best. I used a kitchen trash bag for my experiment and only tried once without fire. I felt it was too wide to allow the air to be pushed out well, it always had large air bubbles. A tallish, narrow, cylinder-like bag might work better.

I am sure there are other ways to set this up.

Phil

Thanks

A dry bag (sold at REI and the like) might be the ticket. These bags are waterproof and their tops do what the two sticks would do. They are also usually cylindrical.

FWIW,
Rob