Manual Leaf Blower with reverse gear
The pump costs around 20 Euro in a DIY shop, it is a simple bilge pump with two connections, one to suck in the air (sorry, I meant to say "bilge water"), one to blow it out. Capacity is 2x2 l, which means that whenever you pull or push the piston, you will move 2 l from one valve to the other. Originally designed to pump water, it apparently works fine with air as well. It comes with several end-pieces to vary the water stream or fit air matresses, balls, rubber balloons (the "normal" small ones) etc. There is also a 0.3 bar one-directional valve to prevent pressures higher than 0.3 bar, which can be removed, if necessary. This pump is available online too, I think. Look for "explorer doppelhub-kolbenpumpe".
Additionally, I bought a water exhaust pipe of 5 cm diameter, an end-piece to fit into it and a rubber plug that fits into the end-piece. This gets the diameter down to the hose of the bilge pump. No extra sealing required, you only need to stick everything together. Available at most DIY shops in Germany, cost about 6 Euro.
Possible uses for our range of activity:
Inflate inflatables of all sorts to low pressure (I don't think, it can handle bicycle tyres)
Deflate deflatables of all sorts (but apparently no self-vaccuuming)
Create an intense PVC smell in your room
Tested on:
Inflatable (dual-wall) latex sleeping bag. Very effective, but you can only inflate it to a certain extent, if you still want to get in. And while in, you need a single-action pump, assuming, that you can push to pump and lift the pump to get the piston out for the next push. The additional exhaust-water pipe was not needed here, one of the adapters fit well.
Giant climbin-balloon - see my separate threat here:
https://www.likera.com/forum/mybb/Thread...In-Balloon
Advantages:
Cheap
Almost silent
Much faster than a bicycle pump because of the huge piston
2-way action, push and pull
Disatvantages:
Manual and therefore slow
Cannot be used, when seriously restrained
Unless you are very small, you cannot operate this pump while standing upright
Possible improvements:
Make more adapters, when needed
Create a rest for the pump, where it can be operated while standing upright.