I have not seen a geyser effect like the one they describe below!
The air (under about 9 atmospheres) of pressure expands just like steam
in a real geyser if it reaches the exit pipe. This lightens the column
in the exit pipe allowing more air to escape and the geyser effect happens
as the huge amount of compressed air in the bottom chamber blows out to
Quite an interesting bit of old technology! Perhaps you know of tromp uses in your area? If you do, please let me know.
Swiss and french alpine tunnels were constructed using tromp power. Tell me some of the details!
Airlift and tromp reference page