Bill Higdon wrote:
...
That is a example of a valve less pulse jet.
....

Or rather a pulse jet with an aerodynamic valve instead
of a mechanical one. A such pulse jet was also manufactured
in France under the name "Escopette" and tried on glider(s).
Probably some of these flights were on the field were I
fly since in the bar there is a picture of a vintage glider
on which you can read "Emouchet Escopette", although the
engine(s) is not visible. Emouchet is the name of this type of
glider.

The principle of the aerodynamic valve is based (as I understood
it) on the different flow of air/gases during intake and exhaust.
During intake the air comes from almost all directions into the intake hole.
During exhaust it forms a jet which is caught by the U shaped
tube and redirected by it in the proper direction, i.e. backwards.
There is some space between the U tube and the intake to allow
the incoming air to come from the outside of the U tube. The
formation of the jet is the thing that allows this to work during
exhaust despite this space.