Pull Trigger, loads, then releases chamber?

[Doc j]

Hi.
Came across pics of this a Classic
A. S. ENGINE.
I like idea of its simplicity.
Would like to do something similar.
With one hose going in.
Unsure how it works.
Any ideas.
Is it just sorta a spool valve concept.
P. S. Had a pic with the trigger attached but couldn't upload it.

[jackssmirkingrevenge]

Here is one working:



Looks like it is basically the same concept as a NBB airsoft gun.

A double action trigger seals the chamber and then knocks open a valve poppet.