Hello Simon,  There are many shortcomings that yield the same results
you have.  Obviously, from looking at your YouTube video, the primary
problem is a shortage of air in the reservoir section.

Finding the air leak or leaks is a very challenging task.  Almost every
glue joint and valve are suspect and at some time I have had every one
of them in my work.  If you contact me directly, perhaps I can give you
some hints for finding a leak.

Moe Goldy
mgoldy@earthlink.net.geentroep [delete ".geentroep" to reply]