Use something like a ping pong ball. With a little PVC plumbing you should be
able to make a one way valve. A kitchen sink stopper might also work,
depending on the size of the hole.

Mike
**********
I've a vacuum pump which is to small for the larger parts but works fine for
most of the smaller panels used in my design.
For larger panels, i will support the vacuum pump with a hoover at start time
which works also very good.
My problem now:
When i remove the hoover, all the air comes inside (of course) very fast until
i've closed the adatptor.
Has anyone of you a good solution for this or are any special parts on the
market for that purpose ?
Hope anyone can help me with a good idea...

Best regards

Roger