Hi waltzer,
I agree with other posts, the bags will eventually refill with air - the problem is the seal. However if you just want to use them to compact stuff for moving then you have two options:
1. Improve the seal and the valve with strong adhesive tape eg. the wide brown shiny type.
2. To save yourself some money, buy some extra stong rubbish bags. Pack the stuff, gather the neck of the back and put your vaccum cleaner into the opening. You will have to be careful to keep the vaccum away from the sides of the bags. Then wind lots of tape around it to keep it compacted. Or, you could put it into a box and tape that.
I managed to get a duvet, 2 pillows and two sheets into a box small enough to be allowed on board an aeroplane as handbaggage.