Can I make a vacuum pump with a aquarium air pump modified?

dont know,
but if you can generate 7-10 psi of vacuum it should work ok.
low flow rate may be an issue, but that just means you need to do a good job sealing the bag.
home jobs are generally made from the compressor out of an old refridgerator.
-bill

I tried it and the big aquairum pump I used would not generate enough vacuum or move the air quickly enough.

You can make one with a refrigerator compressor.

see http://www.paragoncode.com/shop/vacuum_pump/

http://members.ozemail.com.au/~flyingwing/vacbag/

I bought an automotive a/c repair vaccum pump on ebay for $75 including shipping.

check out http://www.joewoodworker.com

he has detailed instructions on how to make a very serious vacuum pump. also sels them at a fairly reasonable price.

JJ

if you have compressor check aut PIAB - They produce eduction pumps. Quite cheap, quite and small.

Dirk

Not sure I follow the link between PSI and vacuum but if you do get setup, and the refridgerator setup described well in two links detailed here is the best bang for buck, you will want to draw a minimum of 20Hg for a good vacuum result.

For the record I started out with a 'fridge pump which got tired as it lost its oil and I bought a Gast DOA compressor(60psi)/vacuum pump(28hg) on ebay for $40 which works excellently. It also doubles as the compressor for my airbrush as the fridge setup does not provide the airflow.