Vacuum Bagging Pump size needed?

I am currently using a recycled automobile aircon compressor hooked backwards driven by a small electric motor via v belt.

 

My first vac. run was using my v6 car engine, pulled brake booster line and adapted my vacuum line. 18" of vacuum.

 

If the pump fails, won't the laminate decompress and suck air into the laminate?

 

If it decompressed after he sucked out the excess, he would just have to add more resin, I would rather have a cheap backup pump on hand.

 

The vac bagged part should be able to hold the part minimum of 2 hours without vac. If the vac fails before the resin has set, most likely you will get a springback, pre release, or worse, resin starvation on vertical surface.