If you end up with a perfect seal on the vacuum bag you will only need the pump to draw the air out of the bag and create the vacuum, you can then close off the air tube and leave the sealed bag under vacuum. If you don’t achieve a perfect seal (which is likely to begin with) you will need to run the pump whilst the resin cures, which could be as long as eight hours. You need to bear this in mind when deciding what to use as a pump, professional composite vacuum pumps usually operate in two stages, to draw air out in high volume and then to maintain a (close to) full vacuum for a long time. They can safely be run for several hours as long as the leaks in your vacuum bag are very small, the same may not be true for your hoover. If your bag loses pressure before your part is fully cured it will not be sufficiently compressed which will lead to voids inside the part, filled with either air or resin, which cause weaknesses and added weight.
An alternative to using a full bag is to use a single sheet ‘half bag’ which attaches directly to an open mould. Rather than preparing a bag as described above you can prepare your mould with double sided gum tape around the edge. You will need to add surplus bagging film, to allow the bag to drape inside the mould fully, by adding pleats, as pictured. This can take longer to finish and therefore is more suitable to a resin infusion
technique rather than wet lay up, where you are under a pressure of time as the resin cures.