Yes but it's the positive pressure that's important, not the high flow rate. You may need a high flow rate to maintain whatever pressure you're aiming for but the thing that's keeping out any contaminants is the fact that every tiny leak is only going to have air going from the inside to the outside other than the filter itself. If you've got a big room with only one tightly sealed door, you don't need a lot of flow to keep out any contaminants.
