Just recently started using my bushkill style vacuum, the damper is a must. I like to adjust mine to where it will just barely pull on my tshirt. I have used mine 4 times now and had very, very few dead bees. don't know what style you are using, but I highly suggest the bushkill model. The bees seem to do much better with frames and such to hold on to. I used a friends bucket type this weekend and am convinced the bushkill type is much better for the bees well being