Back pressure for valves?

Is it true that when the valves don't have enough back pressure that is what causes the bags to lose air? Because when I hit the rear of my truck up and down about 4 times consecutively I noticed my front wasabout 10 psi less than it was before I hit the rear. I don't think I have any leaks. So is this common. By the way I'm only on air so would this not happen if I had a nitrogen bottle because there would always be backpressure?

Thanks sorry if this is confusing