How do u know if you have an airlock in your system and how would you cure it ? Also if my Shutflo 100 psi pump were to run dry for a few minutes would this damage it for Eg. If water runs out and pump still running ?

i get it a lot at the moment as i empty the filter bowl and inlet pipe to stop them freezing.
the pump runs but nothing comes through.

the easiest way to cure it is connect a hose to the out of the pump and suck, it clears it instantly.
or you can try to force pressurised water through the pump from a  house tap/hose

Certainly air bubbles in the outlet is a pointer to an airlock. Also you can sometimes find the  pump will cut out intermittantly and then cut back in again with reduced pressure at the brush head.
Do you use a flow controller? If you do and it has a dead end facility you can clear the air lock by wacking the cal value up to max. This is simply a way of increasing the water pressure which pushes the air through.May take a couple of hours of pump running to clear it out properly.
Make sure to turn the cal value back down again when the air loc is cleared though. It makes things easier on the pressure switch of your pump.