Sandor

I do understand, but not all UAT's have a bag inside them, I think its only the BVM one that does, the others, certainly mine have a multi pleated paper filter attached to the fuel feed pipe solidly in the middle of the tank, admittedly the multi pleated paper will have a greater surface area than the Orbit clunk, but I still do not see where the air comes from, cavitation can only cause air bubbles inside a fluid if the air is persent in the fluid already or can enter in some manner by suction, if we take this to its logical conclusion we are saying that if the pump is cavitating it is drawing in air from either the pump seals or the fuel feed connections, if not where is the air comming from?

Going back to my days of study in fluid dynamics a pump will only cavitate if it has demands upon it that are outside its operating capability i.e. demand is too much or supply is too little, its at that point that air will enter the system from one end or the other, but only if air is able to get into the supply or demand pipework, once a pump starts to cavitate it will no longer pump effectivly, therefore if the supply is an open end air can be drawn up the supply pipe into the pump and eventually it will stall if the demand remains high enough, so I suppose I have answered my own question. its either the clunk not able to supply enough fluid to stop the pump from cavitating or the pump is of insuficient specification to supply the fuel required, interesting stuff very thought provoking my old brain needs a jolt now and again. LOL

Mike