I'm confused about why external pumps and filters have maximum 'head heights' - the distance below the surface of the tank that you can put them. (My tank is mounted in a wall, pretty high up, and I need a big height gap between the surface of the tank and the filter/pumps).
Why aren't the only relevant factors the pressure differential between the intake and the output of a pump (e.g. if one is much higher), and the length and curvature of the pipe (for flow resistance) regardless of whether it goes up or down? Any filter or pump is a closed circuit (in my understanding) and so should have equal pressure throughout once it's filled with water - so it shouldn't make any difference at all whether the pump is below or at the same level as the surface of the tank.
Basically, for each ml of water you pump up, another ml is coming down, equalising the pressure on the pump... no?
Maybe the issue is to do with initial priming...? Can anyone who understands physics properly explain? Or is it something manufacturers just write on pumps for no reason?
Why aren't the only relevant factors the pressure differential between the intake and the output of a pump (e.g. if one is much higher), and the length and curvature of the pipe (for flow resistance) regardless of whether it goes up or down? Any filter or pump is a closed circuit (in my understanding) and so should have equal pressure throughout once it's filled with water - so it shouldn't make any difference at all whether the pump is below or at the same level as the surface of the tank.
Basically, for each ml of water you pump up, another ml is coming down, equalising the pressure on the pump... no?
Maybe the issue is to do with initial priming...? Can anyone who understands physics properly explain? Or is it something manufacturers just write on pumps for no reason?