[GuyBFF]

Almost all decent pumps are actually rated at 1 foot head (this is true for the Little Giant, Danner Mag-Drive, Eheim Hobby Pumps, MaxiJets). Just go to one of the web sites to verify this.

Your correct in the fact that the values at each head height display how the pump will handle resistance by friction due to a restriction, but the actual heigh of a closed loop system doesn't matter.

Make a loop 10' in diameter. Run it vertically (with 10' head hight according to your statement), then lay it flat on the ground, run it again (with 0' head hight). You will see there is no difference in flow.

Pump water from one open container to another 10' horizontal, then repeat straight up, chances are the pump won't be able to pump a thing 10' up. This is "Head Hight". In a closed loop resistance to flow (friction) is all that matters.

Also, you cannot give each bend a value in equivalance to feet. They do have a huge influence, the same as any restriction in the loop, but not due to the fact they bend, due to the inside diamater reduction. Water smashes into this abrupt reduction, the fater it's going, the more effect. However if everything was of the same inside diameter (tubing and fittings, like aerospace equipment) then the flow would be much better even with smaller tubing diameter and more bends.

Resistance declines by the speed of the fluid. If your statement where true, a Danner Mag-Drive 500 could only pump threw 10-90 degree elbows. Actually try this and you will see the more elbows you add the less the effect is in a "circulating" system.