[redleader]

Head is the height that the water can be pumped to vertically. pump with 26feet of head can pump up to the exit point of hte tubing 26 feet above the height that hte pump is at... obvioulsy it can pump more than 26 feet if the tubing is at the same height relative to the pump. it could pump much much furter.. but stil there is a point when the resistance of the water in the tube will cuase the pump to stop flowing even if the tubing is horizontal. this is just because the water would be so heavy that the pump could not start moving it.

Yes, but it has units of pressure, hence my point that you should think of it as pressure and not distance.

not that this maters but water isnt compressable. if you take water that is 10 thousand feet below sea level (not that there are any places that deep i think) and bring it to sea level it wont get any "bigger". But this doesnt apply to water cooling.

All things are compressible, water included. Water at the bottom of the ocean is actually denser then at the top because its under a lot of pressure. My point was that we can ignore this in most liquids and solids because they don't compress noticably at the pressures we deal in.

ok given that information, the pressure drop will be the same or the deltaP (p is pressure) will be the same no matter what the flow is (given it isnt like .0001gp) Well if it is earlier in the loop then the pressure drop will be the same but it will start at different points. lets say the pressure drop is at 4. just a random number 4. so the pressure is 10 before going into block 1. after block one the pressure is 6. now lets say it goes through the exact same type of block right after the first one. now the pressure is 2. voodoo based on what you said that would seem to be correct. and that has been my point the entire time.

You don't seem to get that its all relative. When you say that the pressure is X, you're saying its X higher then something else. Could be the pump inlet, could be atmosphere, could be vaccum. Lets extend your example:

Lets say a block is right after a pump that produces 5 PSI of head above atmosphere. The drop across the block is X-3, where X is the high side pressure. Thus after the block the fluid is 2 PSI higher then our reference (5-3 =2). So far so good.

Now lets move the block to be after the res. As you said, an open res is at atmospheric pressure, which is zero in our example (since I speced the pump head in psi above atm). In this case the high side of the block (X) is at 0 PSI. And the low side is still X-3 since we agree that flow cannot vary in a series loop. That means that the low side is 0-3 = -3 PSI above the atm, or more commonly it is 3 PSI below atm.

Now do you see why absolute numbers are unimportant? We can construct arbitary values at each point, and it doesn't really matter provided the drops are constant. Lets say we take the loop to the bottom of the ocean. Now X might be 10000, and X-3 = 9997 PSI. But the difference is still 3, and the flow is the same (ignore that the water is a few percent denser and thus acts a little different in the block probably shifting the pressure drop slightly.)

Is there some ambiguity still why it doesn't matter where the pump is? If so be specific what part of my explination you disagree with or do not understand.