Closed loop - who's right?

[oldyellingtang]

I have this link ( on google at rec.aquaria.marine.reefs ) to a discussion on a closed loop & was wondering who is right. There is a question about head pressure. Is there head on a closed loop or just friction loss?
closed loop link
(Scroll up to the top of the thread)

 

[dlc]

The pump has to produce a head (pressure) for the fluid to overcome the head losses of the system and for flow to occur.
Generally, for open systems, the head losses of a system are due to friction losses and the height the fluid must be raised above the discharge nozzle of the pump. If the pump is above the source then a suction head is subtracted. If the source is above pump suction then the elevation head is added to the discharge pressure of the pump.
In a closed loop system the elevation head should be equal to suction head (Because what goes up must come down)
Therefore, the losses in the system are due to friction losses.

 

[fat_tony]

I Concur.

 

[bang guy]

I agree except you need to add acceleration losses. Friction + acceleration.
You can normally count each 90 degree turn as about 1 foot of head (acceleration loss). Larger diameter tubing will have less friction loss.