<a href=showthread.php?s=&postid=10371807#post10371807 target=_blank>Originally posted</a> by der_wille_zur_macht
There are lots of things that can cause "head loss."
The most obvious is just the actual head the pump is working against, i.e. the vertical distance it must raise water. In your case with your closed loop, that factor contributes zero to your total head loss - it doesn't matter which height the intake and exhaust are within the tank, since the water level is the same. When computing head loss due to vertical rise, the important factor is the water level within the container being pumped into our out of. Since your intake and exhaust are in the same containers, the water level is the same and hence head loss due to vertical raise is zero.
However, head loss can also come from the way the fluid interacts with the pipe you're pushing it through. Without getting in to too many details, you can basically call this frictional loss - i.e. loss due to friction between the water and the inside of the pipe. So, for X feet of pipe -regardless of whether it's vertical, horizontal, etc - you can expect a certain loss. The smaller the pipe, the greater the loss in this case. In addition to that frictional loss, you've got loss from making the water change direction - look at every elbow, tee, etc as a loss point. So, you need to include that in your estimate, as well.
So, you won't have any head loss from actually raising the water up anywhere, but you will have loss from every foot of pipe regardless, and even more loss from each fitting, elbow, tee, etc. Think of it this way - if you put your CL pump right next to the tank and it only had to push water through 2' of pipe, it would generate a lot more flow than if it was a mile away and had to push all that water through 2 miles of pipe.
Hope that makes sense. . .
