(A) 100 feet of 1/2" plastic pipe with one (1) 90 elbow and one (1) swing check valve:
1) 90 degree elbow = 1.5 feet of straight pipe
2) Swing check valve = 4.0 feet of straight pipe
3) 100 feet of pipe = 100 feet of straight pipe
4) Total equivalent pipe = 1.5 feet + 4.0 feet + 100 feet = 105.5 feet
(B) Assume flow of 5 GPM through 1/2" pipe:
1) Friction loss table for 1/2" pipe shows 22.2 feet loss per 100 feet of pipe. (22.2 feet divided by 100 = .222 loss per foot)
2) In step (A) we determined that the total equivalent feet of pipe to be 105.5 feet.
3) Multiply 105.5 feet X .222 (loss per foot) = 23.42 feet
Total friction loss in this system = 23.42 feet