How to calculate pressure drop and friction losses in a pipe

A quick look at this WIKI calculator (below) will convince you that this is more voodoo than science and any reasonable engineer or designer must learn to rely upon educated estimates based upon prior research.

In short, gravitational lift and length of pipe are of primary importance in the estimate of head pressure loss with fittings, valves and individual water features being less significant to the overall equation. We see so many filters and pump combinations in the field thrown together seemingly willy-nilly with no reasonable attempt to match or optimize anything.

Wikipedia.org: Weisbach equation

As an example, I met with a customer recently who complained of poor suction from the skimmers. An examination of the filter system indicated a standard duty 2hp pump capable of 110 gpm, a 48 square foot DE filter with a design flow rate of 96 GPM, a 1.5 inch multiport valve and 1.5 inch filter interconnects. Let’s take a look at these individual components and see if we can diagnose the problem.

 Standard Hayward 2hp Super pump flow rate 110 gpm (@30 feet of head) Hayward 4800 DE filter design flow rate 96 gpm 1.5 inch Hayward multiport valve design flow rate 60 gpm (@20 feet of head) 1.5 inch filter interconnects maximum flow rate 44 gpm less with elbows