Ok, here is my question. I was recently asked to calculate the PDP on a relay operation. Being the supplying pumper I need to pump 1550 gpm through a 3" with 2 1/2" couplings and a 4" line, the distance was 500'. I came up with a method that I thought would work for calculating the friction loss and I was wondering if this would have worked.

With out a given pump chart with the calculated friction losses for this configuration of a Siamese set up, I originally split the flow in half and calculated the friction loss in each hose section which in-turn had different numbers. I had trouble with this concept because I know if I pumped the 4” at the same pressure of the 3” I would be giving them too much water, which isn’t bad, but it would be too high of pressure.

The method I came up with was to look at the friction loss chart reference the PSI and GPM numbers until the friction loss in 100’ for both sizes was similar enough, within 5-10 psi, and the sum of the two GPM’s equaled 1500.

I brought this theory and method to my training officer and he said that he hadn’t seen that method before and wasn’t sure if it would work or not. Everyone else that I’ve asked couldn’t answer definitively one way or another. Could someone please let me know if this method is flawed or if it truly works? I could supply the numbers for the friction loss if you need them.

With out a given pump chart with the calculated friction losses for this configuration of a Siamese set up, I originally split the flow in half and calculated the friction loss in each hose section which in-turn had different numbers. I had trouble with this concept because I know if I pumped the 4” at the same pressure of the 3” I would be giving them too much water, which isn’t bad, but it would be too high of pressure.

The method I came up with was to look at the friction loss chart reference the PSI and GPM numbers until the friction loss in 100’ for both sizes was similar enough, within 5-10 psi, and the sum of the two GPM’s equaled 1500.

I brought this theory and method to my training officer and he said that he hadn’t seen that method before and wasn’t sure if it would work or not. Everyone else that I’ve asked couldn’t answer definitively one way or another. Could someone please let me know if this method is flawed or if it truly works? I could supply the numbers for the friction loss if you need them.

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