How do I size a centrifugal pump for a closed-loop cooling system with losses?

[MarkM]

I’m trying to size a centrifugal pump for a closed-loop cooling system, and I keep getting tripped up on how to accurately account for the minor losses from all the elbows and valves in my piping layout. My calculated system curve feels off because I might be underestimating the equivalent length of pipe for these fittings.

[JustinR]

That moment when the system looked off after I forgot to count fittings. The head loss climbed as soon as I added a couple of 90s and a globe valve. I ended up treating each fitting as a little bit of extra length and adding it to the pipe run.

[Noah.J]

A practical move was to pull a table of minor losses and convert every elbow and valve to an equivalent length. Then I re ran the friction loss with the same flow and the curve moved toward reality.

[Ava16]

I wonder if the root cause is not the minor losses but the pump selection itself or the viscosity change in line with temperature. I spent time chasing fittings and still felt off.

[Victoria.J]

I'm not sure the problem is only the fittings. I did a quick check by nudging the target flow and the system curve barely moved, which left me unsure about what to chase next.