How much does the flow of a pipe get reduced if undersized couplings are used?

[paul_martin]

Hi all first post, thanks for having me!

I am designing a water delivery system to pump purified water from one tank to another over a distance of around 40m. Fastest possible transfer time is the primary goal and so am using the biggest practical hose diameter I can realistically buy which is 1inch

However I am finding it hard to buy 1inch couplings to maintain the diameter all the way through the system so have to resort to 3/4” couplings which at their smallest point have an internal diameter of around 1/2"
I am effectively halving the internal diameter.

I know the internal diameter of the hose is massively important to the flow rate, I think moving from half inch to 1 inch almost trebles the flow rate, but if the internal diameter is reduced just for the couplings at each end how much will this affect the flow rate overall. Is it really worth worrying about?

Looking forward to hearing some of your answers!

[prichmon74]

based on the cross sectional area of smallest portion. So if you 1/2 the diameter you reduce flow to 1/4 as I recall.

[Hudson]

Look harder for 1" couplings. They should be less than a dollar for the PVC type.