Question 1

When does Hazen-Williams break down?

Accepted Answer

It's calibrated for water at 60 °F in turbulent flow (Re > 4,000). Use Darcy-Weisbach for non-water fluids, very cold water, or laminar flow.

Question 2

Why is the exponent 1.852 and not 2?

Accepted Answer

Empirical fit to turbulent-water data. Doubling flow more than triples head loss because the exponent is between 1 and 2.

Question 3

How do I convert head loss to psi?

Accepted Answer

Divide feet of head by 2.31. e.g. 23.1 ft head = 10 psi.

Question 4

Do I need to add fittings?

Accepted Answer

Yes for short runs. Use AWWA M11 equivalent-length tables — a long-radius 90° elbow on 8-inch pipe adds ~14 ft of equivalent pipe length.

Hazen-Williams Head Loss Calculator