Tank to Pump

Formulas

Friction Loss Formula

The friction loss formula multiplies a hose's coefficient by the flow squared by the length to estimate the pressure a lay consumes. Because the flow term is squared, friction loss is driven mostly by how much water is moving.

The formula combines three things: the coefficient that captures the hose's diameter and roughness, the length of the lay, and the flow — entered as its square. Holding the hose and length fixed, doubling the flow roughly quadruples the loss.

It is the engine behind every pump discharge pressure calculation and the laminated reference cards. The squared flow term is the single most important idea: friction loss is a flow problem first and a hose problem second.

Formula

FL = C × Q² × L

C = hose coefficient (set by the diameter); Q = flow in hundreds of gallons per minute; L = length in hundreds of feet. Coefficients vary by department — treat the result as a training estimate.

Common questions

What is the friction loss formula?
The friction loss formula is FL = C × Q² × L: the hose coefficient times the flow squared times the length. Because the flow term is squared, friction loss is driven mostly by how much water is moving.
Why is the flow term squared in the friction loss formula?
Because the pressure lost to turbulence rises roughly with the square of the velocity. In practice that means doubling the flow through a given line roughly quadruples the friction loss — the single most important habit the formula teaches.

Where this shows up

See also