Mechanical & Fluids Calculation guide Calculate a value

Where the pressure in a pipe line actually goes

Separating frictional loss from fitting loss, and why small bore runs lose far more than intuition suggests.

The engineering question

The pump has the pressure but the far end does not. How much is lost in the pipe itself, and how much in the fittings?

Worked example

The figures below were produced by running the Pipe Fitting Loss Calculator with the same inputs — during the build, from its authoritative engine.

Results
Head loss	0.4893 m
Pressure drop	4.8 kPa
Velocity head	0.2039 m
Equivalent straight length	12 m
Assessment	Through a K = 2.4 fitting the head loss is 0.49 m (≈ 5 kPa water). Equivalent straight length ≈ 12.0 m at f = 0.02.

Velocity head is V²/2g, and the loss is K times that.
Two standard elbows and a gate valve is a K of roughly 2.4.
The equivalent straight length converts the loss into pipe metres, which makes it comparable with the run itself.

Sanity check

Doubling the velocity quadruples the loss. A small velocity increase is rarely a cheap way to solve a pressure problem.

Tools for this problem

These are the EngiMetric calculators that compute the numbers in this topic. Each one shows its formula, its units and its limits rather than returning a bare result.

Pipe Fitting Loss Calculator Head loss, pressure drop and equivalent length for a pipe fitting from its K-value and flow velocity.

References & standards

Crane TP-410 — loss coefficients
ASME B31.3 — pressure drop criteria

Where the pressure in a pipe line actually goes

The engineering question

Worked example

Sanity check

Tools for this problem

References & standards

Related problems

Why a pump is cavitating and what NPSH margin it needs

Finding the duty point instead of guessing a pump size