Pipe pressure drop calculator

Darcy-Weisbach straight-pipe loss; Darcy friction factor supplied.

fluids-pipe-pressure-drop.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	velocitym/s	lossPa
	0.530516	2110.86
	0.530516	1688.69

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

pressure loss budget2110.86 Pa✓ passes

BASELINE INPUTS

length10 mdiameter20 mmflow10 L/mindensity1000 kg/m^3darcyFactor0.03

CALCULATED

velocity0.53052 m/s

loss2110.9 Pa

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Pipe pressure drop
# Scope: Darcy-Weisbach straight-pipe loss; Darcy friction factor supplied.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

length = 10 m
diameter = 20 mm
flow = 10 L/min
density = 1000 kg/m^3
darcyFactor = 0.03

velocity := 4*flow/(pi*diameter^2) [m/s]
loss := darcyFactor*length/diameter*density*velocity^2/2 [Pa]

check pressure loss budget: loss <= 5000 Pa

scenario alternative: length = 8 m

Calculated from your source · not saved

Baseline · Baseline

pressure loss budget2110.86 Pa ✓ passes

alternative · alternative

pressure loss budget1688.69 Pa ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

velocity: velocity = 4*flow/(pi*diameter^2) [m/s]
loss: loss = darcyFactor*length/diameter*density*velocity^2/2 [Pa]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

length: 10 m
diameter: 20 mm
flow: 10 L/min
density: 1000 kg/m^3
darcy factor: 0.03

Calculated

velocity: 0.530516 m/s
loss: 2110.86 Pa

Assumptions and limits

Darcy-Weisbach straight-pipe loss; Darcy friction factor supplied.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Pipe pressure drop. Inputs: length; diameter; roughness; flow; fluid properties. Outputs: frictional pressure drop; required head. Model scope: Single-phase flow unless explicitly configured otherwise. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: length, diameter, roughness, flow, fluid properties
Outputs: frictional pressure drop, required head
Modes: calculate, compare, sweep
Drawing: Flow network and pressure plot

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS