Low-pressure straight-pipe approximation
Pneumatic line pressure loss
Inputs
User-entered actual volumetric flow at the stated upstream condition; standard-flow conversion is excluded.
Declared constant straight-pipe inside diameter.
Declared straight run length; fitting and network equivalents are excluded.
User-entered Darcy friction factor for the stated condition; it is not derived or selected here.
User-entered density at the stated upstream condition; density variation is excluded.
Declared upstream absolute pressure used only for the ten-percent approximation guard.
Results
Declared pipe flow areaA
555.72
Mean upstream-density air velocity
17.995
Declared-density Darcy major lossΔp
20.39
Major loss / upstream absolute pressure
3.3984
%A = πD²/4 · v = Q/A · Δp = f(L/D)(ρv²/2) · guard: Δp/p₁ < 10%
A first-pass number, not a code check, certification, or approval. Read the method and its limits below. What this is and is not.
Nearby: Hydrostatic pressure · Flow continuity · Pipe mean velocity · Bernoulli equation
Method
Formula, when it applies, and when it does not
Calculate upstream-density Darcy major loss and mean velocity for one straight compressed-air pipe section, guarded below ten percent upstream pressure loss.
A = πD²/4 · v = Q/A · Δp = f(L/D)(ρv²/2) · guard: Δp/p₁ < 10%
When
- Straight constant-ID pipe only
- User-entered Darcy friction factor and density
- Calculated loss below 10% of upstream absolute pressure
Don’t
- This is a low-pressure straight-pipe compressed-air approximation using user-entered upstream density and Darcy friction factor. It is valid only while the calculated major loss remains below 10% of upstream absolute pressure. It excludes fittings/minor losses, networks, elevation, density/temperature variation, choked flow, compressor or valve selection, line sizing, capacity, safety, and approval.
Crane TP-410, Flow of Fluids Through Valves, Fittings and Pipe