For vertical U-tube, Δh is the vertical difference of manometric fluid.
Inclined mode uses h = L · sin(θ). Angle is from horizontal.
Pick a preset or enter a custom density.
Used for liquid differential or gauge versus a liquid reference.
Change for local gravity or other planets if needed.
Results
Δh (vertical) [m]—
ΔP [Pa]—
ΔP [kPa]—
ΔP [bar]—
ΔP [psi]—
Head in water [mmH2O]—
Head in water [inH2O]—
Head in mercury [mmHg]—
Head in process fluid [m]—
Equations: For same-liquid differential:
ΔP = g · Δh · (ρm − ρp). For gas lines: ΔP ≈ g · Δh · ρm. Inclined tubes use Δh = L · sin(θ).
Reverse Solver
m
Uses current ρm, ρp, g and application mode.
Runs
| # | Δh [m] | ρm | ρp | g | ΔP [Pa] | kPa | psi | mmH2O | mmHg |
|---|
Friction-Loss Helper with Roughness & Size Presets
Estimate straight-pipe friction loss and compare with your manometer reading.
m
Overwrites automatically if “Lock ε to material” is enabled.
Applies the **inside diameter** to D below. DN mapping approximates to nearest NPS.
Velocity V [m/s]—
Reynolds Re [-]—
Friction factor f (Darcy)—
ΔPfric [Pa]—
ΔPfric [kPa]—
ΔPfric [psi]—
Equivalent Δh (manometer) [m]—
Equivalent head in water [mmH₂O]—
Per length ΔP/L [Pa/m]—
Δh conversion uses current manometer settings (ρm, ρp, g, application mode).
Mini Moody Preview
Shows laminar line and turbulent curve for current relative roughness ε/D. Dot marks your current Re,f if computed.
Formula used
For a U-tube with manometric fluid density ρm and process fluid density ρp above each leg, with vertical reading Δh and gravitational acceleration g:
ΔP = g · Δh · (ρm − ρp)when both taps contain the same liquid of density ρp at the same elevation.ΔP ≈ g · Δh · ρmfor light gases in both lines where line density is negligible compared with ρm.- Inclined manometer: the measured length along the tube is L at angle θ from horizontal; the vertical difference is
Δh = L · sin(θ). - Friction helper:
Re = ρVD/μ,f = 64/Reif laminar; otherwise Swamee–Jain:f = 0.25/[log10(ε/(3.7D)+5.74/Re^0.9)]^2. Pressure lossΔP = f·(L/D)·(ρV²/2). - Moody preview: plots f vs Re for current ε/D alongside the laminar line.
Assumes single-phase, incompressible flow for friction calculations and straight pipe without fittings. Add allowances for fittings separately if needed.
How to use
- Select Reading mode. For inclined tubes, enter L and θ.
- Choose Application: gas differential, liquid differential, or gauge versus atmosphere.
- Pick or enter ρm and, when applicable, ρp. Set g.
- Click Compute to get pressure and head in common units.
- Use Reverse Solver to find the required reading for a target pressure.
- Open Friction-Loss Helper, choose a material, optionally lock ε, then apply a size preset (NPS/DN + Schedule) to set D.
- Compute friction loss. Update the Moody preview to visualize f versus Re.
- Use Add to Runs then export as CSV or PDF.
Example data
| Scenario | Mode | Δh | Unit | ρm | ρp | g | Action |
|---|---|---|---|---|---|---|---|
| Air differential, mercury manometer | vertical | 50 | mm | 13550 | 0 | 9.80665 | |
| Water differential, mercury manometer | vertical | 120 | mm | 13550 | 998.2 | 9.80665 | |
| Gauge versus atmosphere, glycerin manometer | vertical | 8 | cm | 1260 | 998.2 | 9.80665 | |
| Inclined tube, air differential | inclined | 200 | mm | 13550 | 0 | 9.80665 |
Click Load to populate the form. For the inclined example, angle θ = 20° is applied.
FAQs
Use the density of the liquid filling the taps and lines. For gas lines, the line density is negligible compared to manometric fluids, so the gas mode approximation is appropriate.
Measure the length along the tube and multiply by the sine of the inclination angle from horizontal to obtain the vertical head difference used in the equations.
Yes. Fluid density varies with temperature. If accuracy is important, use densities at the measurement temperature or select fluids with well-characterized density curves and apply appropriate corrections.
In narrow tubes, surface tension may curve the meniscus and bias readings. Use larger bore tubes and read at consistent meniscus positions, or apply empirically determined corrections if needed.
Properly used manometers are highly repeatable for low to moderate pressures. Accuracy depends on scale resolution fluid density certainty alignment and temperature stability. Electronic transmitters are better for dynamic or remote applications.