Saved Scenario Comparison
Saved results remain in this browser. Compare flow, velocity, pressure, and losses.
| Name | Flow | Velocity | Total loss | Crest pressure | Action |
|---|
Formula Used
Available head: H = z_source − z_outlet Ideal flow: Q = nA√(2gH) Darcy loss: h_f = f(L/D)(v²/2g) Minor loss: h_m = ΣK(v²/2g) Energy balance: H = Σh_f + Σh_m Reynolds number: Re = ρvD/μ Crest pressure head: p_c/(ρg) = p_atm/(ρg) + z_source − z_crest − v²/(2g) − h_suction
The calculator solves the energy balance iteratively. Friction changes as velocity and Reynolds number change. This improves accuracy for practical siphon systems.
How to Use the Calculator
Choose the required calculation mode first. Enter source, outlet, and crest elevations carefully. Use one consistent elevation reference throughout.
Add every active pipe segment and fitting. Select realistic fluid and roughness data. Review warnings before trusting the final design.
Enable drainage for changing tank levels. Define the tank geometry and depth range. Increase simulation steps for smoother results.
Worked Example
| Input | Example value | Purpose |
|---|---|---|
| Source elevation | 2.5 m | Defines the upstream energy level. |
| Outlet elevation | 0 m | Creates 2.5 m driving head. |
| Crest elevation | 4 m | Checks crest vacuum and safety. |
| Pipe | 12 m, 25 mm | Defines friction and velocity. |
| Fluid | Water at 20°C | Sets density, viscosity, and vapour pressure. |
The example models a short water siphon. Entrance and exit losses are included automatically. Actual performance still depends on priming and airtight joints.
Understanding the Results
Ideal flow ignores pipe and fitting resistance. Real flow includes the chosen hydraulic loss method. The difference shows the practical energy penalty.
Crest absolute pressure must remain above vapour pressure. A small margin increases cavitation and separation risk. Atmospheric pressure falls as site altitude rises.
Drain time changes with falling source level. Lower liquid depth reduces available driving head. The simulation updates flow throughout the discharge.
Frequently Asked Questions
What makes a siphon start?
The pipe must be filled with liquid. The outlet must remain below the source surface. Air leaks can break the liquid column.
Can a siphon lift water indefinitely?
No. Atmospheric pressure and vapour pressure limit crest height. Real systems require a generous safety margin.
Which friction method should I use?
Darcy–Weisbach works for many fluids. Colebrook is suitable for turbulent pipe flow. Hazen–Williams is mainly a water approximation.
Why is real flow below ideal flow?
Pipe walls and fittings consume energy. Smaller diameters create higher velocity and losses. Longer pipes also reduce available discharge.
What is a safe siphon velocity?
Acceptable velocity depends on the system. Very high velocity increases noise and losses. Check material and process limits separately.
Why does altitude matter?
Higher altitude lowers atmospheric pressure. This reduces the theoretical crest limit. Cavitation risk therefore rises at elevation.
Can I use this for oil?
Yes, with suitable fluid properties. Enter accurate density, viscosity, and vapour pressure. Confirm chemical compatibility with all materials.
Why can drainage stop early?
The liquid surface may approach outlet elevation. Available head then reaches zero. The siphon can also lose prime first.
Does submerged discharge change results?
It can change the downstream pressure condition. Enter the effective downstream hydraulic level. Detailed installations may need professional modelling.
How accurate are fitting coefficients?
Published coefficients are approximate. Geometry and valve position affect actual losses. Manufacturer data is preferable when available.
Can several siphons run in parallel?
Yes. Enter the number of identical parallel pipes. The calculator divides total flow equally between them.
Engineering and Safety Disclaimer
This calculator provides engineering estimates only. It does not replace site testing or professional review. Hazardous liquids require specialist controls and procedures.