เครื่องคำนวณการลดลงของแรงดันในท่อ

The Darcy-Weisbach equation calculates friction pressure drop in pipes: ΔP = f × (L/D) × ρv²/2. It applies to both laminar and turbulent flow — only the friction factor f changes.

It is more accurate and versatile than Hazen-Williams (which only works for water in turbulent flow).

The Colebrook-White equation is implicit — f appears on both sides — so it must be solved iteratively:

1/√f = -2 log₁₀(ε/3.7D + 2.51/(Re√f))

This calculator uses 50 iterations starting from the Swamee-Jain approximation, achieving accuracy better than 0.01%.

Common roughness values (ε):

• Steel: 0.045 mm (new commercial)
• Stainless: 0.015 mm (smooth welded)
• Copper/plastic: 0.0015 mm (very smooth)
• Cast iron: 0.25 mm (new); aged pipes can be 1–3 mm
• Hydraulic hose: 0.005 mm

For aged or corroded pipes, increase roughness by 2–10×.

Each fitting has a K-factor. Sum all K-factors for your system and enter the total in the ΣK field. The minor loss is: ΔP = ΣK × ρv²/2.

Example: A system with two 90° elbows (K=0.9 each), one tee branch (K=1.8), and one check valve (K=2.5): ΣK = 0.9 + 0.9 + 1.8 + 2.5 = 6.1.

Rules of thumb:

• Hydraulic pressure lines: 3–5 bar per 10 m is common
• Hydraulic return lines: 0.5–1 bar per 10 m
• Water supply: 0.1–0.3 bar per 100 m of pipe
• Total system ΔP must not exceed available pump pressure