Calculate pressure loss in hydraulic lines using Hagen-Poiseuille or Darcy-Weisbach formulas.
Pressure drop along a pipe consumes pump power and reduces actuator pressure at the load. This calculator computes ΔP from pipe length, inside diameter, flow rate, fluid density, and viscosity using the Darcy–Weisbach equation, automatically applying the laminar (Hagen–Poiseuille) or turbulent (Swamee–Jain) friction factor based on Reynolds number. It is the most-used tool in hydraulic-system design after force and flow calculations.
ΔP = f × (L / D) × (ρ × v² / 2) where f is the Darcy friction factor, L the pipe length, D the inside diameter, ρ the fluid density, and v the mean velocity. The friction factor depends on flow regime: laminar f = 64 / Re for Re < 2,300; turbulent f from the Swamee–Jain explicit form 1/√f = −2 × log₁₀ (ε/3.7D + 5.74/Re^0.9) for Re > 4,000. Roughness ε is 0.0015 mm for drawn tubing, 0.046 mm for commercial steel, 0.26 mm for galvanized. Total system pressure drop is the sum over each straight section plus the equivalent-length of fittings — the equivalent-length calculator handles the fittings.
A system designer running 80 lpm of ISO VG 32 through 8 m of 16 mm pressure tube computes ΔP = 4.5 bar and adds it to the load pressure when sizing the pump, ensuring 250 bar at the cylinder when the pump-relief is set to 255 bar.
A maintenance engineer investigating slow actuator speed at the end of a 30 m return line computes 12 bar drop at 80 lpm, replaces the 12 mm hose with 16 mm tube, and recovers actuator speed to commissioning specification.
A power-unit builder selects a return-side cooler with 0.6 bar drop at 100 lpm; the calculator confirms total return-line drop (cooler + filter + pipe) stays below the 2 bar limit for the pump-shaft seal.
Re < 2,300, which usually means hydraulic suction lines and very slow oil flow. Above Re = 4,000 use the turbulent form. In the transition band (2,300-4,000) the result is uncertain; treat as turbulent for safety.
Yes. Oil viscosity drops sharply with temperature — ISO VG 46 at 40 °C is 46 cSt, at 60 °C only ~22 cSt. Lower viscosity means lower friction factor in laminar flow but possibly higher Reynolds number, so always compute at expected operating temperature.
Roughness ε is the mean height of the pipe wall asperities. Manufacturers publish it: 0.0015 mm for drawn steel tube, 0.025 mm for new commercial pipe, 0.15-0.30 mm for galvanized.