Hydraulic Line Velocity & Pressure Drop Calculator

Size hydraulic suction lines, pressure lines, and return hoses to prevent pump cavitation and minimize line friction losses per ISO 4413 standards.

Flow & Line Application

Flow Rate Q (GPM):

Line Service Type:

Hose / Tube Internal Diameter:

Fluid Properties & Line Length

Hydraulic Fluid Viscosity:

Line Run Length (ft):

Fluid Velocity & Friction Drop

Fluid Flow Velocity (V)

-- ft/sec

Total Pressure Drop

-- psi

-- psi per 100 ft

Reynolds Number (Re)

Laminar / Turbulent

Darcy Friction Factor (f): --

Hydraulic Power Loss: -- HP heat loss

Target Velocity Window: 15 - 25 ft/s

Suction lines must strictly adhere to 2 to 4 ft/s to prevent pump cavitation and catastrophic pump failure.

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Frequently Asked Questions

Why must pump suction line velocity never exceed 2 to 4 ft/sec?

Pumps do not suck oil; atmospheric pressure on the reservoir pushes oil into the expanding pump chambers. If suction line velocity exceeds 4 ft/sec, pipe friction creates high vacuum at the pump inlet. This pulls dissolved air out of solution (cavitation), creating imploding vapor cavities that violently pit and destroy pump internals.

What are standard hydraulic hose dash sizes?

Hose dash sizes represent the inner diameter measured in sixteenths of an inch. For example: -04 = 4/16" (1/4" ID), -08 = 8/16" (1/2" ID), -12 = 12/16" (3/4" ID), -16 = 16/16" (1" ID), and -32 = 32/16" (2" ID).

How does oil temperature affect hydraulic pressure drop?

Hydraulic fluid viscosity changes exponentially with temperature. During a cold winter startup at 40°F, ISO 46 oil viscosity can surge from 46 cSt up to 400 cSt, multiplying laminar friction pressure drop by nearly ten-fold and causing sluggish machine response.