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Determination of the nominal width

> > Nominal width

What inside diameter is needed for my hose- or pipe line?

How do I determine the nominal width?

The following oil speeds are recommended as reference value:
Suction lines 0,5 ... 1,5m/s
Return lines 2 ... 4m/s
Pressure lines 3 ... 10m/s

Formula for Oil Speed:

Formel 1 > > > Formula (1)

v=Oil Speed [m/s]
Q=Flow rate [l/min]
d=Pipe inside diameter [mm]

Formula for the required Pipe inside diameter:

Formel 2 > > > Formula (2)

Calculation of the required diameter for a hydraulic power units with 20 l/min flow rate with Formula (2):

1. Suction hose

Formel 3  
Formel 4  

The inside diameter for the suction line should be between 17mm and 29mm.
Nominal width 20 or 25 would be chosen.

2. Return line

Formel 5  
Formel 6  

The inside diameter for the return line should be between 10mm and 15mm.
Nominal width 12 would be chosen.

3. Pressure line

Formel 7  
Formel 8  

The inside diameter for the pressure line should be between 7mm and 12mm.
Nominal width 10 would be chosen. An overview of nominal width and inside diameter can be accessed at

Caution: The data about oil speed are viscosity dependent. All informatio are for conventional hydraulic oils at normal oil temperatures! The data is not apllicable for highly viscous oils and extreme temperatures!

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