Pipes

When the tube diameter is to small the flow velocity is increased which results in turbulence, increased temperatures and a pressure reduction. This then results in an increased energy demand for the entire system and increased conditions (temperature of the fluid, cavitation). This can result in premature wear and tear of the system.

A tube diameter that is to high increases the stress on the system and increases costs. We recommend to take the following flow velocities into account in hydraulic systems:

The following formula can be used in order to determine the inside diameter of the tube:

\[\text{Inner diameter [mm]} = 4.61 * \sqrt{\text{Flow [l/min]} \over \text{Flow speed [m/s]}}\]

Section "Permissible pressures for stainless steel tubes" specifies the nominal pressure in relation to the tube wall thickness. The nominal pressure is calculated with the following formula:

$$p = 10 K * ln({DA \over DI}) * {1 \over S} \text{[bar]}$$

K: Tensile Strength [N/mm2]
DA: Ø Outside [mm]
DI: Ø Inside [mm]
S: Safety Correction Value

This formula is used in DIN ISO 10763 and is takes the tangential forces on the inside of the tube into account. Using DIN ISO 1073 in general results in reduced nominal pressures compared with DIN 2413. Using DIN ISO 10763 is recommended due to the fact that the results are more precise which is essential for a 4-fold system safety.

• A reliable tube system assembly can only be given when seamless precision steel tubes type St 37.4 or St 52.4 (steel) or e.g. 1.4571 (stainless steel) are used. Take DIN 2391-1 into account for tolerances.
• Bend tubes correctly (maintain roundness, stick to bending radius limitations)
• Keep temperature range in mind (e.g. higher temperatures reduce the nominal pressure rating of stainless steel tubes)
• Keep thermal expansion of the tube in mind
• Pay attention to external conditions such as tube weight

Permissible pressures for stainless steel tubes, 1.4571

(calculated values in accordance with DIN ISO 10763 , safety correction value S = 4)