Sizing of Suction Hoses

Suction hoses play a crucial role in the reliable operation of hydraulic pumps:

Calculation and Installation of a Suction Hose for Hydraulic Pumps

1. Purpose of the Calculation

It must be ensured that:

• the flow velocity in the suction hose is sufficiently low,
• no vacuum is created that could cause cavitation,
• the hose is adequately sized to accommodate the pump’s delivery volume.

2. Calculation Basis

Two parameters are relevant for the calculation:

• v = flow velocity [m/s]
• Q = flow rate [m³/s]

3. Example Calculation

Example: A hydraulic pump has a maximum flow rate of Q = 60 l/min.

→ The recommended flow velocity v for suction hoses should be between 0.5 – 1.2 m/s.

We choose 0.8 m/s

→ Calculate hose diameter:

d = square root of (Q/v) * 4.607 ≈ 39.9 mm

Result: At least a DN 40 (1 ½") hose is required

4. Practical Installation Tips

• Use an oil-resistant, vacuum-proof hose with a smooth inner wall
• Avoid narrow sections or sharp bends
• Keep the hose as short and straight as possible
• Install the pump below the oil level if possible
• Use filters with low flow resistance only (coarse mesh: 125–250 µm)

5. Important Notes

• Maximum permissible pressure loss on the suction side: 0.2 bar
• Tank should provide a calm return flow
• Bleed the pump before initial operation (never run dry)
• The calculation assumes adequate oil viscosity. If oil viscosity is too low (e.g., in winter), cavitation can still occur even with a properly sized suction hose.