Why Is the Single-Acting Vane Pump Called a Non-Unloading Pump

Core Reason: Permanent Eccentricity

In a standard single-acting vane pump:

• The cam ring and rotor maintain fixed eccentricity
• Pump displacement remains constant
• Flow is continuously delivered during rotation
• There is no built-in pressure unloading path

Therefore, the pump does not automatically unload under pressure, so it is called a non-unloading vane pump.

Hydraulic Behavior Characteristics

Because there is:

• Only one suction zone
• Only one discharge zone
• Continuous chamber sealing

The pump always outputs flow as long as it rotates.

⚠️ Without external control, system pressure must be regulated by relief valves.