What are displacement and discharge pressure?
Displacement (also known as volumetric flow rate) refers to the volume of free air delivered by the air compressor per unit time, typically expressed in m³/min or L/s, reflecting the air supply capacity. Discharge pressure is the steady‑state pressure attained by the compressed air at the outlet, measured in MPa or bar, and it determines whether pneumatic equipment can operate properly.
The dynamic relationship between pressure and flow
The actual displacement of an air compressor decreases as the discharge pressure increases. This is because the rising compression ratio leads to increased internal leakage and reduced volumetric efficiency. The rated volumetric flow specified for a particular model at its nominal pressure cannot be directly applied to higher‑pressure operating conditions.
Key considerations in equipment selection
- Determine the system’s minimum operating pressure and peak air consumption;
- Adjust the theoretical requirements by accounting for pipeline pressure drops and altitude correction factors;
- Avoid selecting equipment based solely on rated pressure while neglecting the pressure–flow characteristic curve;
- When multiple units are connected in parallel, verify that the total air delivery meets the actual supply capacity after pressure drop.