Compressed Air Receiver Volume

Anyone laying out a compressor room learns early that the tank sits there to protect the motor, and only incidentally to hold air. A load-unload piston machine starts and stops all day, and the motor maker caps that count: ten, twenty, sometimes thirty starts an hour depending on frame size. A cramped receiver makes the pressure switch cycle every couple of minutes, the winding gets no time to shed inrush heat, and the overload trips mid-shift. The field symptom is unloading over and over even while demand stays light.

V = 15 × Q × Pa ÷ (N × ΔP). Q is free air delivery in cubic metres per minute, referred to suction conditions; N the maximum starts per hour the motor accepts; ΔP the gap between load and unload pressure, almost always 1 to 2 bar; Pa the local atmospheric pressure in bar, 1.013 at sea level and near 0.9 at a thousand metres. Pa belongs in there because delivery is quoted at atmospheric conditions while the vessel stores mass. The constant 15 is 60 minutes over four: worst case, demand equals half the capacity, so half the flow fills the tank during half of every cycle.

The result applies to machines running load-unload or start-stop. A variable speed drive follows demand without restarting, and its receiver comes from a different criterion, pressure stability. The number also ignores peak draw: if the line feeds a press that wants 3 m³ in ten seconds, size the vessel by holdup time and expect something much larger. Two unit slips turn up constantly — delivery in m³/h typed into a m³/min field, which inflates the tank sixtyfold, and pressure in kPa or psi where bar belongs.