Fig. 1.17:
Working volume flow and volume flow | Volume flow  [l/min, m³/min, m³/h]
The volume flow describes the volume (l or m³) per unit of time (minute or hour).
A distinction is made between the working volume flow (induction rate) and the volume flow (output rate) of a compressor.
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Working volume flow  Wor [l/min, m³/min, m³/h]
Induction rate
The working volume flow is a calculable quantity on piston compressors. It is the product of the cylinder size (piston capacity), compressor speed (number of strokes) and the number of cylinders working. The working volume flow is given in l/min, m³/min or m³/h.
 Wor = Working volume flow [l/min]
A = Cylinder area [dm2]
s = Stroke [dm]
n = Number of strokes [1/min] (compressor speed)
c = Number of working cylinders
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Fig. 1.18:
Cylinder movement |
Volume flow  [l/min, m³/min, m³/h]
Output rate
The output rate of a compressor is normally declared as the volume flow.
In contrast to the working volume flow, the volume flow is not a calculated value, but one measured at the pressure joint of a compressor and calculated back to the induction state. The volume flow is dependent on the final pressure relative to the induction conditions of pressure and temperature. This is why when calculating the induction state the measured volume flow to induction pressure must be "relaxed" and to induction temperature it must be "re-cooled".
The volume flow is measured according to VDMA 4362, DIN 1945, ISO 1217 or PN2 CPTC2 and given in l/min, m³/min or m³/h. The effective volume flow, i.e., the output that can actually be used, is an important consideration for the design of a compressor. Volume flows can only usefully be compared when measured under the same conditions. This means that the induction temperature, pressure, relative air humidity and measured pressure must match. |
Volume flow (0°C) + 8% = Norm volume flow (20°C)Fig. 1.19: Norm volume flow |
Norm volume flow  Norm [Nl/min, Nm3/min, Nm3/h]
As with the volume flow, the norm volume flow is also measured.
However, it does not refer to the induction state, but to a theoretical comparative value. With the physical norm state the theoretical values are:
Temperature = 273,15 K (0 °C)
Pressure = 1,01325 bar (760 mm HG)
Air density = 1,294 kg/m3 (dry air) |
0 barabs 8 barabs | Operating volume flow  Operat [Ol/min, Om3/min, Om3/h]
The operating volume flow gives the effective volume flow of compressed air.
To be able to compare the operating volume flow with the other volume flows, the pressure of the compressed air must always be given in addition to the dimension Ol/min, Om³/min or Om³/h. |
Fig. 1.20: Operating volume flow |  |