3.3.2. Suction capacity - output


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Fig. 3.25: Suction rate and free air delivered
Suction rate - Output
Stroke volume flow - Volume flow

The suction rate (stroke volume flow) is a calculated size for piston compressors. It is the product of cylinder capacity, compressor speed (number of strokes) and the number of intake cylinders. The stroke volume flow is given in l/min, m³/min and m³/h .

The output (free air delivered FAD) is measured according to VDMA Unit Sheet 4362, DIN 1945, ISO 1217 or PN2 CPTC2.

The ratio of output to induction rate is the volumetric efficiency rate.BR><BR>


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Fig. 3.26: Clearance area
Clearance area

The clearance area is a specific dimension located between the top dead centre of the piston and the bottom edge of the valve.

The clearance area includes:
    • Design tolerances
    • Cavities in the valves and valve seats
    • Individual design considerations

During the down stroke of the piston the air in the compression expands to atmospheric pressure. Only at this stage and during the continued downstroke of the piston is air sucked in from outside.

The difference between the suction rate and the output occurs because during suction the pressure of the air already drops in the inlet filter, leakages also occur, the air sucked in heats up and re-expansion occurs in the compression space.