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TECHNICAL DOCUMENTATION

PRINCIPLES OF PNEUMATICS

PRESSURE:

The ratio between a force and the surface on which it acts.

ATMOSPHERIC PRESSURE:

Equivalent to the pressure exerted on a surface at sea level at 20°C and with 65% humidity:

10.33 m H

2

O; 760 mm Hg; 1.013 x 10

5

Pa.

ABSOLUTE PRESSURE:

The pressure above the absolute zero value - pressure 0 = absolute vacuum.

GAUGE PRESSURE:

The pressure referring to ambient atmospheric pressure: it is normally indicated by the pressure

gauges used in pneumatic circuits.

Pressure read

on gauge (6 bar)

Atmospheric pressure

Absolute vacuum

Gauge pressure

(6 bar)

Absolute pressure

(7 bar)

Gauge pressure = (absolute P) - (atmospheric P.)

UPSTREAM PRESSURE:

Pressure of the compressed air at the pneumatic component inlet.

DOWNSTREAM PRESSURE:

Pressure of the compressed air at the pneumatic component outlet.

ΔP PRESSURE DROP:

Difference between upstream and downstream pressure.

FLOW RATE:

The volume of air passing through a given section in a unit of time.

In pneumatics, the volume unit of measurement is Nl (Normal litre).

In practice it represents the volumetric capacity of the air referring to ambient atmospheric pressure.

E.g. in a conduit of a given section, there is a mass flow of 1 litre of air (1 dm

3

) at 7 bar absolute

pressure. This value expressed as volume of air corresponds to 7 litres of air (7 dm

3

) at the ambient

atmospheric pressure (1 bar).

1 dm

3

7 bar

absolute

1 dm

3

1 bar

absolute

1 dm

3

1 bar

absolute

1 dm

3

1 bar

absolute

1 dm

3

1 bar

absolute

1 dm

3

1 bar

absolute

1 dm

3

1 bar

absolute

1 dm

3

1 bar

absolute

Mass flow

Volumetric flow rate

(referring to absolute pressure)

• With the same pressure, the flow rate is directly proportional to the port cross section.

• With the same cross section, the pressure is directly proportional to the flow rate.

• Without a ΔP (difference between upstream and downstream pressure), there can be no flow rate.

PASCAL’S LAW:

A confined fluid transmits externally applied pressure uniformly in all directions.

Density of air, measured to 20°C to the atmospheric pressure: 1.275

kg

m

3

TECHNICAL DOCUMENTATION