Lexicon DIY-Knowledge





Physically speaking, pressure is force per surface unit. The force is perpendicular to the surface. The general pressure is measured in Pascal (Pa).

1 Pascal = 1         

Atmospheric pressure is measured in bar, whereby 1 bar v 10 N/cm2 v 105 Pa.

Recently, atmospheric pressure has also been measured in Hecto-Pascal (hPa).

1 hPa = 100 Pa

1 hPa =          bar = 1 mbar

The technical specifications for air tools are based on an operating pressure of 6.3bar or 90psi in accordance with ISO2787.

In the case of pumps, e.g. high-pressure cleaners, pressure is a measure of the operative capability.

The pressure generated in pressure pumps is measured in units above the standard atmospheric pressure, i.e. it is over 1 bar = 10 N/cm2 (overpressure). The pressure at the intake valve of a suction pump is below 1 bar (vacuum or negative pressure) and can be measured in meters of water column (mWC).

1 mWS ~ 0,1 bar

For instance, a high pressure cleaner with a suction capacity of 2 mWC is capable of taking in water from a water reservoir up to 2 m below the intake valve of the pump.

The same physical factors apply to vacuum cleaners. Here the suction capacity is also specified in mWC. It should be noted that the diameter of the suction hose, respectively of the intake of the suction nozzle has an influence on the effectiveness of the vacuum. (See also Water column)