Geodetic suction height

In pumps, the geodetic suction head is the height between the surface of the liquid level on the suction side and the center of the impeller (pump inlet).

use

Basically, higher than the respective geodetic suction height can not be sucked in with a lot of drive power. It would only be vented above the column of liquid, i.e. gaseous water molecules would be sucked off and a vacuum would be created.

If larger suction heights have to be overcome, a delivery pump is used (also known as a feeder pump or deep suction). This builds as a vacuum pump a pressure to sufficient to promote water to a higher stationary, sucking pump. There are especially submersible pumps and turbo submersible pumps , in an emergency water pump .

Maximum suction lift

Theoretically

The theoretically maximum achievable geodetic suction height depends on the air pressure (and thus the height of the location) and the water temperature (density of the medium). At normal pressure (1013 mbar = 1013 hPa) at sea ​​level and 4 ° C water temperature, the maximum geodetic suction height is 10.33 m.

Derivation

The basic hydrostatic equation :

${\displaystyle p_{1}=p_{0}+\rho \cdot g\cdot h}$

is adjusted according to the height : ${\displaystyle h}$

${\displaystyle \Rightarrow h={\frac {p_{1}-p_{0}}{\rho \cdot g}}}$

With

• ${\displaystyle \rho }$: Density of the liquid (here water)
• ${\displaystyle g}$: Gravitational acceleration
• ${\displaystyle p_{1}}$: Air pressure that acts on the liquid column from the outside (on the surface of the liquid level on the suction side)
• ${\displaystyle p_{0}}$: Pressure by suction above the medium (in the middle of the impeller / at the pump inlet).

It turns out

${\displaystyle h={\frac {1{,}01325\cdot 10^{5}\,\mathrm {Pa} -0\,\mathrm {Pa} }{1000{\frac {\mathrm {kg} }{\mathrm {m} ^{3}}}\cdot 9{,}81{\frac {\mathrm {m} }{\mathrm {s} ^{2}}}}}=10{,}33\,\mathrm {m} }$

At higher altitudes, with lower air pressure , the maximum geodetic suction height decreases accordingly. ${\displaystyle p_{1}}$

Practically achievable suction height

In practice, the maximum suction height is reduced by various factors:

• the flow resistance in the suction line and pump housing,
• the uneven flow conditions in the pump mechanism, which lead to locally occurring vacuum and cavitation ,
• the temperature of the medium, as a vapor pressure above zero  Pascal ( ) causes vapor to form earlier . ${\displaystyle p_{0}>0}$

These influences mean that in practice a maximum suction height ( manometric suction height ) of 7 to 7.50 m can be expected.

The suction head must be observed with all pumps, especially with centrifugal pumps , as cavitation problems arise here even before a maximum suction height is reached.

See also

• Head

literature

• Hans Schönherr: Die Roten Hefte, Heft 44a - Pumps in the fire brigade: Part I: Introduction to hydromechanics, mode of operation of centrifugal pumps . 4th edition. Kohlhammer, Stuttgart 1998, ISBN 978-3-17-015172-7 .
• B. Schueler: Machinist training for fire brigades . 7th, completely revised edition. G. Schueler, Celle 2005, ISBN 3-929137-06-2 .

Individual evidence

1. ↑ Training of volunteer fire brigades - machinist for fire engines (2002), Neckar-Verlag, p. 18
2. ↑ ^{a b} Water pumping over a long wake-up period, "Einsatzpraxis" series, ECOMED, ​​page 156
3. ↑ Extinguishing water supply, series “Fachbücherei Brandschutz”, State Publishing House of the German Democratic Republic, 1973, page 109