Water jet pump
A water jet pump is a simple jet pump in which water is used as the driving medium in a Venturi nozzle . Their invention is mostly attributed to Robert Wilhelm Bunsen .
This technique is often used to provide a vacuum to produce or to liquids or gases ERS suck . It is used in water supplies to suck in gases such as oxygen or air and mix them with the water.
Structure and functionality
In the Venturi nozzle, the dynamic pressure (back pressure ) is maximum and the static pressure is minimum at the narrowest point of the pipe . The speed of the water increases in proportion to the cross-section when flowing through the constricted part, because the same amount flows through everywhere. At the same time, the pressure drops proportionally in the intake pipe, which is located exactly in the narrow part.
If the flow rate fluctuates, the negative pressure also changes . If the inflow is stopped completely (by carelessly closing the tap), the negative pressure sucks water into the apparatus, which is referred to as kickback.
The minimum achievable pressure corresponds to the vapor pressure of the water and is therefore temperature-dependent, it is 6 hPa at 0 ° C ( see also: Material properties of the saturation vapor pressure depending on the boiling and sublimation temperature ).
The suction power is directly proportional to the water flow. A suction pump can suction up to the respective geodetic suction height , so it is not suitable for pumping out of deep shafts.
Areas of application
Water jet pumps used in laboratories are usually made of glass, plastic or metal and are connected to a water tap by means of a hose or, more often, a screw connection. Because of the high water consumption, the uncomfortably high noise level and the pollution of the wastewater with possibly high proportions of organic solvents, the water jet pumps are increasingly being replaced by electrically operated vacuum pumps . When using water jet pumps, a safety wash bottle ( Woulfe bottle ) must always be attached because of the risk of kickback between the apparatus and the pump .
Since the pump itself does not need a drive, no power connection or an internal combustion engine is necessary. The pump can therefore also be operated in potentially explosive areas.
In the fire brigade , the water jet pump is a water-bearing fitting for drawing water and, in the past, was often used for pumping empty basements that were full.
Trivia
The air intake to reach a blue flame with a Bunsen burner is based on the same principle.
literature
- Ludwig Prandtl, Oskar Tietjens: Fundamentals of Hydro- and Aerodynamics. Dover 1934, page 243.
Individual evidence
- ^ Walter Wittenberger: Chemical laboratory technology. 7th edition. Springer, Vienna 1973, ISBN 3-211-81116-8 , pp. 258-259.