Side channel pump
The side channel pump is a niche product between positive displacement pumps and centrifugal pumps .
history
The technical age of this pump principle began at the end of the 19th century. The invention of a water ring pump had the purpose of conveying air , gases and liquids . In the 1920s, the side channel pump, which is still indispensable in many areas of application around the world, developed from this. SIHI and SERO pioneered the first developments and are still the innovation drivers of this type of pump today. The SIHI company applied for a patent for the actual side channel hydraulics in 1949 and received this patent in 1950.
properties
The special characteristics of the side channel pump:
- it has an automatic suction capacity
- it has the ability to transport gas undamaged
- it has its highest power requirement with the smallest flow rate
- the steep QH curve of the characteristic is particularly suitable for pressure-dependent circuit control
- the narrow gaps do not allow any abrasive components in the delivery liquid
In the suction process, side channel pumps initiate the pumping of liquid with the automatic evacuation of the suction line, with the gas contained in the suction line being sucked off and the pumping liquid rising to the pump. It can work as a liquid ring vacuum pump for a short time and is therefore also referred to as a rotating displacement pump . Similar to the operating principle of the liquid vacuum pump, a rotating liquid ring creates a displacement effect, in that the remaining amount of liquid (also called auxiliary liquid) enters and exits the star-shaped impeller like a piston with each rotation and the eccentrically arranged side channel. Due to the centrifugal effect, the liquid collects in the outer area of the side channel and the impeller cells and thus forms the liquid ring that is important for the suction process. The gas is concentrated in the inner area.
The operation of the side channel pump as a pure vacuum pump is only possible for a limited time, however, because the auxiliary liquid is increasingly heated and would eventually evaporate without cooling.
In addition to the self-priming capability, the side channel pump has the further advantage of pumping large gas flows. In process engineering systems, a pump is very often required at least temporarily to convey gases and vapors from the process without interrupting the flow. Normal centrifugal pumps are only able to convey a limited proportion of gas with the medium. Even with relatively small proportions of gas, the pumping of liquid with these pumps can stop completely.
The side channel pump does not have any effect on large proportions of gas in the liquid and is pumped without any external auxiliary equipment.
After the suction, the flow process automatically changes from displacement via foam-like mixture delivery to pure liquid delivery. When the side channel pump is completely filled with the pumped liquid, it can be regarded as a centrifugal pump .
The special type of flow through the side channel steps with deliberate deflections gives the conveyed medium a much higher energy content than is possible with conventional radial wheels. The medium circulates helically many times within the individual vane spaces on its way from the inlet to the outlet from the conveying channel. The pressure build-up results from the sum of the individual pulses during the cycle. One therefore speaks of an internal multi-stage effect. The five to ten times higher pressure factor can be seen as an enormous advantage over “normal” centrifugal pumps.
The low drive speed of n = 1450 / min, made possible by the high pressure factor, reduces the NPSH value even further compared to a high-speed pump. The slow speed also has the advantage that mechanical loads, part load behavior and noise behavior are better controlled and the service life is also increased.
The lower the specific speed of a pump, the better its suction capacity and the lower the risk of cavitation . The side channel pump is considerably less sensitive to cavitation than a radial centrifugal pump when the vapor pressure is variable.
application
The side channel pump is used in the range of small to medium flow rates (Q up to 35 m³ / h) and medium to high delivery heights (H up to 400 m).
The pumped medium and the operating conditions determine the choice of materials and seals. The range of materials ranges from gray cast iron to high-alloy stainless steels. Single and double-acting mechanical seals are available for shaft sealing . The pump can be driven with a permanent magnetic synchronous coupling (magnetic drive) or with canned motors without any shaft seal.
If the side channel pump is preceded by a radial impeller stage, extremely low NPSH values can be achieved. Such multi-function pumps are particularly well suited to conveying liquids close to the boiling point, such as condensate , liquid gases , hydrocarbons , aerosols or refrigerants .
See also
literature
- Faragallah, WH (Editor); Side channel flow machines . Publishing house and picture archive WH Faragallah, 1992 ISBN 3-929682-01-X
- Faragallah, WH (Editor); Centrifugal pump designs: state of the art and internet references . Publishing house and picture archive WH Faragallah, 2006 ISBN 3-929682-41-9
- Ignatowitz, Eckhard, Dr.-Ing., Chemietechnik , Verlag Europa-Lehrmittel, 2007 ISBN 978-3-8085-7048-7