Where are self-priming pumps used?
Centrifugal pump: structure, function
Synonym (s): centrifugal pump, centrifugal pump, centrifugal pumps, radial centrifugal pumps, centrifugal pump
Structure and function of the centrifugal pump
The centrifugal pump moves liquids with the help of centrifugal force (this is why it is also known as a centrifugal pump). How it does this can be explained with a simple example: If you stir a glass of water quickly with a spoon, the water level in the middle of the glass drops while the level rises at the edge. This is where the centrifugal force works. The water at the edge is now higher than it was before when it was not moving. If you make a hole in the glass - at a point that the water reaches when it is in motion - then the water can flow off through the hole - it is transported.
In this example, the glass is the centrifugal pump and the water represents the liquid to be conveyed. The spoon is the impeller that is located in the pump and creates the flow.
The centrifugal pumps have a simple and robust structure. It consists of a housing, usually made of stainless steel, a drive shaft, the impeller and several inlet connections and drains. The impeller is arranged either axially, semi-axially or radially and moves at a high speed. Radial means that the pumped medium emerges from the impeller perpendicular to the pump shaft. With a closed impeller, the impeller blades are connected to a disk on both sides, which increases the hydraulic efficiency.
First, the water pump is vented, which is why a negative pressure is created in the centrifugal pump. This is the only way for the suction pipe to convey the liquid. Since the centrifugal force decreases the speed of the medium towards the outside, the pressure towards the outside also increases. The liquid is pressed by the pump wheel from the water pump into the outlets, for example into a concrete cistern, waste water collecting basin or rain barrels. Thanks to this property, even liquid-solid substances with different grain sizes can be conveyed. Speidel and Rewatec are manufacturers of special containers and tanks.
There are different types of centrifugal pumps:
- Axial pumps (also propeller pumps)
- Semi-axial pumps (also diagonal pumps)
- Side channel pumps
- Peripheral impeller pumps
- Radial pumps
- Special forms such as jet pumps and cell rinsing pumps
Centrifugal pumps, jet pumps & Co. work in different voltage ranges. They can cover everything from 12V (also continuous operation) to 230V voltage. The 230V jet pumps are particularly noticeable, as many in-house waterworks are equipped with pumps of this voltage. The reason: These are suitable for any power supply and also save electricity.
According to the VDMA (Association of German Mechanical and Plant Engineering) there are over 400 different types of pumps.
With centrifugal pumps there is a transfer of flow and kinetic energy between the liquid and the machine. That is why they are part of the flow and fluid energy machines. Of course, the delivery rate / delivery rate, the delivery head, the efficiency and the speed are also important and influencing factors for centrifugal pumps. A pump curve provides information about the relationship between pressure increase and flow rate.
Normal-priming and self-priming centrifugal pumps
The suction behavior is another property. Most centrifugal pumps are normal priming. This means that they are able to pump air out of the pressure chamber. This is important because if there is too much air in the pump, the pump will stop working. Even around eight percent air in the medium completely interrupts the flow. It is therefore particularly important that the centrifugal pump is vented. Only special self-priming centrifugal pumps, cell rinsing pumps and the jet pump are able to vent the suction line itself. Jet pumps are a subtype of centrifugal pumps and can even suck without filling the medium. That is the reason why jet pumps are also called self-priming. The side channel pump is also self-priming. This means that it can deliver pure gas as long as there is some residual liquid in the water pump. In addition, the part where the drive shaft enters the stainless steel pump housing must be carefully sealed.
Cavitation in centrifugal pumps
Cavitations should be avoided in centrifugal pumps as far as possible because they disrupt the flow of movement. Cavitation creates bubbles in the liquid that implode - the opposite of exploding: they collapse. This is of course not good for the flow in the pump and in the long run cavitations also affect the housing and the seals of the pump.
There are numerous different centrifugal pumps, such as the high-pressure centrifugal pump or the block centrifugal pump.
The different types can be distinguished according to:
- Pumped medium
- Shaft seal
- Alternating current or three-phase current
Differentiation according to housing
The housing of different centrifugal pumps differs particularly in the flow inlet and flow outlet. There are two forms of drainage of the pump:
- Diffuser with diffuser (= inverted nozzle)
- Spiral flow
Differentiation according to impeller
The impeller is the essential part of the centrifugal pump. The shape of the impeller creates the flow in the pump - and this differs depending on the shape of the impeller. There are three different forms:
- radial (pumped medium perpendicular to the pump shaft)
- axial (propeller pump)
If the pressure generated by a single impeller is insufficient, additional impellers are integrated into the pump (this is possible with radial and semi-axial pumps). This structure is called multi-stage pumps.
Differentiation according to shaft seal
The liquid in the pump must not escape at unforeseen places. That is why seals are important - also between the housing and the shaft. There are various options for shaft sealing:
- Stuffing box
- Labyrinth seal
- Radial shaft seal
- Mechanical seal
- Magnetic coupling
Differentiation according to drive
It often depends on the size of the pump which drive is used. An electric motor is sufficient for smaller models. Turbines are used in power plants where large pumps are required. The three-phase asynchronous motor is also available as a drive.
Differentiation according to material
Centrifugal pumps made of stainless steel and plastic centrifugal pumps can be chosen. Stainless steel centrifugal pumps are more hygienic than centrifugal pumps made of plastic.
Areas of application
The use of a centrifugal pump is versatile both in the house and garden, as well as in industry, which is why it is the most frequently used type of pump worldwide. Both single-stage and multi-stage pumps are used. In addition, the delivery head, also known as the suction head, can be between one and 5000 m. The suction lift is the usable work that is transferred from the pump to the pumped medium, based on the weight of the medium. The delivery rate depends largely on the funding amount. The centrifugal pump can convey both abrasive and pure media.
Below are some exemplary areas of application for the centrifugal pump:
- Domestic waterworks (rain collector): The domestic waterworks function is that it can bring about valuable tap water savings. The domestic waterworks replaces the tap water with groundwater and rainwater.
- Garden pumps / deep well pumps: With well pumps, the discharge pressure of the medium increases so enormously that it can also be pumped from great depths. The following applies to deep well pumps: the larger the garden pump, the more liquid can be moved even with low energy consumption.
- Plant and mechanical engineering, manufacturing technology
- Water supply in waterworks
- Water treatment and water disposal in swimming pools (swimming pool technology), collecting basins and pits
- Drainage from mines
- Fire brigade (fire fighting centrifugal pump)
- Oil production
- Chemical industry
- Food and beverage industry
- Process and environmental technology
- Dairy and beverage technology
- Wastewater technology (pure water and wastewater pumping)
- Ventilation of sewage treatment plants
Centrifugal pump manufacturer in the market
are EBARA, AGF, Schmalenberger, KSB, Zehnder, Schmitt, Radotech, Steinle, ORPU, ESPA (wholesale), megafixx, ALLWEILER, wilo, LEWA, ANDO
Every manufacturer of centrifugal pumps has pumps and systems of different series and delivery rates. These series are usually arranged according to specific requirements or additional equipment. In addition to the German manufacturers and service providers, pumps can also be purchased from companies all over the world. Examples are the Polish supplier Omnigena and the Portuguese manufacturer OLIJU.
Connect the centrifugal pump
The following things should be observed when connecting a centrifugal pump:
- The centrifugal pump has a delivery line and a suction line. Both should have the same connection size. The connection size is usually specified in inches
- The quality of the suction hose is also extremely important so that it can withstand the vacuum over the long term.
- The valve should be no more than seven meters above the minimum groundwater level.
- The foot valve, on the other hand, should be installed as high as possible. This prevents sand and other small parts that are pumped along with the pump from migrating upwards with the liquid.
Advantages of centrifugal pumps
Centrifugal pumps are the most widely used pumps in industry. No wonder they have some advantages:
- they have a high speed
- they have a long lifespan
- they are ideal for a high performance range
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