What is a Mixed flow Pump?

mixed flow pump
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The mixed flow pump is a famous kind of centrifugal pump that combines an axial flow pump and a radial pump. It works by the combined action of centrifugal force and thrust due to the impeller rotation, and the direction of the liquid coming out of the impeller is inclined on the axis. 

These types of pumps are turbines that use the centrifugal force generated by a rotating impeller to pump a liquid. The rotating impeller of the pump accelerates the liquid under the effect of centrifugal force.

As the velocity of the pump rises, the dynamic pressure of the fluid also increases. When it exits the impeller, the accumulation of liquid causes the liquid to slow down again at the outlet. Therefore, the dynamic pressure of a liquid is converted into static pressure (for more information on the relationship between dynamic pressure and static pressure, see the article on the Venturi effect). 

As a result, the static pressure at the outlet opening has increased significantly. This high pressure enables the liquid to exceed certain geodetic heights. Increasing the speed increases the dynamic pressure of the fluid. When it exits the impeller, the accumulation of liquid causes the liquid to slow down again at the outlet. Therefore, the dynamic pressure of a liquid is converted into static pressure (for more information on the relationship between dynamic pressure and static pressure, see the article on the Venturi effect). As a result, the static pressure at the outlet opening has increased significantly. This high pressure enables the liquid to exceed certain geodetic heights. 

Working of Mixed flow Pump

When the prime mover turns the impeller, follow the principle of operation. In the working of the mixed flow pump, both the axial and radial thrust act on the fluid.  This means that it is a combination of the radial-pump and the axial flow pump. A mixed flow pump is faster than radial pumps, slower than axial pumps. The delivery head is higher than with the axial flow pump but lower than with the radial pump, and the delivery flow is smaller than with the axial flow pump and greater than with the radial pump. 

Mixed flow pumps are mainly used for agricultural irrigation and septic tank pumping, rural drainage, and as water circulation pumps for thermal power plants.

Design of Mixed Flow Pump

The mixed flow pump is a “pull” structure pump that checks and removes the impeller and shaft seal, separates them from the pump body, and does not connect them to the pipeline. The pump shaft is precision machined with oil-lubricated thin bearings, and the shaft has a sleeve with a stuffing box cover. Bearing housings containing oil can control a certain fill level of the oil injection nozzles.

The legs of the pump body withstand any load from the pipeline and transfer it directly to the base. This way, the rotor cannot bear the bending load of the pump, which maximizes bearing life.

The high area of the flow reduces obstacles. The orientation of the of the pump’s turning is clockwise, as seen from the side of the driver’s seat. An electrically powered motor or an IC engine. The pumping unit may equip with a complete ventilation system that facilitates evacuation of the suction tube. 

What is Cavitation? 

The negative pressure generated at the suction connection causes the pump to suck in liquid. More precisely, a high ambient pressure outside the suction line pushes the liquid towards the pump in the direction of negative pressure (principle of drinking through a straw). At an ambient pressure of 1 bar, the pump can generate a maximum vacuum. The pressure with which the liquid can be pumped into the pump is therefore limited to a maximum of 1 bar. This makes it possible to obtain only a limited number of geodetic chips. When pumping, the maximum suction height when creating a full vacuum is theoretically 10 meters. 

The ambient pressure and cavitation limit the suction lift of the mixed flow pump. Cavitation is the formation of vapor bubbles when the static pressure of a liquid is less than the vapor pressure. The vapor pressure of water at a temperature of 20 ° C is 23 bar. If the static pressure in the water is below this value. In that case, the water starts to evaporate locally, even at such low temperatures, forming small bubbles (similar to the steam bubbles that rise when water is boiled). 

When the pressure inside the pump rises again, the bubbles become unstable and implode. Since it is a bubble, the particle density is relatively low. Therefore, the bubbles burst with little resistance. The surrounding liquid is accelerated in the collapsed bubbles to such an extent that the resulting microjet generates a local pressure of thousands of atmospheres. When this microjet hits the impeller blade, it will cause damage over time. Cavitation is generally recognized by loud noises and pump vibrations. 

Applications of Mixed flow Pumps

  1. They use for pumping the septic tank
  2. These types of pumps are used in agricultural irrigation. 
  3. These also use for water level controllers at the dam. 
  4. They use to provide safety from heavy rain and assists to control floods. 
  5. They also utilize to control the cool water circulation at power plants. 
  6. A mixed flow pump also uses for pumping seawater. 

 

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