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Saturday, 14 September 2019

AXIAL FLOW PUMP WORKING PRINCIPLE

We were discussing the pumps and basic pumping systemtotal head developed by the centrifugal pumpparts of centrifugal pump and their functionheads and efficiencies of a centrifugal pumpwork done by the centrifugal pump on waterexpression for minimum starting speed of a centrifugal pumpmultistage centrifugal pumpscavitation in hydraulic machinespecific speed of a centrifugal pumpcavitation in hydraulic turbinescavitation in centrifugal pumps, maximum suction lift of centrifugal pump and net positive suction head of centrifugal pump  in our previous post.

Today, we will find out here a new topic i.e. axial flow pump working principle with the help of this post. We will find out here the basics behind the axial flow pump, components of axial flow pump and further we will see the working principle of axial flow pump. 

Axial flow pump working principle 

Axial flow pump could be defined as a pump where liquid i.e. water will flow in axial direction. Here we have used one term i.e. axial direction. Axial direction means liquid will flow in the direction of axis of rotation. 

In case of axial flow pump, inlet and outlet of fluid will not vary in radial location from its axis of rotation. 

Axial flow pump could be considered as the converse of an axial flow reaction turbine.
Axial flow pumps will be used when we need to deliver the higher flow rate and relatively lower head. 

Axial flow pump: Components and their function 

Following figure shows here the basic schematic view of an axial flow pump. 


There will be a central hub in an axial flow pump as shown in figure and a number of vanes or blades will be mounted over this central hub of axial flow pump. Therefore, the central hub with a number of vanes or blades will be called as the rotor or impeller of the axial flow pump. 

Impeller blades will be mounted over the central hub of axial flow pump in such a way that liquid i.e. water may flow axially through these impeller blades. 

Impeller will be rotated within a cylindrical housing as displayed in above figure. There will be a clearance between impeller and cylindrical housing and this clearance should be as less as possible in order to avoid the leakage. 

Now we will see here the stationary inlet guide vanes of an axial flow pump as shown in above figure. These stationary guide vanes are provided at inlet of an axial flow pump in order to direct the liquid i.e. water in correct way to the impeller blades without any shock. 

There will also be some stationary outlet guide vanes at the outlet of an axial flow pump as shown in above figure. Stationary outlet guide vanes are basically provided at the outlet of an axial flow pump in order to change the direction of motion of liquid coming from the outlet of impeller. 

When liquid will come from the impeller outlet, it will have whirling component of velocity along with the axial component of velocity. Stationary outlet guide vanes will reduce this whirling component of velocity. After passing through the stationary outlet guide vanes, liquid will flow almost in axial direction i.e. in a direction parallel to the axis of rotation. 

We must note it here that the number of impeller blades will vary from 2 to 8 in an axial flow pump.
Ratio of hub diameter to the rotor diameter for an axial flow pump will be in the range of 0.3 to 0.6. 

Therefore, we have seen here the basics of axial flow pump. We have also discussed here the various important components of axial flow pump and their function too with the help of this post. 

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Further we will find out, in our next post. 

Reference: 

Fluid mechanics, By R. K. Bansal 
Fluid Machines, By Prof. S. K. Som

Image courtesy: Google 

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