Axial Flow Pump

In an axial flow pump, pressure is developed by flow of liquid over blades of airfoil section.

It consists of a propeller-type of impeller running in a casing. As the name suggests, in Axial

flow pumps the fluid enters and exits along the same direction parallel to the rotating shaft.

The advantage of an axial flow pump is its compact construction as well as its ability to run

at extremely high speeds. The flow area is the same at inlet and outlet and operates at

much lower pressures and higher flow rates.

Here we briefly discuss the general features, performance and utilization in Bangladesh of a

an axial flow pump

General Features:

Axial Flow Pumps or Propeller Pumps allow fluid to enter the impeller axially. They discharge

fluid nearly axially, pumping the liquid in a direction that is parallel to the pump shaft. An

axial flow pump is also called a propeller pump because the impeller works much like the

propeller of a boat. The propeller is driven by a motor that is either sealed directly in the

pump body or by a drive shaft that enters the pump tube from the side.

Axial flow pumps use the propelling action of the impeller vanes on the liquid to develop

pressure. Axial flow pumps can be adjusted by changing the pitch of the blades on the

propeller. This makes them useful for either high-flow/low-pressure applications or low-

flow/high-pressure applications.

Fig: A vertical axial flow pump Fig: A horizontal axis Axial Flow Pump

Construction:

An axial flow essentially consists of a propeller in a pipe. The propeller can be driven directly by a sealed motor in the pipe or mounted to the pipe from the outside or by a right-angle drive shaft that pierces the pipe.

Below a basic construction of a axial flow pump is shown

No Description

1 Coupling Key

2 Thrust Bearing Retainer

3 Thrust Bearing Retainer O-ring

4 Outboard Bearing

5 Spacer

6 Shaft

7 Bearing Housing

8 Filler Plug

9 Inboard Bearing

10 Laby Seal Inboard

11 Stuffing Box Cover O-ring

12 Mechanical Seal

13 Elbow

14 Impeller Key

15 Impeller 16 Impeller Lockplate

17 Impeller Screw

18 Stuffing Box Cover

19 Drip Pan

20 Sensor Plugs

21 Laby Seal Outboard

Performance:

Axial Flow Pump is the opposite of a Kaplan turbine. So they behave similarly and their

characteristics curves are almost similar. Some characteristics curves are given below –

Fig: Axial Flow Pump (Courtesy of Goulds Pump)

Fig: Performance curve of an axial flow pump

As seen from the curves the efficiency increases with increase of percent design flow and

the head decreases. For a typical axial flow pump, the head and brake horsepower both

increase drastically near shutoff as shown in Figure.

Uses:

Axial flow pumps are frequently used in industrial settings as circulation pumps that work in

conjunction with sewage digesters or evaporators. Axial flow pumps are also used in heat

recovery systems, nuclear reactor water circulation, and high volume mixing applications.

Axial flow pumps can also be used as a liquid pump for ballast control in marine

applications.

Axial flow pumps use the propeller action to draw water into the pump by suction. An axial

flow pump can be designed as a suction pump that draws water in through one end and

discharges it out the top of the pump. However, axial flow pumps are not typically used for

suction lift applications.

Axial flow pumps used for pumping clear water or storm water may also be submersible. A

submersible pump that uses an axial flow design is common in irrigation and drainage

applications. Axial flow pumps may also be used as a sump pump in some industrial

applications to circulate slurries or wastewater or to drain storm water from sump pits or

waste storage lagoons. Axial flow pumps are typically used in high flow rate, low lift

applications. A mixed flow pump similar to a turbine pump may be used as a well pump

provided the well is not too deep.

Utilization in Bangladesh:

The main advantage of an Axial Flow Pump is that it can easily be adjusted to run at peak

efficiency at low-flow/high-pressure and high-flow/low-pressure by changing the pitch on

the propeller (some models only). These pumps have the smallest of the dimensions among

many of the conventional pumps and are more suited for low heads and higher discharges.

Considering this features it can be utilized in Bangladesh at various sectors like –

Chemical - evaporator and crystallizer circulation

Mining and Minerals - phosphate, soda ash, potash and sodium chloride processing

Petrochemical - polypropylene reactors, xylene

Pulp & Paper - black liquor evaporator, chlorine dioxide generators

Municipal - sewage digesters

General - Raw water pumping, flood control, marine ballast transfer