Difference Between Propeller and Impeller

Propeller vs Impeller

For those who have studied motion, especially that of different types of fans, there is no confusion between the terms propeller and impeller but ask those who think they have heard these two terms but haven’t studied them and you will get all sorts of answers. Part of the confusion is also because of similar sounding names but if one looks closely, the names themselves give away the meanings of the two different devices.

If you have ever seen pictures of ships closely, you must have noticed small rotating fans on both sides of the ship. These are propellers that actually help in propelling the ship forward. A propeller is an open running device that has the function of providing a thrust force. There is always a propelling fan on the mouth of an aircraft also. If we go by definitions given in various dictionaries, a propeller is a device having a revolving hub with rotating blades to propel an airplane, ship etc. In reality, a propeller is a special type of fan with blades that convert rotational motion into a force that helps in movement forward. This is because of a pressure difference that gets created between the front and the rear surfaces of the blades. This pressure difference pushes both air and water behind the blade. This thrust or force can be easily explained with the help of Newton’s laws of motion as well as Bernoulli’s theorem. Propellers are made heavy use of both in aviation as well as in ships.

Have you ever paid attention to the working behind the water pump that is used at home that sucks water from the main pipeline passing through the main road and brings it inside your home and then lifts it to the over head tank? The working principle behind this pump is the impeller inside a casing that creates a sucking force that draws in liquid at a great force and diverts it to your overhead tank. An impeller is always inside a casing as its purpose is to draw the liquid inside as against a propeller that provides an outward thrust and is always open. An impeller, because of its rotation and especially designed blades, increases the pressure of the fluid and thus its flow. A centrifugal pump used to draw fluid is the best example of an impeller.

In brief:

Propeller vs Impeller

• Both propeller and impeller are specially designed blades with a motor.

• While a propeller is designed to covert rotational motion into forward thrust, an impeller is designed to use rotational motion to suck fluid in.

• A propeller has an open design while an impeller is always inside a casing or housing.

  • danwat1234

    What about a submarine, that uses impellers then?

  • Ron Anderson

    A propeller moves itself, and whatever it is attached to, through a medium such as water or air whereas an impeller moves the medium (again, water or air) while itself remains stationary.

  • al_lajlaaj

    If you look out for the types of the pump blade u will find axial pump which acts exactly like a propeller
    i say if the fan or blade is used to move the body like ships and planes it is called propeller
    but if the body is stationary and moving another medium or object it is called impeller

    • Kenn Johnston

      Agreed; for example Turbine Agitators are not located in a housing, but are located in a tank or vault. They use impellers to cause the desired motion in the liquid within the vessel.

      • al_lajlaaj

        No actually it is not true.. after 9 months of my comment I learnt a lot.. it is not as I thought.. the propeller makes a difference in pressure before and after the blades thus driving the fluid and making the thrust therefore the ship moves. however the impeller adds a kinetic energy ( velocity) to the fluid and there has to be a change in the cross sectional area of the pipe (increase in diameter) and according to Bernoulli’s law that kinetic energy will convert to a pressure… now this comment i’m 100% sure