Engineering360: "Impeller vs. propeller: What's the difference?"

What about when you put the boat in reverse?

It would seem that the inlet side of a propeller would be an impeller - you have to draw the water in to push it away.

So the only difference is which way you happen to be facing at the time....seems rather arbitrary....

It's not my field, but my understanding is that an impeller pulls on the water whereas a propeller pushes it. Pushing water away requires that new water is pulled in to replace it. So you can have impellers alone, but a propeller is also part impeller.

Is not an impeller also pushing water away? I don't see how you can have push and no pull or vice versa....the water is moving in one direction coming and going....now the 'impeller you picture is quite different in design as it slings water away by centrifugal force, I get that....but that's a pump type, correct?

I guess if it's part of a pump, it's an impeller, and if it pushes a boat it's a propeller. They both essentially do the same thing, move water, but maybe are design optimized for different jobs.

What about a jet drive boat?

Sucks water from the bottom and shoots it out the back...

A jet drive is just a shrouded propeller.

I say it's in the name. A propeller "propels" water in a single direction in order to generate thrust. An impeller moves water but not necessarily in a single direction.

I think that's right, an impeller needs to be in a housing, and a propeller doesn't....

I have one of those window fans that is reversible, it's converted to DC and you switch the polarity, but it does seem to move more air one way than the other....but not by much....

Berkeley Jets. Page 25, Item No 9, reverse bucket. I am sure you will figure it out from the part list what makes a Berkeley jet motor propel a craft backwards.

Not rocket science at all, simply reverse thrust.

https://www.cpperformance.com/Instructions/berkmanual.pdf

Strangest thing, it goes backwards.

Thrusters.

Are they impellers or propellers?

Seeing that the US Navy, heavy work tugboats and nearly every cruise ship use them an enquiring mind wants to know.

Seems they can be either...

..."There are three general types of thrust devices: the lateral thruster or tunnel thruster, which consists of a propeller installed in a athwartship tunnel; a jet thruster which consists of a pump taking suction from the keel and discharge to either side; and azimuthal thruster, which can be rotated through 360°."...

https://www.wartsila.com/encyclopedia/term/thrusters

This article is really quite a poor explanation, and much of it is just downright wrong. Some clarification, I hope:

• The Archimedes screw most certainly cannot be looked at as "a very early and basic version of an impeller"! It is a totally different principle, and it is a positive displacement pump. You could get away with calling a propeller a screw (as ships propellers used to be known), but not an impeller.
• It is wrong to say that the impeller "creates an intrinsic sucking force" whilst propellers 'push'. It is generally accepted these days that impellers don't 'suck', but rather the act of 'impelling' the fluid through the impeller to the discharge creates a lower pressure than exists in the suction system (usually a combination of suction head and atmospheric pressure), and fluid naturally flows from the higher pressure zone to the lower pressure zone. Most definitions of 'suction' will confirm this. So it is wrong to say that an impeller sucks whilst a propeller pushes.
• So the functions are in fact exactly the same, only the purposes are different. The function involves imparting energy from the motive drive via the impeller/propeller to the fluid in the form of flow and pressure. The amount and balance of flow and pressure required by the application determines the geometry of the impeller, so a typical process centrif usually means radial flow flow for low flow/high pressure, whilst something like a large irrigation pump might involve a very large flowrate with minimal head, meaning an axial flow pump/impeller is required. The axial flow impeller looks just like a propeller, and will always include an element of centrifugal/radial force, and all impellers/pumps from fully radial to fully axial obey the Affinity Laws (a.k.a. Pump Laws, Fan Laws, etc.) Most centrifs are usually mixed flow.
• 
• 
• But the purposes of impellers and propellers are completely different. The purpose of an impeller is to move a fluid from A to B, simple as that. Granted the propeller also moves fluid, but it's real purpose is to propel the craft it is attached to, whether it's a boat or an airplane, it's purpose is the same, to create THRUST. When you specify a pump you consider the flowrate and pressure required, but when you specify an aircraft engine there is no mention of flowrate or pressure, only thrust.
• As Rixter rightly said, a jet drive is just a shrouded propeller (as is a thruster).

My thought is

Most propellers move the fluid in an Axial direction using a screw action in the open. Impellers generally move it in a Radial direction using centrifugal action in a casing.

After reading the post and all the responses the only real difference seems to be

1. a casing
2. what your selling
3. and who you're selling it to

Tagging to Solar's response to my first comment; what's the difference well that depends were you are and how you parse on the continuum of thrust.