Anatomy of an impeller
Eye, vanes, shrouds, hub and shaft — name every part and what it is for.
⏱ 5 min
- Everyday comparisonStep 1 of 6
Like a bicycle wheel
A bicycle wheel has a hub in the middle, spokes going outward, and a rim holding it all together. Every part has a job.
An impeller is built the same way: a hub in the middle, vanes instead of spokes, and discs instead of a rim.
- Try itStep 2 of 6
Take it apart
Drag the Pull apart slider to open the impeller up. The labels show each part.
Turn on the see-through shroud to look inside the closed channels where the water flows.
Challenge: Pull it apart all the way, then spin it around. How many vanes does it have? Change the number with the Vanes slider.
- ExplainedStep 3 of 6
The parts, from the water’s point of view
Eye — the round opening where water enters. Vanes — the curved blades that push the water outward. The spaces between vanes are the water’s channels.
Front [[shroud]] — the disc that covers the vanes on the inlet side (it has the eye cut in it). Back shroud — the disc that carries the vanes. [[hub|Hub]] — the thick centre that grips the [[shaft|shaft]].
- ExplainedStep 4 of 6
The little ring that saves a lot
The water at the edge has high pressure; the water at the eye has low pressure. So some water tries to sneak back from the edge to the eye, around the outside of the front shroud.
To stop it, pumps keep that gap tiny — about the thickness of a few sheets of paper — with a . When it wears out, it is swapped for a new one instead of replacing the whole impeller.
- Try itStep 5 of 6
More vanes or fewer?
Most pump impellers have 5 to 7 vanes. More vanes guide the water better, but each one takes up room and adds friction.
Change the number of vanes and watch how the channels get narrower or wider.
Challenge: Try 2 vanes, then 10. Which one leaves the water less guided (drops wandering between vanes)?
- The impeller connectionStep 6 of 6
What they are made of
Clean-water impellers are often bronze, cast iron or stainless steel. Cheap small pumps use plastic. Pumps for sand or mud use hard chrome iron or even rubber, which bounces grit off.
The material is chosen for what the liquid does to it: sea water corrodes, sand scratches, acids eat metal.
📌 Remember this
Water enters at the eye, is pushed by the vanes through channels between the shrouds, and leaves at the edge. The hub holds it all on the shaft, and a wear ring stops water leaking back.