The very clever way Clupet piston rings are made

May 16, 2023

I was unwittingly amazed yesterday when I came across a video about how Clupet piston rings are made (and learned the word ‘Clupet’ at the same time).

Unlike a car piston ring which is a single ring with a small gap, a Clupet ring has two turns (see photo from the Peter’s Railway YouTube video, linked below) with no gap between the two loops.

In fact, the loops press against each other.

How to make such a thing?

It turns out that the double ring starts life with a gap, carefully sawn from a tube – so the gap is as wide as the saw blade.

The cunning part is, that they are then turned inside-out.

Well, I say ‘inside-out’, but I don’t know the exact phrase for what really happens – one ring tip is fiddled pulled over the other ring, and the process continued until the two rings have swapped place.

This is all the more amazing as the material is cast iron, a stiff brittle material prone to snapping.

The inside-out double-ring is then stretched to have a big gap, and then heat-treated to make that big gap permanent.

Now the double ring is once more carefully turned inside-out, turning what would have been a permanent big gap into spring force which firmly holds the two rings together.

Is that not amazing?

As an added advantage, all sides of both rings are accessable at one time or another during this process, allowing all surfaces to be tided up easily.

Hats off to Peter’s Railway for making one in front of us: How to Make Clupet Piston Rings at Peter’s Railway

Update: in trying to find out who Mr or Ms Clupet was (the word always seems to be written with a capital ‘C’), I discoverd that, According to the Science Museum, at least one type of Clupet piston rings was patented by Clews and Peterson in 1919.….mental gears turn… ah ha: the initial letters of the names and a spurious ‘u’ – maybe Clepet was already taken 🙂

If the image above has been used inappropriately, please get in touch so that I can remove it.