help explain how a plumbing snake works in terms of physics

March 29, 2016 7:53 AM

Spouse has been using an electric eel for the past few days and is curious about the physics of how the snake travels through the pipe. He doesn't understand how the machine pushes the snake in to the pipe or how the snake travels through the pipe. We are having a hard time finding good search terms for this. It's easy to find information on how to use a machine auger, but not easy to know what to look up to understand the physics behind it. Does it have to do with springs? How things coil?
posted by bleary to Science & Nature (6 answers total)

I can't find any good diagrams or animations either. It has to do with how a helix works. Imagine an S wiggling through the drain - it brushes against the walls of the drain, pushing the entire time, so it's scraping something off the inner surface of the drain and it's pushing against/through something in the middle of the drain, and it's turning the entire time, and between those three motions it dislodges, loosens, scrapes, tunnels, and churns, plus there's the considerable pushing force it can exert by the nature of the narrow space and the strength of an articulated snake.

If you have a length of wire or a twist-tie from a loaf of bread or some packaging, try to straighten it as much as you can and then look at it side-on as you turn it in your fingers. Even the tiniest crimp will bow outward, and if you push the other end against a surface or your hand, you'll see how the pressure makes the whole thing bow out even more. If you do it inside a narrow drinking glass or bottle, you'll see how it makes contact with the walls.

The machine is cranking the snake out and turning it, same way a hand auger would. It doesn't take a very large orbit at the source to translate into a lot of helixing power down the line of the snake.

You can actually sort of see the motion here, just as he says "homeowner version of a drain snake" and cranks the handle. You can see it again at 1:13.
posted by Lyn Never at 8:40 AM on March 29, 2016

Picture how you would drive a screw into a piece of wood, then pull up on the screw. The wood comes up as well, right?

You're using the tip of the snake to spin into (or past) the block, then pushing/pulling with the stiffer part of the cable to draw the blockage out.
posted by JoeZydeco at 9:04 AM on March 29, 2016

Response by poster: To clarify, we are wondering what causes the snake to be propelled through the pipe, not for how the material is pulled out.

The machine applies a force in a direction perpendicular to the pipe, and the snake is propelled through the pipe instead of buckling outside the pipe. I think one reason it doesn't happen is that it is a short distance away from the opening and that the snake is too rigid to buckle out versus traveling along the pipe. But really, I don't know all this or the mechanics of it.

I thought of more search terms. I know this is not literally a snake, but snakes propel themselves with sideways motion, so I looked up biomechanics of snake motion and found a lab that links to a video they made of a snake in a clear tunnel. https://www.youtube.com/watch?v=E-U986N-9EI you can see it bunch up, and then when it stretches out that pushes it along the tunnel. I don't know how similar that is, but it may be.
posted by bleary at 9:15 AM on March 29, 2016

It sounds like a screw. You turn the screw sideways, but it goes inward because it is restricted by the wood. You crank the snake sideways, but it goes forward because it is restricted (probably by the machine).

I've heard the screw described as an example of the "basic machine" the inclined plane (it redirects force), and that might be a helpful way to think about it.
posted by Lady Li at 9:41 AM on March 29, 2016

It will buckle outside the pipe if there's an immovable blockage very close to the opening. But once you're far enough in to complete a wave inside the pipe, it won't unless the tip snags so it can't turn and the whole thing twists up.
posted by Lyn Never at 9:45 AM on March 29, 2016

It's not an elegant thing, a drain snake. An electric one (looks like a drill with an drum on the front) has an automatic feeder. The snake itself is fairly rigid, coiled wire that will, reluctantly, bend but will then readily bend back again.
Most importantly, resting on the bottom of a pipe, it wants to go forward due to its rigidity. If it encounters a blockage the end of the snake has a grabber/digger to help get through it. Again, think rigid flexibility due to the coil. Digs into the blockage and then pushes through.
posted by From Bklyn at 9:53 PM on March 29, 2016