I am working on a project for college, and I am stuck on one idea that I don't really know how to represent it.

Basically what I want to do is something like a pipe, that if a put a kind of cylinder on inside from the top side, the cylinder will reach the end by force of gravity.

So something like this:

cylinder going down

But, if I turn the pipe, so I put the bottom on top and the top on the bottom, that cylinder must be stopped/blocked.

So something like this:

enter image description here

So my idea was to put some-kind of corrugated pipe as follows:

enter image description here

In this way the pipe will be one way only. As creating a pipe like this for a school project will be too hard, my questions is if is there already a pipe like this, if not if you have any other idea to achieve this.

  • 1
    $\begingroup$ It might be helpful if you tell us what you're trying to accomplish. Having a goal to work towards might generate better ideas than just giving us your take on a solution. $\endgroup$
    – grfrazee
    May 11, 2016 at 15:23
  • $\begingroup$ You could use the same principle as the floating hourglass. This works on a top heavy hourglass and friction between the walls, but I think that buoyancy also reduces the required friction. $\endgroup$
    – fibonatic
    May 11, 2016 at 18:23
  • $\begingroup$ What material does the pipe need to be? The plug? Can you share some sizes? (E.g. Is this a 1" pipe or a 20" pipe?) $\endgroup$
    – CBRF23
    May 11, 2016 at 18:39

2 Answers 2


Your idea would not be too hard to construct. The one direction tines can be installed through the side of the pipe. Any springy rod material could be used; plastic rod, spring steel, etc. Rubber would probably not be a good choice since it has higher friction and less restoring force than similarly sized plastic or spring steel.

Drill holes in the side of the pipe and insert the tines. Depending on the scale and wall thickness of the pipe you may need additional support to keep your tines at the angle without failure. This may require a gusset on each tine or a larger diameter pipe to anchor to.

A 45 degree angle and a passage slightly smaller than your object like you show would be a good starting point. You may have to change the geometry if you require changes in the passing or blocking forces.

Like mentioned in the comments, it is helpful if you can provide a bigger picture understanding of the design problem. There is often an easier solution that may not have been considered.


This is known as a "valve" (duh :-) ). If you have enough room in your pipe, cut a circular piece of similar pipe whose diameter is a bit less than the pipe's diameter. then mount this curved plate with a hinge on one side and mount a small stop on the other side. You want it set up so that when the pipe is in the "go" orientation, the plate falls down due to gravity and since it's curved, it goes flat against the pipe's interior. In the "stop" config, the plate falls against the stop and blocks the pipe.

Apologies for poor 3D rendering of the "potato chip" - shaped valve plate. Left picture is in blocking mode; right picture shows the tube with the other end up, in 'passthru' mode.

Tube up/down


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