This is where we learn about how hydraulics work. We started off by ordering this universally handy pack of syringes off Amazon. Obviously, these get used for tons of other experiments and tasks as well, but in this case we wanted to leverage the various diameters to illustrate how force, pressure, and volume are effected by the change in diameter. To do this we drilled out a clear manifold in plastic, added a few tubing stubs and glued them in, then joined the assortment of syringes with a few random lengths of tygon tubing.

In order to really see the fluid flowing in this setup we did a few things to enhance that effect (if you just use one uniform liquid you can’t see any flow).

  1. We used the standard mix of colored water and mineral oil resulting in a pair of liquids inclined to stay separated.
  2. We added some fine iridescent glitter to the water mix so that there are some reflective particles in the fluid.
  3. We wired in a color changing LED concentric to the plunger on the largest syringe with a momentary switch on the pusher end. We sealed that LED into the rubber stopper with some glue. This continuously illuminates & animates the fluid within the large syringe.

Of course none of that is necessary- the setup will work the same way whether or not its decorated.

Some observations:

The friction in these syringes didn’t quite work the way I anticipated, I was thinking when you pressurize the large syringe they others would move in sequence, but they tend to get a bit more stuck than I expected.

Most of them have a rib around the end of the syringe that makes them inclined to stay installed. The smallest doesn’t because the diameter is so small I guess it would be hard to pull off.

It would be a good idea to tether these once they are installed. I’d do this by drilling a pair of holes in each syringe, one near the pusher end, and one in the body flange. Tie a string of some type between the two that equals the maximum length you’d like them to extend. That way you can avoid some of the accidental ejections we encoutered.

If these sit for a while, the stoppers will tend to swell a bit and so it will take some extra pressure to get them unstuck. It’s probably best if you empty them out after use so they’re not permanently in contact with the fluid- at least if you want to use these again for future experiments.

Of course these are all hydraulic actuators as well- so all of these can be used to create assorted mechanical actions- this is fun in some other activities as well.