Today, I'm going to describe the fourth puzzle from Roscreative, the Rudenko Doser, designed by Valery Rudenko (English). Check out the three previous reviews here, here and here. Only one left...

The Rudenko Doser is unlike any other puzzle you've seen. This very original design reminiscent of an hourglass is based on the task of mathematician Siméon Poisson for measuring liquids. There are three vessels: the main one is connected to the two smaller vessels with taps to open and close the flow of "liquid" (represented by a green sand-like material). The puzzle is double-sided, as the smaller vessels are marked with capacities of 5 and 3 liters on one side and 7 and 5 liters on the other. There's also a tap between the smaller vessels to pour "liquid" from one to another.

(Click to Enlarge) - Hard Side

As mentioned above, there are multiple tasks for you to try and solve, more specifically, three on each side: On the easy side, with marks for 5 and 3 liters, you have to successfully measure 2, 1, and 4 liters; On the hard side, with the 7 and 5 liters, you need to correctly measure 3, 4, and 1 liters. These number sequences are in order from easier to harder. Also, note that the marks are just representations of the actual measurements, as the puzzle is relatively small, at about 9 x 9cm (3.5").

Solving the puzzle's challenges is not that difficult, even the ones on the harder side. Most of the tasks require multiple dosages in each vessel to get to the desired measurement, so the hard part might be to plan in advance how you will distribute the "liquid" back and forth. As an example, I'll describe below one of the easier tasks for you to get an idea on how to solve them, but the other ones follow the same exact logic, only lengthier.

(Click to Enlarge) - Both Vessels Full

So, one of the challenges is to accurately measure 2 liters with the 5 and 3 liter vessels. The first step is to completely fill the 5 liter vessel. When you're done, rotate the puzzle counter-clockwise by 90º and open the green tap, the one between the two smaller vessels. This action will allow you to fill the 3 liter vessel, leaving the rest of the "liquid" in the 5 liter one. What you see left in the 5 liter container is the exact measure of 2 liters. The other challenges won't be that simple, though, but still solvable within 5 minutes each. It took me less than half an hour to solve all six tasks.

Video: To have a better idea of how the puzzle works, check out this video with Mr. Rudenko.

Closing Comments:

If you loved mathematics related tasks or computer science projects in school, then you're certainly going to enjoy the Rudenko Doser. What I liked most about it was the hourglass appearance - It's definitely quite a unique design. Be careful when maneuvering the puzzle, though, as it tends to shed some of its green sand particles here and there. Nevertheless, it's a great looking puzzle and I can surely recommend it to any puzzle enthusiast.

Availability: You can buy Rudenko puzzles at Hendrik Haak's Puzzle Shop, from Germany or Labirint.ru in Russia (English translation here). For wholesale, contact Roscreative directly.

Now available on PuzzleMaster as well.

Links: 

English translation of Rudenko Doser's page

English translation of Roscreative website

Russian Magazine Article about Valery Rudenko (English Translation)

Russian Newspaper Article about Valery Rudenko (English Translation)