The 6 Slider Puzzle

This is a puzzle for a valve or something similar; perhaps it drains or fills a pool, and it’s important that it not be easy to trip accidentally. The heroes find a valve next to two slider rails with three sliders each.

They learned from a sage, fellow adventurer, or book that the way to open (or close) the valve is to move the nickel sliders from left to right and the brass sliders from right to left. But they may or may not learn (until they try it) that they can only move one at a time and only in one direction.

The nickel sliders move only to the right. The brass sliders move only to the left. Each slider can only move into the empty space. A nickel slider and a brass slider cannot occupy the same position. A slider can move past a slider of the opposite color but, of course, not those of the same color.

Example of a valid position after two moves.

Example of an invalid position. Sliders cannot occupy the same vertical position.

If you get stuck, you can pull the large lever to reset all the sliders. It returns to the up position and can be used again. This incurs a minor wild magic effect (or a painful shock or some other minor punishment) on the character using it.

Use different coins or checkers to simulate the different colored sliders and let the players play with it, resetting it as necessary.

Solution

There are any number of ways to solve the puzzle, but the key is to avoid moving a slider next to another of the same color unless it is to reach its final position.

Brass A moves (1), then nickel A moves past it (2).

Nickel B moves (3), then brass A slides past it (4), followed by brass B sliding past nickel A (5).

Brass C moves (6), then nickel A slides past it home (7). Next, nickel B can slide past brass B (8).
After that, nickel C will slide past brass A so brass A can slide home.
Continue until all sliders are moved home.

Variations

For added danger, you might say that, on a 1 in 4, the large lever breaks off after a reset (stopping them from resetting again or, if you like, forcing them to do some ad hoc repair).

If you prefer a simpler solution, just say that the sliders can move backwards as well as forwards. That avoids getting stuck and having to reset, so there’s no need for the reset lever.