I learned that steam locomotives used to have a reversing lever (a Johnson bar), whose position could be locked/unlocked and determined the steam pistons' cutoff. However, given enough steam pressure (e.g. during positive gradients), unlocking the lever might cause it to be thrown back into the operator, causing harm. They invented a more complex mechanism called a screw reverser to alleviate this.

I had a glass stopper stuck on a flask and started heating the flask to build pressure, then gave the stopper a firm, gloved twist. Air audibly rushed out and isopropanol violently bubbled for a few seconds. It was a cool demonstration of boiling point depression towards atmospheric pressure, but was annoying to deal with.