Mindstorms Vacuum Pump
The LEGO pneumatics system is meant to compress air, but I wondered if I could use it to pull a vacuum. After much experimentation, I found that I could build a vacuum pump. This vacuum pump is based on pneumatic cylinders being pulled, which creates a momentary suction. The problem is that when the cylinder is reset, compression occurs that cancels out the negative pressure. But by placing a valve in line with the cylinder, the compression stroke can be canceled out. All this is diagramed in the sketch below—two cylinders are involved, one connected to each top port of a pneumatic valve. The valve is motorized to alternate directions as the cylinders alternate between compression/suction. The video below shows everything working together.
Use of the vacuum pump is in the video below, using an Erlenmeyer flask as a vacuum chamber. The vacuum pump pulls air out of the flask. With a tube connecting the flask to a liquid, the liquid gets sucked into the flask.
The next question to investigate was how good of a vacuum pump is this. Well, it’s not very good. I used the Dexter Industries dPressure sensor (see my other blog post on LEGO Regulated Air Compressor) to find that the strongest vacuum I can pull is only 55 kPa below ambient barometric pressure. The limiting factor in the design seems to be the pneumatic valve, which leaks a little every time the valve is switched. But in defense the valve, it’s not meant to work in a vacuum system. I’m using the valve for something it was not designed for.