A air pressure regulator switch make it able to stop a compressor when a certain pressure piek level is reached or start a compressor when a certain low level is reached. A LEGO pole reverser will switch the electric power off and on when it is moved by the piston of a small cylinder. The piston is pulled back by two rubber bands, but when the pressure rise the piston pushes the pole reverser around. This fundamental idea is used by The Hempel design group, Jennifer Clark and many others to regulate the pressure for their pneumatic LEGO designs.
When you press the piston of the large cylinder the pressure in the tube will rise. This will push the piston of the small cylinder which will then turn the pole reverser. At a certain pressure level the pole reverser will switch of and the light will go out. At what level of pressure the pole reverser will switch depends on the elastic bands. I my case it switches off at about 1950 mBar (28.28 PSI).
Releasing air by stop pressing the large piston will switch on the pole reverser again. I my case it switch on at about 920 mBar (13.34PSI). You can influance this by adjusting the tension of the rubber band. I used the NXT Mindsensors pressure sensor to measure this.
note: PSI means pounds per square inch.
1 Bar = 100 kPa (kilopascals) = 1,000,000 dynes per square centimeter (baryes)
1 Bar (1000 mBar) = 14.5038 PSI
1 PSI = 0.068947mBar
(for more info look at http://www.convertworld.com/en/pressure)
A video of an "old style" LEGO pneumatic pressure regulator based on an electric pole reverser, polarity switch part no: 6551:
The new pole reverser acts like the old one, but there are some small differences:
- It can't turn continuness. It turns only a fourth part of a turn.
- I is only 5 studes long (one stude less then the old pole reverser).
- It needs a bit more force to turn it.
To overcome this last problem I used longer lift arms in my design of the new style pneumatic LEGO pressure regulator switch.
A video of a new style LEGO pneumatic pressure regulator based on a Electric, Pole Reverser / Polarity Switch with Black Lead, Power Functions bb339c01: