The pressure compensation vessel (PCV) just helps control the liquid level in the pipettes. It has an electrocaloric liquid level sensor that is used as a closed feedback loop for controlling the liquid level in the bottle. So the bottle has inside a heater and heat sensor that is positioned in a waterproof container. There is an Arduino microcontroller that is used for controlling the feedback. More details about how it works is posted here.

The system includes:

1. 500ml bottle with modified hood for connecting liquid input, output, electrocaloric sensor and air stone filter
2. Tubing
3. Bottle clamp for mounting
4. Waterproof electrocaloric sensor
5. Optional: peristalic pump
6. Optional: control electronics, command line software and power supply