Certain ceramics exhibit piezoelectric characteristics, meaning that when these ceramics are mechanically deformed, a voltage accumulates in the material. This effect also occurs in reverse: Applying a voltage to these ceramics will cause them to deform.
Piezo technology also provides a new way to design valves for controlling the pressure or flow of gases. If voltage is applied to the piezo bender, it will bend and lift off of a valve seat. The higher the voltage, the more the actuator bends and the more gas can flow through the valve.
Piezo technology has very specific advantages:
- Proportional behavior
- No heat generation
- Extremely low power requirements
- Very compact and lightweight
- Long service life
- Intrinsic safety
Piezo ceramics acts like a small capacitor in that the applied voltage actually charges the ceramic material, which in turn causes it to bend. In order to regain its original shape, the material must be actively discharged. No energy is needed in order for piezo ceramics to maintain an existing mechanical deformation. Even after a loss of power, the valve will maintain its current position.
This also means that energy is only needed when the shape of the piezo bender is to be changed, i.e., to change the charge on the bender itself. The amount of energy required in this case is very small (on the order of 1 mWs), since piezo ceramics have a small capacitance (in the range of 20 nF to 40 nF). By contrast, it takes several watts of continuously supplied energy for solenoid valves to maintain an open state—with the solenoid valve heating up in the process.
Its low energy consumption makes piezo technology ideal for battery-operated devices (which use much less power than solenoid valves) and for applications where valves cannot be allowed to heat the gas.
Piezo valves cannot be used as a drop-in replacement for solenoid valves. Piezo valves operate with higher voltages of up to 310V, whereas solenoid valves use 5, 12 or 24V. A simple set of piezo driver electronics is always required to generate the necessary 250 – 310V from the 5, 12 or 24V power supply, as well as to charge and discharge the piezo bender. Though 310V may seem high, the corresponding current is very small (max. 5 mA with 50 kOhm inline resistor at output). The piezo electronics can be designed to be electrically safe, so that the voltage instantly drops to well below 50V when the contacts are touched.
Festo offers a wide range of valves with piezo technology, for various flow or pressure requirements in a number of different applications. These valves can also be used to control 100% oxygen gas, since their materials are tested for oxygen compatibility.
This piezoelectric behavior can be used in many applications, such as generating or sensing ultrasonic waves, as the ignition source (spark) for cigarette lighters or propane grills, or for fine movements of optical lenses for the auto-focus in smartphone cameras.
Fully automated production of piezo valves
About the author
Product Management LifeTech
Festo AG & Co. KG