Valves with piezo technology

Efficient open- and closed-loop control of gases in medical technology

Certain ceramics have piezoelectric properties, which means that when these ceramics are mechanically deformed, voltage is created in the material. This effect also occurs in the opposite direction: applying voltage to these ceramics leads to their deformation.

This piezoelectric behaviour can be used in many applications, for instance to generate or detect ultrasonic waves, as an ignition source (spark) for lighters or propane grills, or for precision movements of optical lenses for autofocus in smartphone cameras.

Piezo technology also offers a new way of developing valves to control the pressure or flow rate of gases. When voltage is applied to the piezo bender, it bends and lifts away from the valve seat. The higher the voltage, the more the actuator bends and the more the gas can flow through the valve.

Piezo ceramics act like a small capacitor, with the applied voltage charging the ceramic material and thus bending it. To regain its original shape, the material must be actively discharged. Piezoceramics do not require energy to maintain an existing mechanical deformation. Even after a power failure, the valve retains its current position.

Therefore energy is only required if the shape of the piezo bender has to be changed, i.e. the charge of the bender itself has to be changed. The amount of energy required in this case is very small (in the order of 1 mWs), as piezoceramics have a small capacitance (between 20 nF and 40 nF). Solenoid valves, on the other hand, require a continuous energy supply of several watts to maintain the open state, with the solenoid valve also heating up in the process.

Thanks to its low energy consumption, piezo technology is ideal for battery-powered devices (which consume much less power than solenoid valves) and for applications where the valves must not heat the gas.

Piezo technology has very specific advantages:

  • Proportional behaviour
  • No heat generation
  • Extremely low energy demand
  • Very compact and lightweight
  • Long service life
  • Intrinsic safety

Piezo valves cannot be used as a substitute for solenoid valves. Piezo valves operate at higher voltages of up to 310 V, while solenoid valves operate at 5, 12 or 24 V. Simple piezo driver electronics are always required to generate the necessary 250 – 310 V from the 5-, 12- or 24-volt power supply and to charge and discharge the piezo bender. Although 310V may seem high, the corresponding current is very low (max. 5 mA with 50 kOhm series resistor at the output). The piezo electronics can be designed to be electrically safe so that the voltage immediately drops to well below 50V when the contacts are touched.

Festo offers a wide range of valves with piezo technology for different flow rate or pressure requirements in a variety of applications. These valves can also be used to control pure oxygen gas, as their materials are tested for oxygen compatibility.

About the author

Thomas Kunert
Product Management MedLab

January 2018