Valve technology dramatically reduces energy consumption.

Festo has developed piezo valve technology for gas handling that simplifies the replacement of traditional solenoid valves, facilitates integration and can reduce energy consumption by as much as 95%.

Extremely low energy consumption, coupled with silent, no-heat operation, makes piezo valve technology particularly attractive for laboratory and medical device applications. Low noise is prized for bedside medical instruments and devices and is also desired in the laboratories where a lot of instruments may be deployed. However, it has not been possible to simply replace standard magnetic solenoid valves with piezo technology because they operate very differently (see box-out). For example, most of today's control solenoid valves are designed to operate at a voltage between 5 and 24V, whilst a piezo valve requires 310V and special control electronics.

The benefits of piezo technology
The principle of piezo technology is quite different from that of a traditional, wound coil solenoid valve. The core element is the piezo ceramic bender. When this is electrically charged, it creates a polarisation within the crystalline structure that causes the ceramic material to bend. The bending is proportional to the applied voltage. By mounting the bender over a nozzle it enables the flow rate or pressure to be regulated proportionally. The higher the voltage, the greater the bender distortion and flow rate.

Solenoid valve coils require the electric power to be applied for the coil to remain actuated, whereas a piezo valve behaves like a capacitor. It only requires an initial current to energise the ceramic element and then the current consumption practically drops to zero, yet the ceramic bender will retain its shape until it is discharged or further energised.

In a piezo valve there can be one or two ceramic benders – and above each of these is a spring, which provides the return action. A single 2/2-way valve is a very easy way of controlling a flow rate. It has one bender and two ports. The higher the applied voltage, the further it opens. A 3/3-way valve function has three ports and utilises two benders. A complete pressure regulation system can be set up with this compact solution. It uses one bender for pressurisation (or increasing the pressure) and the second one for exhausting (or reducing the pressure). A third state to maintain the pressure is achieved by closing both benders, blocking the flow and pressure.

To overcome this potential barrier to adoption, Festo has developed piezo technology that enables piezo valves to be easily integrated into systems architectures using a standard 12 to 24V supply. Historically, consistent manufacture of piezo valves has been difficult. They assure reliability by producing piezo cartridges that can be incorporated into the various components on fully automated, high output production machinery. The cartridges consist of the fragile ceramic bender mounted within a housing incorporating the injection-moulded port nozzles. The gas flows in or out through these nozzles.

Their VAVE-P piezo valve incorporates everything needed for easy actuation. The VAVE-P is operated as normal with 12 to 24V and generates the required piezo voltage internally. It includes simple, open-loop actuation electronics, 310V voltage generation and a 2-channel piezo driver stage with current limitation. The two-channel electronics in the VAVE-P makes it possible to actuate two valves for regulating the flow rate passing through the valve or a 3/3-way valve function for regulating the pressure, using separate piezo valves for pressurisation and exhausting. This 3/3 way option is a very easy way of controlling pressure and is unique to piezo technology. The interface for the VAVE-P is always the same: two analogue inputs and the flexible power supply of 12 to 24V. There is no easier way to replace a proportional solenoid valve.

Using their piezo technology, it is easy to set up a complete flow rate and pressure regulation system. Another example is the compact VEMD flow control valve combining a piezo valve, flow sensor and control electronics. This allows you to achieve a linear ratio between input voltage and output flow rate. Its counterpart for regulating pressure is the VEAB proportional pressure regulator. This is equipped with two piezo valves, again each with one piezo bender for pressurisation and one for exhausting, plus the necessary electronics and a pressure sensor. The VEAB therefore provides a complete closed-loop pressure control solution in the smallest installation space.

The ability to purchase piezo valves as standard off-the-shelf components which are simple to integrate is opening up applications and uptake within laboratory instruments and medical devices applications. For specialist applications, Festo provides an application engineering and design support service.

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