The principle of piezo technology cannot be compared with a solenoid valve. The core element is the piezo ceramics. When this is electrically charged, it creates a polarisation that causes the ceramic material to bend. The bending is proportional to the applied voltage and enables the flow rate or pressure to be regulated proportionally. The higher the voltage, the greater the flow rate. The current consumption curve is completely different than for a proportional solenoid valve, whose coil is permanently energised. This is the only way to generate the magnetic field that lifts the armature away from the valve seat. A piezo valve, on the other hand, does not need to be constantly energised, since it behaves like a capacitor. To charge the ceramic material once, all you need is an initial current and then the current consumption practically drops to zero.
The design of piezo valves is very simple. They consist of a housing with ports, with the nozzles injection moulded into it. The gas flows in or out through these nozzles. There are one or two benders – made from the ceramic material – and above each of them a spring, which provides the return action.
A 2/2-way valve is a very easy way of controlling a flow rate. It has one bender and two ports. The more voltage is applied, the further it opens.
A 3/3-way valve has three ports and two benders. A complete pressure regulation system can be set up with this compact solution. There is one bender for pressurisation (or increasing the pressure) and a second one for exhausting (or reducing the pressure). The third state is closed; this is when the pressure is maintained. A 3/3-way valve like this is a very easy way of controlling pressure. Solenoid valves do not have a 3/3-way function like this.
As mentioned earlier, piezo valves do not operate using 12 V – they need special electronics. To make actuation much easier, Festo has developed piezo driver electronics in the shape of the new solution VAVE-P that has everything needed for piezo technology.
The VAVE-P is operated as normal with 12 to 24 V and generates the piezo voltage. It has everything you need for the specific actuation of piezo valves: simple open-loop actuation electronics, 310 V voltage generation and the 2-channel piezo driver stage with current limitation.
The two-channel electronics makes it possible to actuate two valves for regulating the flow rate or a 3/3-way valve for regulating the pressure with separate actuation for pressurisation and exhausting.
The interface is always the same, two analogue inputs and the flexible power supply of 12 to 24 volts. There is no easier way to replace a proportional solenoid valve.
There are also solutions that come with all the components required for a complete flow rate or pressure regulation system. The compact flow control valve VEMD from Festo combines a piezo valve, flow sensor and control electronics. This allows you to achieve an absolutely linear ratio of input voltage and output flow rate.
The counterpart for regulating pressure is the proportional pressure control valve VEAB with two piezo valves, in each case with one piezo bender for pressurisation and one for exhausting. Then there is also the electronics and a pressure sensor. This provides a complete closed-loop pressure control solution in the smallest installation space.