An actuator, which closes a valve needle, is chosen for spring type loads. The selected load curve has section wise different stiffness. In the first phase, the needle moves freely. Then, the needle gets into contact with the seat and forces increases steeper when compressing the surface roughness. In the third phase, the needle is pressed increasingly into the seat and closes the valve.
In the next figure a displacement-force diagram of a selected piezo stack is shown, where different states of the actuator (-30V, +20V, 100V and 150 V) are indicated. Forces are in compressive direction. Each line represents the elastic mechanical behaviour of a piezo at a constant voltage condition.
When the voltage applied across the piezo terminals increases, the needle moves. At 20V the needle reaches the seat and compress the material in the surface roughness region. At 100V the needle is completely driven into the seat and further voltage increase compresses the valve seat. The chosen actuator is a 5x5x20mm Piezotechnik stack. The valve force reaches 350 N, which fit with a high-pressure valve. Such a design is preferable for strong and precise acting fast valve.