Because a piezo element behaves electrically as a capacitor rather than as a coil. Charging it takes a brief current; holding the charge takes practically none. A solenoid, by contrast, has to keep current flowing through its winding for as long as it is energised, and that current is what becomes heat.

Because a warm valve warms the gas passing through it and the structure around it, and in analytical, medical and metrology equipment that shift is large enough to move the reading. A manifold of solenoids inside a small enclosure can raise the internal temperature by several degrees, which is a calibration problem rather than a valve problem.

The deflection varies continuously with the applied voltage, so the opening does too. A solenoid is fundamentally an on-off device and needs pulse modulation or a pilot stage to approximate proportional behaviour, whereas the piezo element is already analogue. That is why they appear as pilots inside proportional pressure regulators.

The travel of the element, which is very small. Bending elements move tens of microns to a fraction of a millimetre, so orifice sizes and therefore flow rates stay low. Applications needing real flow use a piezo element as the pilot and let it drive a larger pneumatically actuated main stage.

Very long in switching terms, because there is no sliding seal and no armature impact to wear. The practical life limits are electrical - the element degrades under sustained high field and under humidity - and mechanical fatigue of the ceramic if it is driven beyond its rated deflection. Cycle life figures are typically an order above equivalent solenoid valves.

Clean and dry, more so than a solenoid valve of the same size. The orifices are small enough to be blocked by particulate that a larger valve would pass, and condensate on the element affects both its movement and its insulation. Filtration and drying immediately upstream belong in the specification rather than in a later retrofit.

Usually yes. The element wants a controlled voltage, often higher than the logic supply and with a defined charge and discharge behaviour, so manufacturers supply a matched driver or integrate one into the valve. Connecting a piezo valve to a standard solenoid output does not work and can damage the element.