In vacuum applications piezo valves are used for precise admittance of gases at low flow rates and where baking is required. The usual construction is a piezo element stack one end of which is attached to the valve housing. The other end has a hard metal tip that opens and closes in proximity to an orifice of the correct size for the gas flow range. They are very fast and have low hysteresis especially as compared with solenoid proportioning control valves. The driver usually consists of a voltage multipier which produces up to about 150 volts. The semiconductor grade valves of this type go for well over $1000.
On the subject of fuel injectors, I have a prototype valve assembly that uses a standard injector (Bosch or equivalent). The trick is in the driver circuit as the drive must be stepped to avoid burning the valve out. There will be an article in "the Bell Jar" within 6 months on this type of valve. If anyone is really interested I have some references and I can provide some info on the driver electronics.
When using these valves it is important to flush the innards with a solvent as they are lubricated and the lubricant will form a barrier at low pressure differentials causing the flow to cease.
Steve
Created on Thursday, February 22, 2001 9:36 PM EDT by Steve Hansen