The Pneumatic Generator can generate IndustrialCraft 2 EU/$ from compressed air/$. This is a tier two machine, indicated by its minimal working pressure of 15 bar. By default it has an efficiency of 40%, but this can be changed in the config/$.
Without any Speed Upgrades/$, it outputs at a rate of 32 EU/tick; with one upgrade inserted: 128 EU/tick and with two: 512 EU/tick.
The air usage (mL/tick) is:
output rate / E * 400/$
where E/$ is efficiency as a percentage. E.g. for default efficiency of 40%, and an output rate of 32EU/tick, air usage = 32 / 40 * 400 = 320mL/tick/$.
An important factor that influences efficiency is the Generator's temperature/$. The Generator needs to be cooled/$, or its efficiency will drop as the temperature rises, up to the point where no air is generated at all.
Crafting a Pneumatic Generator