To convert energy between BuildCraft and PneumaticCraft, PneumaticCraft adds two machines: The Pneumatic Engine, which converts compressed air into BuildCraft’s MJ, and the Kinetic Compressor, which creates compressed air from MJ. For both you can select their efficiency (as server owner) in the config. By default it’s set to 40%.
The Pneumatic Engine is like any other BuildCraft engine. But this one runs on compressed air. It starts running from 5 bar, creates more MJ (and uses more air) at higher pressures. These different energy production stages can be seen as the engine color: blue = 4MJ/tick, green = 6MJ/tick, yellow = 8MJ/tick and red = 10MJ/tick. You can rotate it with a BuildCraft Wrench exactly like you would with any other BuildCraft engine.
-4x Compressed Iron Ingot
-1x Stone Gear
Yields 1x Compressed Iron Gear
-3x Compressed Iron Ingot
-2x Compressed Iron Gear
Yields 1x Pneumatic Engine
The Kinetic Compressor, like said earlier, converts BuildCraft’s MJ into compressed air. It consumes 1 up to 10 MJ/tick. It can’t be powered with a Redstone Engine. It’s rotatable with a BuildCraft Wrench.