Low pressure air pens are the state-of-the-art technology in the fossil preparation world. They run optimally at very low pressures, and are incredibly powerful for their size. The optimal working pressure of the ZOIC ZPT-TR T-Rex is just 2.5 Bar or 35 PSI, and its internal design gives it an exceptionally low air consumption of just 5l/min or 0.2 CFM.
These tools are supplied with a pressure regulator so you don't have to adjust anything your compressor end. The reason that they run at such low pressures is their shear power. Whilst, in theory, they will happily run at 6 Bar or 90 PSI, this will shatter the tungsten carbide nib under the force of the piston. It could also damage the internals of the pen (so please don't put it into self-destruct mode). Tungsten carbide is used to make nibs for fossil preparation because it is very abrasion resistant (rock being an abrasive surface) - we use a very high grade of tungsten carbide which means that it will only break if used improperly (like vamping your T-Rex up too much!).