Air carrier Technician reported; while accomplishing an engine recovery cleaning on an ERJ-170; the technician opened the nitrogen supply valve and noticed the pressure increased from 15 psi to 80 psi causing damage to the air turbine starter.

Narrative

It was around XA:50 and since I had finished with my workload for the night; I decided to help do the comp wash on the LH engine on Aircraft X; since there wasn't anyone around at the time that felt comfortable running the wash cart. I thought myself familiar enough with the process to get the job done; except I had never set the wash cart up completely by myself before. On other occasions I had turned the water supply on and off using the lever on the tank; but I did not have experience setting up the nitrogen pressure for the tank. I had thought that since the gauge was at roughly 15psi and I was told before that 15-20 psi was the optimal range; that I was good and only needed to turn the water supply on and off from there.So; once the mechanic in the cockpit gave me the all clear to start running the cart; I did so; flipping the water supply on. A few seconds pass by and still the engine rpm doesn't change nor do I see water coming out of the engine. It was at this point that I look around; making sure I wasn't missing anything. My nitrogen gauge still read at roughly 15 psi and my water supply for the right tank was set to 'ON'; so I looked around a bit more and the only thing I could think of was the nitrogen supply bottle might be closed. As soon as I opened the nitrogen supply bottle; I noticed the psi had shot up from around 15 to 80 instantly. I could've been faster on the regulator; but I don't think that would've changed much since about a second after; I heard a loud grinding noise over the engine dry motoring. I smelled something burning; and saw white sparks shoot from the tail end of the engine as water finally came out. Someone else got the mechanic in the cockpit to shut the engine down while I shut the cart off.After all was said and done; the Air Turbine Starter (ATS) was in need of replacement; since there were many chunks of metal attached to the chip detector. Other mechanics came over to replace the ATS and I came to write this report while the information was still fresh in my mind.Suggestions: Ask for training on using GSE (Ground Support Equipment) if you are unsure; don't assume you got it; unless you want to blow up an Air Turbine Starter with an engine wash cart.