"Working on pneumatic relays can actually be difficult if you don't know the proper procedures. At my job, we used pneumatic relays to switch air signals from one source to another. Because of this, it is a top priority to always keep safety in mind because of the high pressures you are dealing with. When I work on a pneumatic relay, I visually inspect first to spot any obvious issues. If I don't see anything, I'll review the schematics before I start troubleshooting so that I can understand how everything is related. On one particular job I did all of that and still couldn't figure out what the issue was. Sometimes you can go through all the steps and it still isn't obvious what the problem is. I checked for any erratic functioning components, loose manual operations, and excessive air leakage. In the end, the problem was some unidentified pressure levels, but it took a lot of going back and forth to figure out that this was the cause of the problems. It helps to have previous experience with pneumatic relays so that you know the types of things to look for."