As a software developer with some years of experience, I seem to run into this same issue in one form or another, so I'l generalize it the best I can. 

Let's say I'm on 3 teams. Team A has given me enough work to keep me busy if they were my only team. Team B had a project that should have been completed a while back, but the client won't accept it for one reason or another, so I'm brought back in regularly to handle the client's issues. Team C maintains a legacy system that catches on fire sometimes and I'm called in to help put it out. 

All three are important and I have trouble finding someone else to pass the work onto. So, how do I juggle the 3 teams plus all the other business-related responsibilities?