(click to enlarge)
In this photo, I have shown a valve used as a pressure release valve, a manual pump, and three air tanks. I have shown them as a branch to the system instead of in line. Branches for components like this make it easier to add and work on certain problems.
The pressure release valve is used to release pressure when the system is not in use. A tube is attached to the center connection and when the system is pressurized, the lever is kept in the center position. Moving the lever either way releases pressure. Just remember to return the lever to the center position or else you will have a problem when trying to build pressure again. I don't like to store projects under pressure, so this allows me to quickly release pressure.
I like to build a manual pump into my systems. This is to have a way to quickly add pressure to the system to test actuators and other equipment in the system. It is not always necessary but can be convenient when it takes some work to get the compressor going.
Air tanks are great because it is a great way to store energy. The more tanks you add into the system, the less often the compressor will cycle to regain pressure. I wish I had many more.