A station valve is required for every receiver. You may choose receivers with a built-in station valve or you may choose individual station T valves that are mounted near each receiver. These are often mounted above the receivers but some brands can be mounted on their side so they can be located behind or below receivers. They are easier to reach and they minimize overhead clutter.
How a Station T Valve Functions:
When the disc is seated in the closed position, the vacuum passes through the sequencing valve. When the valve receives a signal to load the receiver, the disc opens, allowing vacuum to pull material into the receiver. A reinforced filter disc, in the receiver, allows air to pass through it while keeping the pellets from being drawn into the vacuum line.