[cwl1979]

The hose pressure kicks the compressor on and off then the hard line will has the pressure relief valve on it to protect the pumptroller and prevent the the tank from over pressure. They just plumbed them together. Those should actually be separated. If that pressure valve were to fail the tank pressure could exceed what the rubber diaphragm in the pump control can handle and blow it out. then cause the compressor to run non stop till fixed.