Please excuse my ignorance.

But I have another few college / improver questions.

On a COOLING only system, I understand the 2 pipe principal - Suction/Discharge.

But on the 3 pipe heat pump system, I am getting slightly confused.

I felt 3 pipes on the return pipe run to the unit a Daikin VRV the other day, and am I right in saying that one is suction, one is hot gas and one is liquid ?.

Is this termed as MIXED phase ?.

On the 4 way reversing valve does it have input from the Hot Gas,Liquid and Suction as described above

In the ceiling voids I was told that there were BS boxes, can anyone explain the term BS,and how these actually work within the system please.

Thanks everyone for any help.