The pressure supply, as well as the connection of the return flow of the main control blocks is made via a so-called P+R connection. This P+R connection is the same for main control blocks, whether pilot or pilot-direct, 8 – 12 – 16 – or 20 functions, and is flanged to the corresponding block. In the P+R connection there is a check valve in the R connection and a coarse dirt filter in the P connection. A valve is also installed to prevent the return pressure from exceeding the supply pressure.