使得主閥芯打開，①口到②口實現(xiàn)溢流，該壓力為一級設定壓力，當

③口施加一定壓力后，①口到②口的溢流壓力會相應提高，該壓力為

二級設定壓力。

When the pressure of port ①reaches the valve setting ,the 

pilot spool starts to open,Next the main spool opening 

because of the pressure drop between inside and outside of

main spool, Realize overflow from port ① to port ②, This

pressure is the first level setting one, When a certain

pressure is applied to port ③, The overflow pressure from

port ① to port ② will increase accordingly, This pressure

is the secondary.