使得主阀芯打开，①口到②口实现溢流，该压力为一级设定压力，当

③口施加一定压力后，①口到②口的溢流压力会相应提高，该压力为

二级设定压力。

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.