使得主阀芯打开，P到T实现溢流。该类型的阀一般具有较高的启闭

率，内泄漏小，适用于高压力、大流量的液压系统。

When the pressure at "p" reaches 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 P to T.This type of

valve can withstand a certain amount of back pressure,has

high opening and closing rate Suitable for the hydraulic 

system of high pressure and large flow.