当P口压力达到设定压力后，先导阀芯首先被打开，由此产生的压差

使得主阀芯打开，P到T实现溢流。该类型的阀反向可以承受一定的

背压,启闭率较高，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.