液压接头的控制元件(即各种液压阀)在液压系统中控制和调节液体的压力、流量和方向。根据控制功能的不同，液压阀可分为压力控制阀、流量控制阀和方向控制阀。压力控制阀又分为益流阀(安全阀)、减压阀、顺序阀、压力继电器等；流量控制阀包括节流阀、调整阀、分流集流阀等；方向控制阀包括单向阀、液控单向阀、梭阀、换向阀等。根据控制方式不同，液压阀可分为开关式控制阀、定值控制阀和比例控制阀。
The control elements of hydraulic joint (i.e. various hydraulic valves) control and regulate the pressure, flow and direction of liquid in the hydraulic system. According to the different control functions, the hydraulic valve can be divided into pressure control valve, flow control valve and direction control valve. The pressure control valve is divided into benefit flow valve (safety valve), pressure reducing valve, sequence valve, pressure relay, etc.; the flow control valve includes throttle valve, adjustment valve, diversion valve, etc.; the directional control valve includes one-way valve, hydraulic control check valve, shuttle valve, directional valve, etc. According to the different control methods, the hydraulic valve can be divided into on-off control valve, fixed value control valve and proportional control valve.