1. Throttle valve (1) A throttle valve is a valve that controls fluid flow by changing the throttle cross-section or throttle length. By connecting a throttle valve in parallel with a check valve, a one-way throttle valve can be formed. Throttle valves and one-way throttle valves are simple flow control valves. In a hydraulic system with a fixed displacement pump, a throttle valve and an overflow valve can be combined to form three types of throttle speed control systems: the inlet throttle speed control system, the return throttle speed control system, and the bypass throttle speed control system.

(2) ICOMEON Valves believes that the throttle valve lacks a flow negative feedback function and cannot compensate for speed instability caused by load changes. It is generally only used in situations where load changes are not significant or where speed stability is not highly required. It is a hydraulic pressure control valve that primarily serves as a constant pressure overflow and safety protection function in hydraulic equipment.

(3) The performance requirements for the throttle valve are: 1. Wide flow adjustment range, smooth variation in flow pressure difference; small internal leakage, and if there is an external leakage oil port, the external leakage should also be small; small adjustment torque, and sensitive action.

一、节流阀

（1）节流阀是通过改变节流截面或节流长度以控制流体流量的阀门。将节流阀和单向阀并联则可组合成单向节流阀。节流阀和单向节流阀是简易的流量控制阀，在定量泵液压系统中，节流阀和溢流阀配合，可组成三种节流调速系统，即进油路节流调速系统、回油路节流调速系统和旁路节流调速系统。 

（2）针型阀生产厂家阿卡盟阀门认为节流阀没有流量负反馈功能，不能补偿由负载变化所造成的速度不稳定，一般仅用于负载变化不大或对速度稳定性要求不高的场合。一种液压压力控制阀。在液压设备中主要起定压溢流作用和安全保护作用。 

（3） 对节流阀的性能要求是：1、流量调节范围大，流量压差变化平滑；内泄漏量小，若有外泄漏油口，外泄漏量也要小；调节力矩小，动作灵敏。

 二、溢流阀 

（1）针型阀门生产厂家阿卡盟阀门认为溢流阀定压溢流作用：在定量泵节流调节系统中，液压油泵提供的是恒定流量。当系统压力增大时，会使流量需求减小。此时溢流阀开启，使多余流量溢回油箱，保证溢流阀进口压力，即泵出口压力恒定（阀口常随压力波动开启）。 

（2）针型阀门生产厂家阿卡盟阀门认为安全保护作用：系统正常工作时，阀门关闭。只有负载超过规定的极限（系统压力超过调定压力）时开启溢流，进行过载保护，使系统压力不再增加（通常使溢流阀的调定压力比系统最高工作压力高10％～20％）。 

（3） 针型阀门生产厂家阿卡盟阀门认为实际应用中一般有：作卸荷阀用，作远程调压阀，作高低压多级控制阀，作顺序阀，用于产生背压（串在回油路上）。溢流阀一般有两种结构：1、直动型溢流阀 。2、先导型溢流阀。

(1) ICOMEON Valves, a manufacturer of needle valves, believes that the pressure relief function of an overflow valve is as follows: In a throttling adjustment system with a fixed displacement pump, the hydraulic oil pump provides a constant flow rate. When the system pressure increases, the flow demand decreases. At this time, the overflow valve opens to allow excess flow to overflow back to the oil tank, ensuring that the inlet pressure of the overflow valve, that is, the pump outlet pressure, remains constant (the valve port often opens with pressure fluctuations).  

(2) The needle valve manufacturer, ICOMEON Valves, believes in the safety protection function: When the system is operating normally, the valve is closed. Only when the load exceeds the specified limit (system pressure exceeds the set pressure) will the overflow valve open to provide overload protection, preventing the system pressure from increasing further (typically, the set pressure of the overflow valve is set to be 10% to 20% higher than the maximum working pressure of the system).  

(3) ICOMEON Valves, a manufacturer of needle valves, believes that in practical applications, needle valves are generally used as unloading valves, remote pressure regulating valves, high and low pressure multi-level control valves, sequence valves, and for generating back pressure (connected in series on the return oil circuit). There are generally two types of relief valves: 1. Direct-acting relief valve. 2. Pilot-operated relief valve.