阀是锅炉、压力容器.压力管道等承压设备保护装置。阀的工作原理和操作规范了解很重要。在上海高压阀门看来：阀是直接依靠介质压力产生的作用力来克服作用在阀瓣上的机械载荷使阀开启的，作用在阀瓣上的机械载荷主要来自重锤或弹簧，这种几乎是固定的机械载荷。要想保证阀的密封性能，必须阀座密封面和阀瓣密封面的平整度和表面粗糙度有严格的要求。
Safety valve is boiler, pressure vessel, pressure pipe and other pressure equipment protection device. It is very important to understand the working principle and operation specification of safety valve. In the view of Shanghai high pressure valve: safety valve is the direct force produced by the medium pressure to overcome the mechanical load on the valve flap to open the safety valve, the mechanical load on the valve flap mainly from weight or spring, which is almost constant mechanical load. In order to ensure the sealing performance of the safety valve, the valve seat sealing surface and the valve seal surface smoothness and surface roughness must be strictly required.

阀的工作原理：
Working principle of safety valve:
以弹簧式阀为例：工作原理是压力=压强X面积。压力就是弹簧的压力，面积就是密封面的面积。当作用在密封面上的压强乘以密封面的面积形成的向上的推力大于弹簧的压力，弹簧被压缩，密封面打开，将压力通过泄压孔排出。
Take the spring safety valve as an example: the working principle is the pressure = pressure X area. Pressure is the pressure of spring, the area is the area of the sealing surface. When the pressure acting on the sealing surface is multiplied by the area of the sealing surface, the upward thrust is greater than the pressure of the spring, the spring is compressed, the sealing surface is opened, and the pressure is discharged through the pressure relief hole.
当设备内的压力超过规定的工作压力并达到阀的开启压力时，内部介质作用于闹瓣上面的力大于加载机构施加在它上面的力，于是  阀瓣离开阀座，阀开启，设备内的介质即通过阀座排出。此时内压作用于阀瓣上面的力又小于加载机构施加在它上面的力，阀瓣又紧压着阀座，介质停止排出，设备保持正常的工作压力继续运行。所以，阀是通过阀瓣上介质作用力与加载机构作用力的消长，自行关闭或开启以达到防止设备超压的目的。
When the equipment inside the pressure exceeds the pressure of work and achieve the safety valve opening pressure, the internal medium acting on the flap above downtown the force is greater than the loading mechanism applied on top of it, then leave the seat valve, safety valve opens, equipment in the medium is discharged through the valve seat. The force acting on the valve clack is less than the force exerted on it by the loading mechanism, and the valve tightly presses the valve seat, the medium stops discharging, and the equipment keeps the normal working pressure and continues to run. Therefore, the safety valve is through the valve on the medium force and the force of the loading and unloading mechanism of growth and decline, self closing or opening, in order to achieve the purpose of preventing equipment overpressure.
当阀的整定压力大于被保护系统的工作压力时，阀门处于关闭状态，这时作用在阀瓣上的力有弹簧预紧力F，方向向下，介质的作用力，方向向上，再就是阀座对阀瓣的托力（密封力），这个密封力在密封面上所产生的比压力，保证了阀关闭件间有了必需的密封性。
When the safety valve set pressure is greater than the protection system of the working pressure, the valve is in the closed state, the role of the force on the valve spring preload F, downward direction, medium force, direction, and is the seat of the valve (sealing force), uplift forces the sealing force in the sealing surface than the pressure generated, ensuring the safety valve closure with the required sealing.
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