原因：预紧力过小。

Reason: too small preload.

1. 热胀冷缩：在同一机械设备上，螺栓、垫片、法兰、填料函由于材料均不同，在同样温度变化幅度下，其热胀冷缩的速度各自不同，这样在温差下，原先的预紧力就会各自减小，通过彼此的重叠，此预紧力松弛程度会成几何级放大，导致泄漏;

The 1. expansion and contraction in the same machine, bolt, gasket, flange, stuffing materials are different because, in the same temperature range, the thermal expansion and contraction velocity is different, so in the temperature, the original preload will reduce their overlap with each other, and the pre tightening force relaxation the degree will be a geometric magnification, resulting in leakage;

2. 压力起伏：原理同上;

2. pressure fluctuation: the principle is the same as above;

3. 机械振动：原理同上;

3. mechanical vibration: the principle is the same as above;

4. 化学腐蚀：原理同上;

4. chemical etching: the principle is the same as above;

5. 填料函体积：原理同上。

5. stuffing box volume: the principle is the same as above.

原因：预紧力过大。

Reason: too much preload.

由于计算错误或不全面，选用预紧力过大的碟簧后，若其压力过大并超过垫片、螺栓材料本身的屈服极限后，同样导致泄漏。

As a result of incorrect calculation or incomplete, the choice of pre tension too large plate spring, if the pressure is too large and more than the gasket and bolt material itself, the yield limit, the same lead to leakage.

这种情况下必须用碟簧来补偿，其补偿力为大于最小密封所需要的预紧力，小于材料屈服极限75%。

In this case, the disc spring must be used to compensate for the pre tightening force greater than the minimum required for sealing. It is less than the material yield limit of 75%.

现实工作中，通常出现两种错误：

There are usually two kinds of errors in real work:

1. 选择压力过小：根据螺栓预紧力物理特性，若预紧力松弛30%，则达不到密封所需的最小值，等于没有安装碟簧;

1., the choice of pressure is too small: according to bolt pretension physical characteristics, if the preload relaxation 30%, then can not reach the minimum required for sealing, equal to no installation disc spring;

2. 选择压力过大：若超过碟簧弹性屈服极限或使阀杆抱死，导致碟簧行程超过75%内锥高度导致永久变形，等于人为放大螺栓预紧松弛力，危害更大。

2. selection pressure: if more than the spring elastic yield limit or stem locking, resulting in more than 75% disc spring cone height leads to permanent deformation, equal to artificially enlarged bolt pretightening force relaxation, more harm.