Tension spring is the key component of pneumatic valve, so we must carefully consider the range selection of tension spring. Xiaobian told us that the key to select the range of tension spring is the stability and output force of pneumatic valve.

1. Selection of valve stability:

From the stability of the control valve, the harder the tension spring is, the better. It can not only overcome the slight oscillation and friction, but also make the valve core move freely.

2. Output force selection:

Because the output force of the actuator is the total resultant force of the actuator minus the tension and friction force of the tension spring. The softer the tension spring is, the greater the output force will be. Therefore, considering the output force, the soft spring should be selected.

3. For special conditions, select:

In case of large diameter, large pressure difference and particles, the selection of the range of the tension spring can be satisfied according to the detailed calculation.

4. In terms of comprehensive performance, it is selected as follows:

If we choose from the stability, we should choose the hard stretching spring with a wide range of stretching springs; if we look at the output force, we should also use the soft stretching spring with a small range of stretching springs. The two contradict each other, so we should consider them comprehensively. Under the condition of satisfying the output force, a wide range of hard stretching springs should be used as far as possible. The author suggests that the 250kPa air source of positioner should be fully used for the diaphragm control valve, and the tension spring of 60 ~ 180kpa should be selected. It has an output force of 60kpa to the air opening valve and 250-180 = 70kpa to the air closing valve, and its stretching spring range PR is 180-60 = 120kPa. The output force of traditional 20-100kpa tension spring with 140kpa air source is 20KPa for air opening valve, 40kpa for air closing valve, and PR = 100-20 = 80kPa for tension spring. No matter in terms of output force and stiffness, the range of 60-180kpa tension spring is far superior to that of conventional tension spring.