Stretch spring is a key part of the pneumatic valve, so we must carefully consider the range of the selection of stretch spring, stretch spring manufacturers range of key selection from the stability of the pneumatic valve, output force two levels to consider.

1. Selection of valve stability:

Select from the stability of the regulator, the stretch spring should be the harder the better, it not only to overcome slight oscillations, friction, and can make the valve core complex movement freely.

2. Selection of output force:

Because the output force of the actuator is the total net force of the actuator minus the tension, friction, and the softer the spring, the greater the output force. Therefore, a soft stretch spring (i.e. a small stretch spring category) should be selected for output force consideration.

3. Selection for special circumstances:

In case of large diameter, large pressure difference, containing particles and other occasions, the selection of its stretch spring range according to the detailed calculation to meet.

4. Comprehensive performance selection:

If from the stability of the selection, to choose a wide range of hard stretch spring; If from the point of view of the output force, and should use the stretch spring range of small soft stretch spring, the two are mutually contradictory, so should be considered comprehensively. A wide range of hard stretch springs is used as far as possible to satisfy the output force. The author suggests to make full use of the 250KPa air source of the positioner for the film regulating valve and to choose the 60-180kpa stretch spring. It has an output force of 60KPa for the gas opening valve and 250-180 = 70KPa for the gas closing valve. Its tensile spring range Pr is 180-60 = 120KPa. The output force of the traditional 20 ~ 100KPa stretch spring with 140KPa air source; The gas opening valve is 20KPa, the gas closing valve is 140-100 = 40KPa, and the stretch spring range Pr = 100-20 = 80KPa. No matter from the output force, stiffness, we propose to select 60 ~ 180KPa stretch spring range is far superior to the conventional stretch spring range.