The spring is the main part of the pneumatic valve. Here are some brief introductions:
First, the "standard spring range" error
The spring range refers to the membrane chamber pressure at which the pressure in the membrane chamber of the regulating valve during the static start to the full stroke, the letter is denoted by Pr. The commonly used spring range is 20~100KPa, 20~60KPa, 60~100KPa, 60~180KPa, 40~200KPa... Because the standard signal of the pneumatic instrument is 20~100KPa, the control valve manufacturers leave the factory according to the standard of 20~100KPa, this is Incorrect.
Second, the choice of spring range
The choice of the spring range is mainly from the stability and output force of the pneumatic valve.
1, the stability of the valve selection:
Select from the stability of the control valve, the spring should be as hard as possible, it not only overcomes slight oscillations, overcomes friction, but also allows the valve core to move freely.
2, the output force on the choice:
Because the output force of the actuator is the total force of the actuator minus the spring tension, friction force, and spring softening, the output force is greater. Therefore, the soft spring (ie, the small spring range) should be selected in consideration of the output force.
3, comprehensive performance on the choice:
If we choose from the stability, we must use a hard spring with a large range of springs; if we look at the output force, we should use a soft spring with a small range of springs, and the two are contradictory. Therefore, we should consider it comprehensively.
When the output force is satisfied, a hard spring with a large range is selected as much as possible. The author proposes to make full use of the gas source of the positioner 250 KPa for the diaphragm regulating valve and use a spring of 60-180 KPa. It has an output force of 60 KPa for the air opening valve and 250-180=70 KPa for the air closing valve, and its spring range Pr is 180-60=120 KPa. The output force of a conventional 20-100 KPa spring with a 140 KPa air supply is 20 KPa for the air opening valve and 140-100 = 40 KPa for the air closing valve with a spring range of Pr=100-20=80 KPa. Regardless of the output force and stiffness, we suggest that the spring range of 60 to 180 KPa is much better than the conventional spring range.
4, special circumstances to choose:
In case of large caliber, large differential pressure, particles, etc., the selection of the spring range is satisfied by detailed calculation.