HITORK Pneumatic control valve is a very common intelligent component in the production process. In the control system, pneumatic control valve will inevitably appear friction. So what is the impact of friction on pneumatic control valves?
Overcoming friction is one of the primary functions of the valve positioner. The friction of regulating valve mainly comes from two parts: packing and sleeve valve seal ring. If the stem is not smooth or the packing is too tight, friction between the stem and packing can be excessive. In high temperature occasions, the interference matching of graphite ring and sleeve is usually used to make the regulating valve meet the design sealing requirements. If the interference is too large or the sleeve ellipse is too large, the friction between the spool and the sleeve is too large. Because the static friction force is much greater than the dynamic friction, in the distance of a large range of action, the valve will jump, which is also known as peristalsis. Its fluctuation mechanism is as follows: when telesignal mutation (i.e. step signal) occurs, the negative deviation caused by friction is too large, and the overall effect of the positioner keeps increasing the output. When the static friction force increases enough to overcome, the valve acts. Because static friction is greater than dynamic friction, valve overshoot, negative deviation becomes positive deviation. The system is difficult to stabilize due to repeated overshoots. Aiming at the friction problem, some shifter manufacturers design high friction algorithm, which greatly reduces the occurrence of valve fluctuation.