In commissioning industrial ammonia and CO₂ refrigeration projects, we often see ICM motorized valves with perfectly good hardware, yet system pressure and liquid level keep fluctuating. Many people's first reaction is to suspect a faulty valve or controller. In reality, quite a few cases trace back to an oversized valve forced to operate long-term in a tiny opening range. This is not a valve quality defect; it's a system matching problem.
The ICM uses a V-notch regulating plug. Plug travel and flow rate are not linearly proportional. At small openings, an extremely slight movement of the plug causes a dramatic change in refrigerant flow; at large openings, the same plug travel produces a much gentler flow change.
When the valve is oversized and actual system load is low, the valve is forced to maintain 5% opening or even less for extended periods (for DN100–150 sizes, the recommended minimum opening is above 10%). The external EKE series controller's PID loop outputs adjustment commands based on pressure or level deviation, asking the ICM to fine-tune its opening. But the slightest plug movement swings the flow drastically — overshoot is almost inevitable: too much flow when opened a touch, then instantly too little when closed a touch. The controller can only keep correcting back and forth, which manifests as oscillating system pressure and level.
Secondary symptoms follow: the ICAD actuator frequently triggers the Boost function, the valve position keeps correcting back and forth, the event log fills with A9 valve position deviation alarms, and mechanical wear on the motor and plug seals accelerates.
Here's the key point: valve selection must not simply copy the site pipe DN size. You must calculate the Kv flow coefficient for actual operating conditions and match the function module, ensuring the valve still operates above the manufacturer's recommended safe opening even at minimum system load.
If a project already has this problem, the preferred fixes in order: first, replace with an internal function module with a smaller Kv value — the valve body itself can stay, no pipe cutting needed; second, optimize the controller PID parameters to reduce response sensitivity; third, use the ICAD software to limit the valve's minimum working opening, keeping it out of the dangerous small-opening zone.
— Wenzhou Phonetoo (en.phonetoo.cn), Danfoss IR distributor. Happy to compare field notes.