The gas proportional valve detection equipment displays flow values that fluctuate frequently, sometimes suddenly spike to a large level and then return to zero, making it impossible to test stably. What should be done?

1. Analysis of the Cause of the Problem

Based on your description (restarting after power cut off temporarily restores the valve, replacing the proportional valve body is ineffective), the quality issues of the proportional valve itself can basically be ruled out. The root of the problem lies in the cleanliness of the air source and particulate matter in the air path.

This equipment uses gas mass flow control valves (MFC) or precision proportional control valves, which are mostly hard-sealed structures internally (such as metal valve cores and valve seats). When the compressed air source contains particles larger than 5μm (such as pipeline rust, welding slag, dust, or even raw material debris), these particles can get stuck between the sealing surfaces of the valve core and the valve seat, preventing precise reset of the valve core. At this point, the controller continuously increases or decreases the drive current to try to reach the set flow, but the valve core jams, causing the actual opening to fluctuate between large and small, reflecting fluctuations in flow values or even full scale. The electromagnetic force disappears immediately after power is cut off, and particles may temporarily leave the sealing surface due to airflow disturbances. Therefore, after restarting, the device can briefly recover, but after a few minutes of operation, the particles get stuck again and the fault reappears.

Additionally, there is a relatively rare cause: the PWM (pulse width modulation) signal of the proportional valve drive circuit is interfered with by high-power devices such as frequency converters, causing distortion of the drive waveform. However, this usually does not resolve with a power outage or restart, so your case prioritizes air source contamination.

2. Detailed Investigation and Solutions

Step 1: Check the air source treatment device (most important)

1. Locate the three-part air source treatment at the front end of the equipment's air inlet (usually including filter, pressure regulating valve, and oil mist). Observe whether there are obvious black or red particles at the bottom of the transparent cup on the filter.

2. Operation method: Close the main air source valve, release the filter cup, and remove the filter element for inspection. If the filter element surface turns black and contains hard particles, it indicates severe air source pollution.

3. Solution: Immediately replace the precision filter element with a filtration accuracy of 5μm or higher (the original equipment may be equipped with a 40μm coarse filter and needs to be upgraded). It is recommended to install a secondary filter: connect a condensing filter with a precision of 0.01μm in series at the front end of the equipment's air inlet.

Step 2: Thoroughly purge the pipeline

Even after replacing the filter element, particles that have entered the upstream pipeline of the proportional valve may still jam again.

1. Remove the proportional valve inlet connector, use clean compressed air (pressure 0.4-0.6MPa) to purge the pipeline upstream outward for more than 30 seconds.

2. Operating method: Connect one end of the equipment's air intake pipeline to the air source, wrap the other end with waste cloth, and blow in sections until no visible particles are ejected.

Step 3: Clean or replace the proportional valve (if stuck)

If the above operation still does not work properly, it indicates that particles remain inside the proportional valve.

1. Valve removal and cleaning: Carefully disassemble the proportional valve in a dust-free environment (note the order of parts), soak the valve core assembly in anhydrous ethanol, and clean with an ultrasonic cleaner for 5-10 minutes. After taking it out, dry it with clean air and reassemble it.

2. Direct replacement: If the valve remains unstable after cleaning, it is recommended to replace it directly with a new proportional valve and complete both steps one and two simultaneously.

Step 4: Check the source of the gas supply

Check whether galvanized pipes are used for gas supply pipes (which are prone to rust); it is recommended to switch to copper or stainless steel pipes. At the same time, confirm whether the compressor outlet is equipped with a high-efficiency oil removal filter.

3. Daily maintenance recommendations to prevent problems from recurring

• Inspect and replace the precision filter element every 3 months, and drain any accumulated water from the filter every month.

• The factory-configured air supply treatment triad must be retained before the equipment air inlet and cannot be omitted.

• It is recommended to hang an "Air Source Cleanliness Inspection Record Sheet" inside the pneumatic cabinet and sign it after each filter element replacement.