I. Leakage Issues

Seal Failure

Symptom: Liquid/gas leakage at valve body joints or spool seats.

Causes:

Wear of O-rings/NBR seals due to high temperature or corrosion (e.g., NBR seals aging above 100°C).

Scratches on the spool or seat surface from impurities (particle size >5μm).

Solutions:

Replace seals with materials compatible with the medium (e.g., PTFE for corrosive fluids, silicone for food-grade applications).

Polish the spool and seat (surface roughness Ra ≤0.8μm) and install a 10-20μm upstream filter.

Threaded Joint Leakage

Symptom: Leakage at threaded connections during pressure testing.

Causes: Inadequate thread engagement, damaged threads, or improper sealant application.

Solutions:

Apply PTFE tape or anaerobic sealant (e.g., Loctite 567) with 2-3 layers, ensuring 6-8 threads are engaged.

Replace damaged threads or use flanged connections for high-pressure systems (≥10MPa).

II. Valve Failure to Open/Close

Mechanical Jamming

Symptom: The valve cannot be opened/closed manually or electrically, with abnormal noise during operation.

Causes:

Sediment accumulation (e.g., rust, scale) in the valve body, jamming the spool.

Deformation of the valve stem due to excessive torque (e.g., over-tightening during installation).

Solutions:

Disassemble and clean the valve body, using ultrasonic cleaning for stubborn deposits.

Install a strainer upstream and use torque wrenches to tighten stems within specified limits (e.g., 15-20N·m for DN20 valves).

Electromagnetic Actuator Failure

Symptom: Electric drain valves show no response to control signals, with heated coils.

Causes: Coil burnout (open circuit), broken wires, or stuck armature cores.

Solutions:

Test coil resistance with a multimeter (should match the nominal value, e.g., 24V DC coil resistance ~50Ω).

Replace damaged coils and check for foreign objects in the armature cavity (e.g., iron filings).

III. Abnormal Noise and Vibration

Cavitation Noise

Symptom: High-pitch buzzing during valve operation, with visible bubbles in the medium.

Causes: Excessive pressure drop (ΔP >3MPa), leading to liquid vaporization and collapse.

Solutions:

Install a pressure relief valve at the outlet to maintain ΔP ≤2MPa.

Use valves with anti-cavitation trim (e.g., multi-stage pressure reduction cages).

Flow-Induced Vibration

Symptom: Pipeline vibration and rattling sounds during valve opening.

Causes: Unstable flow due to improper valve sizing (e.g., oversized valve causing low flow velocity).

Solutions:

Reselect the valve with a suitable Cv value (flow coefficient) to maintain optimal velocity (1-3m/s for liquids).

Install vibration dampers or rigid supports on pipelines (spacing ≤1.5m for DN50 pipes).

IV. Control Inaccuracy (for Proportional Drain Valves)

Signal Transmission Error

Symptom: The valve opening does not match the control signal (e.g., 4-20mA signal corresponds to inconsistent flow).

Causes: Electromagnetic interference (EMI), loose wiring, or sensor calibration drift.

Solutions:

Use shielded cables (e.g., RVVP 4×0.75mm²) and ground the shield at the control cabinet.

Re-calibrate the valve with a pressure/flow meter, adjusting the PID parameters (e.g., proportional band ≤5%).

Slow Response

Symptom: Delayed valve opening/closing (response time >10s for electric valves).

Causes: Worn seals increasing friction, or insufficient pilot pressure (for pneumatic valves).

Solutions:

Replace seals and apply silicone-based lubricant (e.g., Dow Corning 111) to moving parts.

Check and maintain pilot pressure within the specified range (e.g., 0.4-0.7MPa for pneumatic actuators).

V. Corrosion and Material Degradation

Medium-Induced Corrosion

Symptom: Pitting or rust on the valve body, with reduced sealing performance.

Causes: Incompatible material with the medium (e.g., carbon steel valves in acidic environments).

Solutions:

Replace with corrosion-resistant materials (316L stainless steel for acids, Hastelloy for strong alkalis).

Apply anti-corrosion coatings (e.g., zinc-nickel plating, thickness ≥15μm) for coastal or chemical plant applications.

Hydrogen Embrittlement (for Hydrogen Systems)

Symptom: Cracking of valve components under low stress, with no visible corrosion.

Causes: Hydrogen diffusion into metal lattices, reducing ductility (common in carbon steel at high pressure).

Solutions:

Use hydrogen-resistant materials (316L stainless steel, compliance with ISO 15848-1).

Avoid cold working of components and perform stress relief annealing (e.g., 650°C for 2 hours).