I. Structure and Failure Correspondence
The core feature that distinguishes twin screw pumps from other conveying equipment: screws are responsible for conveying, gears for synchronization, seals for isolation, and bearings for centering. These four core structures determine the overall equipment performance, and deviation in any link will trigger systematic failures.
1.1 Core Structural Division (Core Basis for Maintenance)
1. Synchronous Timing Gear System: It controls the phase, clearance and synchronous speed of twin screws, serves as the core factor preventing screw friction and ensuring ultra-low shear performance. 80% of wear failures are rooted in gear phase deviation.
2. Twin Screw Rotor Assembly: It forms closed cavities to push materials. The mirror precision, thread clearance and surface smoothness directly determine conveying efficiency and material protection capability.
3. Dual-End Sterile Sealing System: It isolates the medium from the transmission end, adapts to solvent corrosion, high-temperature sterilization and sterile working conditions, and is the high-frequency part prone to leakage, pollution and explosion-proof failure.
4. Bearing and Drive Shaft System: It controls axial play and radial runout. Excessive runout will directly cause gear meshing misalignment, screw scraping and eccentric seal wear.
5. Explosion-Proof & Sanitary Pump Cavity: Adopting streamline dead-space-free structure, it determines GMP cleaning effect. Cavity deformation, scratches and dead spaces will lead to excessive microorganisms and residual material deterioration.
1.2 Mandatory Working Condition Constraints for Maintenance
The maintenance of twin screw pumps in health food and explosion-proof extraction workshops is different from that of ordinary industrial pumps, which must meet three constraints simultaneously: mechanical operation accuracy, GMP sterile cleaning specifications, and explosion-proof electrical safety specifications. Ordinary industrial maintenance cannot adapt to harsh working conditions such as solvent corrosion, high-temperature SIP sterilization, active bacteria protection and static explosion prevention, which is the core reason for frequent rework of equipment in high-standard scenarios.
II. Phenomena, Root Causes and Maintenance Judgment Standards
2.1 Insufficient Flow, Pressure Attenuation and Weak Conveying Capacity
Phenomena: The motor operates normally without overload, but the discharge volume decreases, feeding speed slows down, and pipeline pressure fails to reach the rated process value, resulting in reduced conveying efficiency for both high and low viscosity materials.
Core Root Causes: ① Timing gear wear leads to increased screw clearance, severe internal medium backflow and sharp drop of volumetric efficiency; ② Screw mirror scouring wear and thread wear cause failure of cavity tightness; ③ Air leakage from inlet pipeline and slight internal seal leakage; ④ Pump cavity scaling accumulates and occupies effective cavity volume; ⑤ Long-term low-speed operation leads to material retention and cavity residue accumulation.
Maintenance Judgment: Simple cleaning cannot restore flow performance. It is necessary to disassemble the pump, calibrate screw clearance, detect gear wear loss and repair cavity surface smoothness.
2.2 Severe Pressure Fluctuation, Unstable Filling Accuracy and Uneven Batch Quality
Phenomena: The outlet pressure fluctuates erratically, the filling weight deviation of oral liquid and soft capsules exceeds the standard, paste conveying is intermittent, and obvious flow pulse occurs.
Core Root Causes: Excessive bearing axial play, uneven gear meshing clearance, screw phase deviation, pipeline air intake, unstable seal flushing pressure, and mismatched frequency conversion parameters with medium viscosity.
2.3 Abnormal Pump Noise, Severe Vibration and Operation Shaking
Abnormal Noise Classification and Corresponding Failures: Clicking gear impact noise → gear pitting, oil shortage and meshing misalignment; metal friction noise → excessive small screw clearance and cavity scraping; dull vibration noise → bearing wear and misalignment; intermittent stalling noise → particle jamming and foreign matter residue in the cavity.
Core Inducements: Uncalibrated timing phase after maintenance, long-term dry running, bearing fatigue wear, emulsified and deteriorated gear oil, and installation misalignment.
2.4 Seal Leakage, Solvent Escape and Material Dripping
This is the most frequent failure of twin screw pumps, and 90% of leakage problems are caused by mismatched materials and improper assembly. Under organic solvent working conditions, ordinary NBR rubber seals will rapidly swell, precipitate impurities and crack to cause leakage; excessive seal compression burns the end face while insufficient compression leads to poor sealing; high-temperature SIP sterilization causes seal aging and hardening; blocked flushing pipelines result in seal dry wear and failure.
2.5 Abnormal Material Quality: Probiotic Inactivation, Fish Oil Stratification and Particle Breakage
Working-Condition-Specific Failure: It only occurs in health food and microbial fermentation scenarios. The root causes include turbulent flow generated by disordered screw clearance, abnormally high rotating speed caused by equipment failure, material deterioration due to retention in pump cavity dead spaces, and degradation of active ingredients caused by excessive friction temperature rise. Essentially, it is the failure of ultra-low shear structure after improper maintenance.
2.6 Explosion-Proof Specific Failures: Excessive Static Electricity and Flammable Gas Alarm
Incomplete restoration of equipotential grounding after maintenance, damaged seals of explosion-proof junction boxes, aging conductive layers of anti-static hoses, and solvent vapor intrusion into electrical cavities will lead to failure of workshop explosion-proof acceptance and potential flammable and explosive hazards.
2.7 Excessive Microorganisms and Unqualified CIP Cleaning
Offset and protruding gaskets after assembly, scratched and rough pump cavity mirror surfaces, misplaced parts and residual materials in dead spaces will breed molds and miscellaneous bacteria, directly resulting in GMP verification failure.
III. Standardized Disassembly and Maintenance Process for Explosion-Proof Clean Workshops (Compliance Mandatory)
For twin screw pump maintenance, disassembly determines cleanliness and assembly determines precision. Rough disassembly is the root cause of all subsequent failures, and standardized disassembly procedures must be implemented in explosion-proof clean workshops.
3.1 Pre-Maintenance Safety Lockout (Mandatory for Explosion-Proof Workshops)
Strictly implement power lockout and tagout to completely cut off the power supply; close inlet and outlet valves, discharge residual materials and organic solvents in the pump cavity and pipelines, and release pressure for static placement; ventilate in advance for ethanol and acetone extraction working conditions and operate only after the flammable gas concentration reaches the standard; disinfect the external equipment, isolate the clean maintenance area, and separate special clean tools from mechanical tools to avoid cross-contamination.
3.2 Standard Disassembly Sequence (Outside-In, Cleanliness First Then Mechanics)
Disconnect CIP cleaning pipelines and material conveying pipelines → remove sanitary clamps and sterile gaskets → disassemble explosion-proof electrical wiring and grounding lines with marked storage → detach pump cover and take out screw assembly → disassemble mechanical seals and flushing components → dismantle gearbox and inspect gear and bearing conditions.
Core Taboo: Do not pry stainless steel screws and pump cavities with iron tools to avoid damaging the electrolytic polishing mirror surface and forming permanent sanitary dead spaces.
3.3 Graded Processing Specifications for Disassembled Parts
Stainless steel wetted parts: undergo sterile cleaning, passivation, disinfection and independent storage; rubber seals and gaskets: scraped disposablely without reuse; mechanical seals, bearings and gears: precisely inspected for repair or replacement; explosion-proof electrical accessories: seal inspection with immediate replacement of damaged parts.
IV. Special Precision Repair Standards for Five Core Components (Core Maintenance Know-How)
4.1 Special Maintenance of Mechanical Seals (Core of Leakage Elimination)
Mechanical seals are wearing parts with strong working condition adaptability, and universal replacement is prohibited. PTFE encapsulated seals must be adopted for ethanol/acetone solvent working conditions; EPDM seals for water-based probiotic working conditions; HNBR seals for high-temperature paste working conditions; FKM fluororubber seals for strong corrosion working conditions. NBR nitrile rubber is strictly prohibited for organic solvent scenarios. During maintenance, inspect the flatness of moving and static ring end faces for no cracks or carbonization, and uniform spring elasticity; strictly control seal compression amount and match sterile flushing pipelines to eliminate dry wear failure.
4.2 Precision Repair and Calibration of Screw Rotor Assembly
Inspect screw mirror smoothness, thread wear and shaft end bending deformation; polish and restore slight scratches on the mirror surface, and replace severely worn or bent screws in pairs. Mixing new and old screws is forbidden, otherwise it will cause phase disorder, friction abnormal noise and flow attenuation. The core maintenance point is to calibrate the zero-contact safe clearance of screws relying on timing gears to restore ultra-low shear conveying performance.
4.3 In-Depth Inspection and Maintenance of Timing Gear System
As the phase core of twin screw pumps, gears need key inspection for pitting, tooth breakage, wear, meshing clearance and synchronization accuracy. Completely replace food-grade explosion-proof lubricating grease if the gearbox grease is emulsified, blackened or water-infiltrated; replace worn gears in pairs instead of single replacement; recalibrate gear meshing clearance and screw phase to eliminate cavity scraping and wear fundamentally.
4.4 Maintenance of Bearing and Drive Shaft System
Inspect bearing clearance, rolling element wear and jamming abnormal noise, and replace failed bearings immediately; calibrate drive shaft straightness and coaxiality, control axial play and radial runout within standard ranges to solve equipment vibration, eccentric seal wear and gear meshing misalignment problems.
4.5 Sanitary Repair of Pump Body Cavity
Repair cavity scratches, scouring wear and scaling dead spaces, restore mirror polishing grade, ensure full fillet and dead-space-free structure, meet the requirements of automatic CIP cleaning and GMP sterility, and eliminate material residue and excessive microorganisms.
V. Precision Assembly and Calibration Standards (Key to Maintenance Success)
80% of rework problems stem from non-standard assembly and uncalibrated clearance. Parts replacement without calibration equals invalid maintenance.
1. Screw Clearance Calibration: Precisely adjust twin screw meshing clearance to ensure zero metal contact, no jamming and no friction during operation, balancing volumetric efficiency and ultra-low shear performance.
2. Gear Timing Calibration: Lock the screw zero phase, calibrate gear backlash and synchronization accuracy to ensure consistent rotating speed and constant phase of twin screws.
3. Seal Compression Calibration: Strictly control the compression stroke of mechanical seals to avoid end face burning caused by excessive compression and leakage caused by insufficient compression.
4. Axial Play Calibration: Control bearing axial play to eliminate pressure fluctuation and unstable filling accuracy.
5. Sanitary Gasket Assembly: Install gaskets flat and centered without offset, protrusion or depression to completely eliminate cleaning dead spaces.
6. Explosion-Proof Structure Restoration: Fasten explosion-proof surfaces diagonally with uniform torque, recheck the overall grounding resistance ≤4Ω to restore anti-static and explosion-proof tightness.
7. Coaxiality Calibration: Correct the coaxiality between pump and motor to avoid equipment wear caused by long-term eccentric operation.
VI. Working-Condition-Specific Maintenance Specifications (Dual Standards of GMP Cleanliness and Explosion-Proof Safety)
6.1 GMP Maintenance Specifications for Food and Health Food Industries
Adopt sterile maintenance tools to prevent iron impurity pollution; prohibit the use of industrial lubricants and ordinary seals; ensure no dust, fiber or impurities during the whole assembly process; complete CIP cleaning verification after maintenance to confirm no material residue and microbial growth, meeting GMP cleaning verification requirements.
6.2 Special Maintenance Specifications for Explosion-Proof Workshops
Avoid scratching and damaging explosion-proof flameproof surfaces; completely restore the seals of explosion-proof junction boxes and cable glands; prohibit unauthorized modification of electrical structures and cancellation of grounding lines; recheck static grounding performance and explosion-proof tightness after maintenance to prevent solvent vapor intrusion into electrical cavities and ensure compliant safe production in workshops.
VII. Graded Maintenance System: Daily Inspection, Regular Maintenance and Annual Overhaul
7.1 Daily Inspection (Per Shift)
Check equipment abnormal noise, vibration, temperature rise, seal leakage and solvent peculiar smell; record operating pressure, flow rate and rotating speed; inspect the integrity of grounding lines and clean residual materials on the pump body in a timely manner.
7.2 Weekly Maintenance
Recheck grounding resistance and explosion-proof seal status; verify the patency of seal flushing pipelines; fasten pipeline clamps and bolts; troubleshoot hidden dangers of air intake and material leakage.
7.3 Monthly Maintenance
Check gearbox oil level and grease status; calibrate frequency conversion operating parameters; inspect aging of anti-static hoses; correct equipment operation stability.
7.4 Quarterly In-Depth Maintenance
Disassemble and inspect seal wear, screw clearance and gear meshing status; verify bearing precision; complete CIP cleaning effect verification; check the tightness of explosion-proof system.
7.5 Annual Overhaul (Full Equipment Maintenance)
Completely disassemble and inspect the whole equipment, replace all aging seals, gaskets and vulnerable parts; renew food-grade gear lubricating grease; precisely recalibrate timing phase and screw clearance; repair cavity mirror surface; fully restore explosion-proof and GMP sanitary performance to restore the equipment to brand-new operating status.
VIII. Ten High-Frequency Industry Maintenance Misunderstandings (Key On-Site Pitfalls)
1. Pure parts replacement without calibration: Replacing seals, screws and bearings without timing clearance calibration leads to recurrent wear failures in a short time.
2. Mixed use of general seal materials: Ordinary rubber seals applied to solvent working conditions cause material swelling and pollution, as well as leakage and explosion-proof hidden dangers.
3. Single gear replacement: Mismatched meshing of new and old gears leads to failure of synchronization accuracy and continuous screw scraping.
4. Dry running test after maintenance: Dry friction instantly burns mechanical seals, which is the primary human-induced cause of seal damage.
5. Reuse of aging gaskets and seals: Cause cleaning dead spaces, excessive microorganisms and material leakage.
6. Use of industrial lubricating grease: Pollute sterile materials and lead to GMP audit failure.
7. Rough disassembly damaging mirror and explosion-proof surfaces: Form permanent sanitary dead spaces and failure of explosion-proof performance.
8. Ignoring coaxiality calibration: Eccentric operation accelerates wear of bearings, screws and seals.
9. No cleaning verification after maintenance: Residual impurities cause batch material pollution and scrapping.
10. Only mechanical maintenance without explosion-proof restoration: Incomplete grounding and seal restoration leads to failure of safety supervision acceptance.
IX. Post-Maintenance Commissioning and Compliance Acceptance Standards
9.1 No-Load Commissioning Standards
Jog operation without stalling, abnormal noise or vibration; normal temperature rise during no-load operation without abnormal heating of gearbox and pump body; smooth and uniform manual shaft rotation without local jamming.
9.2 Loaded Process Commissioning Standards
Low-speed protective operation for viable bacteria and paste materials with complete particles, no breakage and no stratification; no residue after high-speed CIP cleaning; pressure fluctuation ≤±2%, stable filling accuracy and flow rate reaching rated standards.
9.3 Dual Compliance Acceptance Standards
Explosion-Proof Safety Acceptance: Qualified grounding resistance, complete explosion-proof seals, no static electricity accumulation and no hidden dangers of solvent leakage.
GMP Sanitary Acceptance: No material residue, no cleaning dead spaces, qualified microorganisms, no metal impurity pollution and no seal precipitation.