The Heart of Industrial Refrigeration Plants: NH3 (Ammonia) screw compressors operate under high pressure at 1,450 – 2,950 RPM continuously for tens of thousands of hours. Adhering to standard technical maintenance protocols not only prevents catastrophic unplanned downtime risking hundreds of tons of frozen cargo, but is also a critical imperative for occupational safety and toxic refrigerant containment.
1. Detailed Inspection Checklist for Screw Compressors
| Inspection Item | Acceptance Criteria | Measurement Method & Equipment | Corrective Action if Out of Spec |
|---|---|---|---|
| Bearing Vibration Amplitude | ≤ 2.8 mm/s RMS (ISO 10816-3) | FFT vibration spectrum analysis via Fluke 810 | Re-align coupling or replace with matched precision bearings |
| Motor Shaft Alignment | Misalignment ≤ 0.05 mm | Laser alignment via SKF TKSA Series | Re-shim motor base and torque bolts to factory spec |
| Total Acid Number (TAN) in Oil | ≤ 0.10 mg KOH/g | Laboratory spectrophotometric oil sampling | Full oil drain & flush; install new micro-fiber oil filter |
| Differential Pressure Across Oil Filter | ΔP ≤ 0.8 bar | Danfoss differential pressure transducer | Replace magnetic and particle filter element |
| Stator Winding Insulation Resistance | ≥ 50 MΩ (tested at 1,000V DC) | Digital Megohmmeter insulation tester | Bake & dry motor windings or apply insulating varnish |
2. Zero-Leak NH3 Refrigerant Recovery Protocol During Overhauls
Anhydrous Ammonia (NH3 / R717) is corrosive and acutely irritating. The Tan Long engineering team strictly enforces IIAR international safety standards before opening any compressor casing:
- Step 1 - Isolation Valve Lockout: Tightly close suction, discharge, oil return, and liquid injection stop valves. De-energize main circuit breakers and apply Lockout/Tagout (LOTO) security padlocks.
- Step 2 - Evacuation & Refrigerant Recovery: Use an oil-free recovery unit to pump out residual gas into high-pressure receivers or condensers until internal compressor pressure reaches -0.05 MPa vacuum.
- Step 3 - Nitrogen Purge & Neutralization: Inject dry nitrogen (N2) through the casing to sweep trace NH3 vapor through a water scrubber neutralization tank (dissolving NH3 into safe ammonium hydroxide).
- Step 4 - Ambient Gas Concentration Verification: Validate with multi-gas digital detectors that ambient NH3 is below 25 ppm OSHA threshold before unbolting rotor covers.
3. Vital Guidelines for NH3 Screw Compressor Lubrication Oils
DO: Use Synthetic PAO / Alkylbenzene Oils
Dedicated synthetic base oils (e.g., CPI-4600-68, Mobil Gargoyle Arctic SHC 226) offer pour points down to -54°C, preventing wax agglomeration in evaporators while maintaining durable hydrodynamic film on screw lobes.
DON'T: Never Mix Incompatible Oil Formulations
Never mix mineral oils with synthetic POE/PAG formulations. Incompatible additive packages react chemically to produce tar sludge, choking oil filters and causing rotor seizure within 48 operational hours.
4. International Standard Periodic Maintenance Schedules
| Maintenance Tier | Operating Hours | Core Inspection & Servicing Scope |
|---|---|---|
| Tier 1 Initial Service | After first 500 – 1,000 hours | Replace initial run-in oil filter, re-torque base anchor bolts, verify shaft laser alignment. |
| Tier 2 Annual Service | Every 5,000 hours (~1 year) | Spectrometric oil viscosity & wear metal test, replace primary oil filter, inspect mechanical seal, recalibrate safety pressure transducers. |
| Tier 3 Major Overhaul | Every 20,000 – 25,000 hours | Extract rotor assembly to inspect lobe wear, replace all precision thrust & radial bearings, adjust axial clearances, replace capacity slide valve and Teflon gasket sets. |
5. Overhaul & Rebuilding Steps Executed by Tan Long
- Safe Refrigerant Containment: Use dedicated recovery systems to transfer gas into high-pressure receivers, lock out isolation valves, and evacuate casing.
- Specialized Mechanical Teardown: Match-mark all components, remove mechanical seal housing, thrust bearing retainers, and male/female rotor pairs using hydraulic pullers.
- Micron-Precision Dial Gauge Inspection: Measure rotor lobe profile tolerances, sleeve bearing clearances, and axial thrust play against OEM factory tolerances.
- Reassembly & Laser Alignment: Reassemble the rack with shaft alignment tolerances under 0.03mm to eliminate startup vibration harmonics. Explore our 24/7 industrial cold storage maintenance services.
Technical FAQs: NH3 Screw Compressor Maintenance
1. Bao lâu thì cần phải thay dầu bôi trơn máy nén lạnh NH3 screw một lần?
Dầu bôi trơn máy nén NH3 chuyên dụng (gốc khoáng Hydrotreated hoặc gốc tổng hợp PAO) nên được thay mới sau mỗi 5.000 đến 8.000 giờ vận hành hoặc ngay khi kết quả xét nghiệm dầu cho thấy chỉ số axit TAN > 0.1 mg KOH/g hoặc dầu bị đổi sang màu nâu đen.
