1. Description of the problem and scope of application
High Discharge Temperature (HDT) is one of the most common causes of emergency shutdown of screw compressors. This symptom indicates a thermal imbalance in the air compression system.
Field of application: Oil-filled industrial screw compressors.
Classification of criticality:
- Critical: Temperature >110°C (automatic emergency shutdown, risk of screw block destruction).
- Majorna: Temperature 100°C - 110°C (work in the temperature degradation zone of lubricant).
- Minor: Temperature 90°C - 100°C (requires monitoring, checking the cleanliness of coolers).
2. Safety measures
WARNING: Perform the Lockout/Tagout (LOTO) procedure before starting any work. The compressor contains high pressure components, hot surfaces (>90°C) and dangerous voltage. Use personal protective equipment (PPE): safety glasses, heat-resistant gloves, special shoes. Do not open the oil tank caps or filters until the system pressure has been reduced to atmospheric.
3. Necessary diagnostic tools
| Tool | Specification/Model | Range | Purpose |
|---|---|---|---|
| Infrared camera | FLIR or similar, Sec. >160x120 | -20°C to +500°C | Detection of local overheating (thermostat, cooler) |
| Digital multimeter | True RMS (e.g. Fluke 87V) | V/A/Ohm | Checking temperature sensors (RTD/NTC) |
| Manometer (calibrated) | Accuracy class 1.0 | 0-25 bar | Checking the pressure drop on the oil filter |
| Anemometer/Air flow meter | Winged | 0-20 m/s | Measurement of cooling air flow |
4. Initial assessment checklist
| Parameter | What to check | write down |
|---|---|---|
| Lubricant | The level in the viewing window, signs of foaming | Level (%), color, presence of extraneous odors |
| Cooler | The cleanliness of the ribbing, the presence of external contamination | Condition (clean/dirty) |
| environment | Room temperature, ventilation | Air inlet temperature (°C) |
| History | Alarm Log | Time and value of the last 5 errors |
5. Systematic diagnostic algorithm
- Checking external factors:
- Indoor temperature >40°C? -> Check the ventilation of the room.
- Air intake blocked? -> Clean the entrance blinds.
- Checking the cooling system:
- Is the temperature at the outlet of the cooler significantly lower than the inlet temperature? -> No: Clogged cooler or low air flow.
- Checking the oil circuit:
- Is the temperature of the thermostat housing uniform? -> No: the thermostat is stuck in the closed position.
- High pressure drop across the oil filter? -> Replace the filter.
6. Matrix of malfunctions and causes
| Symptom | Probable reasons | Diagnostic test | Expected result (confirmation) |
|---|---|---|---|
| HDT > 105°C | Thermostat jamming | Compare the temperature of the thermostat nozzles (IR camera) | Large temperature difference (cold/hot) |
| HDT > 105°C | Contaminated cooler | Measure ΔT between air inlet and outlet | Small ΔT or uneven heating |
| HDT > 105°C | Low oil level | Visual inspection | The level is below the minimum mark |
| HDT > 105°C | Defective sensor (false signal) | Check the resistance of the sensor with a multimeter | Deviation from table values |
7. Root cause analysis
7.1. Thermostat jamming
The thermostat regulates the flow of lubricant through the cooler. If it jams in the closed position, the lubricant circulates in a small circle (bypass), bypassing the cooler. This leads to a rapid increase in the injection temperature. Confirmed by the IR camera: the thermostat housing on the cooler side remains cold while the outlet is hot.
7.2. Contamination of the cooler
External contamination (dust, oil, fluff) on the fins of the cooler significantly reduces the efficiency of heat exchange. Internal contamination (sediment, soot) limits the flow of lubricant. In both cases, the temperature of the lubricant returning to the screw block remains too high.
8. Troubleshooting procedures
- Replacing the oil filter:
- Relieve the pressure in the system.
- Unscrew the old filter, clean the seat.
- Lubricate the seal of the new filter with clean grease.
- Tighten the filter by hand (do not use a wrench for tightening).
- Replacing the thermostat:
- Isolate the thermostat, drain the grease from the unit.
- Disassemble the case, remove the element.
- Install a new element, check the integrity of the seals.
- Check tightness after start-up.
9. Preventive measures
| The reason | Strategy | Monitoring method | Interval |
|---|---|---|---|
| Pollution | Regular blowing of the cooler | Visual inspection, ΔT control | Every week |
| Lubricant degradation | Lubricant quality analysis | Laboratory analysis (acid number, viscosity) | Every 2000 hours |
| Filters | Planned replacement | Monitoring ΔP | According to the maintenance regulations |
10. Spare parts and components
| Description | Specification | When to replace | Category UNITEC |
|---|---|---|---|
| Oil filter | According to the model | Every 2000-4000 hours | Consumables |
| Thermostatic element | According to OEM | Every 8000 hours | Components |
| Lubricant | Synthetic for screw compressors | Every 4000-8000 hours | Lubricating materials |
All necessary spare parts are available in our catalog: https://www.unitecd.com/e-catalog/
11. Links
- ISO 8573 (compressed air quality).
- OEM (specific compressor manufacturer) operating instructions.
- Internal security protocols of UNITEC-D GmbH.
