In a Gas Compressor, interlocks are critical safety and operational controls that automatically shut down or prevent startup when unsafe or abnormal conditions occur.

Here’s a list of common/normal interlocks you’ll find in most centrifugal or reciprocating gas compressors (used in oil, gas, or process plants):

🔹 Startup Interlocks (Pre-Start Checks)

These must be satisfied before the compressor can start:

1. Lube oil pressure high enough – (e.g., ≥ 1.5 bar before start)
2. Seal oil pressure available (for dry gas seal or oil seal systems)
3. Cooling water available (intercooler, aftercooler flow)
4. No vibration trip active
5. No high bearing temperature alarm/trip
6. Suction and discharge valves open (if required by logic)
7. Anti-surge system healthy
8. Emergency stop not active
9. Compressor in local/remote auto mode (as required)
10. Power supply normal (no undervoltage/phase fail)

🔹 Running Interlocks (Trip Conditions)

These cause immediate shutdown of the compressor when triggered:

1. Low lube oil pressure
2. High lube oil temperature
3. High bearing temperature
4. High vibration
5. High axial displacement (thrust bearing)
6. High/low suction pressure
7. High discharge pressure
8. High differential pressure across filter (lube/seal oil)
9. Seal oil pressure low (below gas pressure margin)
10. Cooling water flow low
11. Motor overload / electrical fault
12. Emergency Stop (ESD signal)
13. Fire or gas detection in compressor area
14. Anti-surge trip or recycle valve failure
15. Compressor casing high temperature

🔹 Process-Related Interlocks

These protect the process or connected equipment:

1. Discharge pressure high → Recycle valve opens (anti-surge protection)
2. Suction pressure very low → Trip or unload
3. Knock-out drum high level → Trip
4. Seal gas differential pressure low → Trip
5. Seal gas supply failure → Trip

🔹 Shutdown Interlocks

Triggered manually or by system:

1. Manual Emergency Stop (ESD)
2. Plant Shutdown Signal (PSD)
3. Fire & Gas Trip
4. Motor protection relay trip

🔹 Optional/Condition-Based Interlocks

Depending on compressor type and control philosophy:

• Bypass valve not open at startup → inhibit start
• Seal system pressure difference not maintained → trip
• Process gas leak detection → trip
• High vibration twice in 10 minutes → shutdown