Compressor drives present coupling specification challenges that go beyond the standard pump or fan application. The torque character of the driven load — smooth for centrifugal and screw types, highly pulsating for reciprocating types — creates torsional excitation that must either be absorbed by the coupling or addressed through torsional analysis to avoid resonance. The starting method adds peak torque loading. And the consequence of a coupling failure on a compressor — in an oil and gas facility, a refrigeration system, or a compressed air network — can range from inconvenient to catastrophic. The F-type flexible tyre coupling handles the majority of screw and centrifugal compressor applications effectively. The EP-JZM diaphragm coupling is specified where maintenance-free operation, high temperature, and torsional analysis-driven stiffness selection are all required simultaneously.
Compressor Types and Their Coupling Demands
Centrifugal Compressor
Smooth torque output. High speed — typically 3,000–12,000 RPM at the compressor shaft. Zero-backlash disc or diaphragm coupling required at high speeds. Torsional analysis recommended for large units above 500 kW.
Screw Compressor
Moderate torque ripple at rotor pitch frequency. Standard flexible tyre or jaw coupling suitable up to 200 kW. VSD operation requires confirmation that coupling stiffness is appropriate for the control bandwidth.
Reciprocating Compressor
Pulsating torque at piston stroke frequency — the most demanding coupling application. Soft elastomeric coupling to absorb pulses or torsional analysis to specify coupling stiffness for resonance avoidance. High service factor mandatory.
Diaphragm Compressor
Very low speed, very high torque per stroke. Typically belt or gear driven — coupling may not be in the primary torque path. Where a coupling is used, heavy-duty flexible type with high service factor required.
Coupling Selection by Compressor Type
| Compressor Type | Speed Range | Recommended Coupling | Service Factor | Special Requirement |
|---|---|---|---|---|
| Centrifugal (direct drive) | 3,000–12,000 RPM | Disc or diaphragm coupling | 1.25–1.50 | Torsional analysis >500 kW; balance to G2.5 |
| Centrifugal (via gearbox) | Motor speed to gearbox | Flexible tyre or disc coupling | 1.25–1.50 | Balance grade to suit motor speed |
| Screw (DOL start) | 1,450–3,000 RPM | F-type flexible tyre coupling | 1.75–2.25 | 92A PU spider standard |
| Screw (VSD driven) | Variable RPM | F-type flexible tyre (80A or 92A) | 1.75–2.00 | Check coupling stiffness vs VSD bandwidth |
| Reciprocating 2-cyl (DOL) | 750–1,500 RPM | F-type flexible tyre (NR or 80A PU) | 2.50–3.00 | Torsional analysis >50 kW recommended |
| Reciprocating single-cyl (DOL) | 500–1,000 RPM | Soft flexible tyre (NR or 80A PU) | 3.00–3.50 | Torsional analysis mandatory >30 kW |
Torsional Analysis for Reciprocating Compressor Drives
A torsional analysis for a reciprocating compressor coupling requires: motor rotational inertia (J_motor, in kg·m²); coupling torsional stiffness (kt, in Nm/rad); compressor crankshaft and flywheel rotational inertia (J_compressor); number of cylinders and firing order; rated RPM and operating speed range. From these inputs, the system’s natural torsional frequencies are calculated and compared to the compressor’s excitation frequencies at each operating speed.
The output is a determination of whether any excitation frequency falls within the continuous operating speed range at a vibratory torque amplitude that exceeds the coupling’s or crankshaft’s fatigue limit. If it does, the coupling torsional stiffness is adjusted (by changing elastomeric element grade) until the resonance moves outside the operating range or below the fatigue limit. Our engineering team performs torsional analysis at no charge for compressor coupling applications above 30 kW — contact us with your compressor and motor specifications to initiate the review.
Frequently Asked Questions
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