A diaphragm coupling is a type of high-performance, flexible coupling that transmits torque and rotation between two shafts while accommodating misalignment and absorbing system vibrations. Unlike gear or grid couplings that rely on sliding contact, diaphragm couplings utilize one or more flexible metallic membranes (diaphragms) as the sole flexible element. This design philosophy makes them a premier choice for demanding applications where reliability, precision, and maintenance-free operation are critical, such as in turbines, compressors, pumps, and high-speed machinery.
Design and Working Principle
The core of a diaphragm coupling consists of three main components:
Flexible Diaphragm Pack(s): These are thin, precision-stamped discs or packs of discs made from high-strength, fatigue-resistant metals like stainless steel (AISI 300 series) or Inconel. The diaphragms are designed with a specific contour—often a series of concentric arcs or a convoluted shape—that allows them to flex elastically. This flexibility is the key to accommodating misalignment.
Hubs: The two hubs are attached to the driving and driven shafts, typically using keyed, splined, or clamp-style connections. They are rigidly bolted to the outer diameter of the diaphragm pack(s).
Center Member or Spacer: A center spacer tube, often called the "spool piece," connects the two sets of diaphragms. This component provides the necessary separation between the two shafts and can be manufactured to various lengths. The diaphragms are bolted to each end of this spacer.
How it Works: Torque is transmitted from the first hub, through the flexing diaphragm, into the center spacer, through the second diaphragm, and finally to the second hub. When shaft misalignment (angular, parallel, or axial) occurs, the diaphragms undergo controlled elastic deformation (bending or stretching) rather than friction or sliding. This deformation generates the flexibility needed to accommodate the misalignment while maintaining constant velocity and transmitting torque efficiently.
Key Advantages and Characteristics
Diaphragm couplings offer a distinct set of benefits that make them suitable for critical applications:
Zero Backlash and High Torsional Stiffness: The all-metal, one-piece flexing element provides a direct, non-sliding connection, ensuring precise angular positioning and repeatability. This is essential for servo drives and high-speed machinery.
Maintenance-Free and Lubrication-Free: With no moving parts in contact, there is no wear, no need for lubrication, and no risk of contamination. This reduces lifecycle costs and makes them ideal for clean or sealed environments.
High Speed and High Torque Capability: Their balanced, all-metal construction allows them to operate at very high rotational speeds (often exceeding 20,000 RPM) while transmitting significant torque for their size.
Excellent Misalignment Capacity: They can accommodate angular, parallel, and axial misalignment, typically in combinations defined by the manufacturer's specifications. The axial growth of connected equipment (from thermal expansion) is easily absorbed.
Long Service Life and Predictable Performance: The diaphragms are designed for high-cycle fatigue resistance. Their life can be predicted based on the applied misalignment and torque, and they fail safely (usually by cracking, not shattering) without releasing debris.
Electrical Isolation (Optional): Some designs incorporate non-conductive materials in the bolt sleeves or spacers to provide shaft-to-shaft electrical isolation, preventing damaging circulating currents.
Common Applications
Diaphragm couplings are the coupling of choice in industries where downtime is costly and reliability is paramount:
Aerospace: Jet engine starters, auxiliary power units (APUs), and flight control systems.
Energy & Power Generation: Gas turbines, steam turbines, compressors, and generator sets.
Marine & Naval: Main propulsion systems, pump drives, and auxiliary machinery.
Oil & Gas: Pipeline compressors, offshore platform pumps, and gas turbine drivers.
Industrial Machinery: High-speed pumps, centrifuges, fans, and precision machine tool spindles.
