Diaphragm couplings (also known as disc couplings) are essential components in precision motion control systems. With their zero backlash, high torsional rigidity, and low inertia, they are the preferred choice for encoders, resolvers, servo motors, stepper motors, and instrumentation applications.

This guide explains how diaphragm couplings work, the difference between single and double diaphragm designs, and how to select the right model for your application.

1. What Is a Diaphragm Coupling?

A diaphragm coupling is a flexible coupling that uses one or more stainless steel diaphragms to transmit torque while compensating for misalignment. It consists of:

• Two metal hubs – typically aluminum or steel

• A stainless steel diaphragm – that connects the hubs

Torque is transmitted through the diaphragm, which flexes to accommodate angular and axial misalignment while maintaining high torsional rigidity and zero backlash.

💡 Diaphragm couplings are widely used in drive systems for encoders, instrumentation, lead screws, small pumps, feed rollers, and anywhere a light to medium-duty, torsionally flexible coupling is required.

2. Single Diaphragm vs Double Diaphragm – Which One Do You Need?

Selection guideline:

• Choose single diaphragm when space is limited, high torsional rigidity is required, and shafts are well-aligned with no significant parallel misalignment.

• Choose double diaphragm when parallel misalignment must be accommodated.

3. Key Advantages of Diaphragm Couplings

4. Materials – Why Aluminum + 304 Stainless Steel?

The DS series uses a combination of high-strength aluminum alloy for the hubs and 304 stainless steel for the diaphragm:

5. Applications Where Diaphragm Couplings Excel

6. How to Select the Right Diaphragm Coupling

Step 1: Determine Your Torque Requirement

• Calculate the torque your application requires.

• Select a coupling with adequate torque capacity.

• DS series covers 1–80 N·m.

Step 2: Determine Single or Double Diaphragm

• Single diaphragm (DS): For well-aligned shafts, high rigidity, compact spaces.

• Double diaphragm: For applications requiring radial misalignment compensation.

Step 3: Match Shaft Diameters

• Measure your shaft diameters.

• Select a model with a bore range that accommodates your shafts.

• H7 bore tolerance is recommended for precision fit.

Step 4: Consider Space Constraints

• Measure available space for the coupling (outer diameter and length).

• DS series offers compact sizes from 19mm OD.

Step 5: Evaluate Misalignment

• Determine the expected angular and axial misalignment.

• DS series accommodates angular (1°) and axial misalignment.

Step 6: Consider Speed Requirements

• Verify the coupling’s maximum speed exceeds your operating speed.

• DS series offers speeds up to 10000 RPM.

Step 7: Consider Keyway Requirements

• For applications requiring keyways, add “K” to the model number.

• Example: DS-26×26-7K×8K – both bores with keyways.

7. Real‑World Example – Encoder Upgrade

A machine builder was experiencing position errors on a servo-driven system due to backlash in their existing coupling. The coupling also had high inertia, limiting acceleration.

They switched to Apex Coupling DS series single diaphragm coupling (aluminum hubs, 304 stainless steel diaphragm, zero backlash, low inertia). Results:

• Position errors eliminated – zero backlash

• Acceleration improved – low inertia

• Maintenance eliminated – no lubrication required

• Accuracy improved – H7 precision bore

• Service life extended – 304 stainless steel diaphragm provided excellent fatigue resistance

8. Installation & Maintenance Tips

1. Clean shafts – Remove oil, grease, and debris before installation.

2. Check alignment – Even with misalignment compensation, keep within recommended limits.

3. Tighten clamping screws evenly – Use a torque wrench in a star pattern.

4. No lubrication required – Coupling is maintenance-free.

5. Periodic inspection – Check for wear, cracks, or deformation in the diaphragm.

6. Keep clean – Remove dust and debris to prevent premature wear.

7. Keyway option – For keyway applications, ensure proper key fit.

9. Selection Checklist

• □ 

  Type: DS – single diaphragm coupling

• □ 

  Structure: Single diaphragm – for well-aligned, space-limited applications

• □ 

  Material: Aluminum hubs + 304 stainless steel diaphragm

• □ 

  Backlash: Zero backlash – precision applications

• □ 

  Bore: H7 tolerance – match your shaft diameters

• □ 

  Keyway: Add “K” if required (e.g., DS-26×26-7K×8K)

• □ 

  Fastening: Clamping screw – secure, even clamping force

• □ 

  Misalignment: Angular (1°) and axial – verify capacity

• □ 

  Speed: Up to 10000 RPM – match your motor speed

• □ 

  Torque: 1–80 N·m – ensure it exceeds your requirement

• □ 

  Maintenance: Maintenance-free – no lubrication

• □ 

  Application: Encoders, servo motors, stepper motors, lead screws, instrumentation

10. Conclusion

The DS series aluminum single diaphragm coupling from Apex Coupling offers the perfect combination of zero backlash, high torsional rigidity, low inertia, and maintenance-free operation for precision motion control applications. With aluminum alloy construction, 304 stainless steel diaphragm, clamping screw fastening, and H7 bore precision, it is the ideal solution for encoders, resolvers, servo motors, stepper motors, lead screws, instrumentation, and light to medium-duty drive systems.

👉 Need a diaphragm coupling for your precision application? Contact us with your model, bore, and torque requirements.