Double diaphragm couplings (also known as double disc couplings) are essential components in precision motion control systems. With their zero backlash, high torsional rigidity, and superior misalignment compensation, they are the preferred choice for servo motors, encoders, stepper motors, and instrumentation applications.

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

1. What Is a Double Diaphragm Coupling?

A double diaphragm coupling consists of:

• Two metal hubs – typically aluminum or steel

• Two stainless steel diaphragms – connected by a center spacer

• Clamping screw fastening – for secure shaft connection

Torque is transmitted through the diaphragms, which flex to accommodate angular, radial, and axial misalignment while maintaining high torsional rigidity and zero backlash. The double diaphragm design allows the two disc packs to bend in opposite directions, providing superior compensation for parallel misalignment.

💡 Double 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. They are particularly suited for applications with frequent starting, reversing, and high reliability requirements.

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

Selection guideline:

• Choose double diaphragm when radial (parallel) misalignment must be accommodated.

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

3. Key Advantages of Double Diaphragm Couplings

4. Materials – Why Aluminum + 304 Stainless Steel?

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

5. Applications Where Double Diaphragm Couplings Excel

6. How to Select the Right Double Diaphragm Coupling

Step 1: Determine Your Torque Requirement

• Calculate the torque your application requires.

• Select a coupling with adequate torque capacity.

• DL series covers 1–80 N·m.

Step 2: Determine Single or Double Diaphragm

• Double diaphragm (DL): For applications requiring radial misalignment compensation.

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

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).

• DL series offers compact sizes from 19mm OD.

Step 5: Evaluate Misalignment

• Determine the expected angular, radial, and axial misalignment.

• DL series accommodates angular (1.5°), radial (0.12-0.55mm), and axial misalignment.

Step 6: Consider Speed Requirements

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

• DL series offers speeds up to 10000 RPM.

Step 7: Consider Keyway Requirements

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

• Example: DL-26×35-7K×8K – both bores with keyways.

7. Real‑World Example – Servo Motor Upgrade

A machine builder was experiencing position errors on a servo-driven system due to backlash in their existing coupling. The coupling also could not accommodate the radial misalignment caused by thermal expansion.

They switched to Apex Coupling DL series double diaphragm coupling (aluminum hubs, 304 stainless steel double diaphragm, zero backlash). Results:

• Position errors eliminated – zero backlash

• Misalignment accommodated – double diaphragm compensated for radial, angular, and axial deviations

• Maintenance eliminated – no lubrication required

• Accuracy improved – H7 precision bore

• Service life extended – 304 stainless steel diaphragms 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 diaphragms.

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: DL – double diaphragm coupling

• □ 

  Structure: Double diaphragm – for applications requiring radial misalignment compensation

• □ 

  Material: Aluminum hubs + 304 stainless steel diaphragms

• □ 

  Backlash: Zero backlash – precision applications

• □ 

  Bore: H7 tolerance – match your shaft diameters

• □ 

  Keyway: Add “K” if required (e.g., DL-26×35-7K×8K)

• □ 

  Fastening: Clamping screw – secure, even clamping force

• □ 

  Misalignment: Angular (1.5°), radial, 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: Servo motors, encoders, stepper motors, lead screws, instrumentation

10. Conclusion

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

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