SJM Type Double Flexible Diaphragm Coupling: engineering overview
This page reorganizes the technical information for SJM Type Double Flexible Diaphragm Coupling around the decisions a buyer or engineer normally has to make: duty, shaft interface, alignment, installation envelope, inspection and model selection. All model values are retained in the reference blocks below.
Torque is carried through thin metallic diaphragm elements that flex elastically to accommodate limited shaft displacement. Because the torque path is metallic and does not rely on sliding gear teeth or an elastomer spider, the coupling can provide high torsional stiffness, zero-backlash behavior and clean operation without routine lubrication.
Key Features & Design Characteristics
Torsionally stiff transmission
Metal diaphragm elements transmit torque with limited rotational wind-up compared with elastomeric designs.
No routine lubrication
The flexible metallic element operates without grease lubrication at the flexing element.
Misalignment capability
Diaphragm flexure accommodates specified shaft displacement while maintaining a precise torque path.
Low-maintenance structure
Routine checks focus on fasteners, hubs, diaphragm condition and alignment rather than lubricant replacement.
How this version is configured
The diaphragm pack should flex within its designed range rather than being used to correct large installation errors. Angular and axial displacement produce cyclic stress in the membranes, while shaft spacing and intermediate members influence lateral critical speed. High-speed applications therefore require attention to balance, runout and the complete rotor system, not only the nominal torque rating.
- A double-flex diaphragm arrangement uses two flexible planes and can accommodate a wider combination of angular, axial and parallel displacement.
Selection sequence for a real machine
Establish the design torque from normal and transient loads, then verify the coupling speed, bore capacity, hub connection, axial allowance and angular compensation. Single- and double-flex arrangements are not interchangeable in every installation: double-flex configurations are generally chosen when direct parallel-offset accommodation is required, while single-flex versions are useful where the system geometry controls radial displacement.
- Define continuous torque, starting torque and any short-duration peak load instead of selecting from motor power alone.
- Confirm rotational speed and check whether balance, centrifugal loading or critical-speed limits affect the chosen size.
- Match every shaft interface: bore diameter, key or locking method, hub length, flange pilot, bolt pattern and available assembly clearance.
- Review angular, axial and parallel displacement separately. A coupling that tolerates one form of movement may have a much lower limit for another.
- Check the surrounding equipment for guards, brakes, bearings, seals and maintenance access before freezing the final outside diameter and overall length.
- Use the exact model matrix for the final dimensional decision; do not interpolate a bore, torque or speed value that is not listed.
Technical Specifications & Dimensions
Use the tables below as the dimensional and model reference. Confirm bore, shaft fit, speed, torque and installation envelope before final selection.
| Criterion | SJM Double | DJM Single |
|---|---|---|
| Diaphragm packs | 2 (with spacer) | 1 |
| Axial compensation | ±1.6–±16.4 mm | ±0.8–±8.2 mm |
| Angular compensation | Up to 2° | Up to 1° |
| Direct radial compensation | 0.5–3.0 mm | Indirect only |
| Overall length | Longer (spacer C) | Shorter |
| Long shaft spans | Preferred choice | Limited |
| Size | Nom. Torque N·m | Max Speed rpm | Bore d mm | D mm | A mm | B mm | L mm | C (spacer) mm | Axial mm | Angle | Radial mm | Weight kg |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 00 | 9,800 | 20,000 | 3–20 | 57 | 4.9 | 20 | 100 | 60 | ±1.6 | 2° | 0.5 | 0.7 |
| 01 | 33,000 | 20,000 | 5–22 | 68 | 6.1 | 26 | 141 | 89 | ±1.6 | 2° | 0.5 | 1.2 |
| 02 | 90,000 | 20,000 | 6–32 | 81 | 6.6 | 26 | 141 | 89 | ±1.6 | 2° | 0.5 | 1.9 |
| 03 | 173,000 | 18,000 | 8–35 | 93 | 8.4 | 29 | 160 | 102 | ±2.4 | 2° | 0.6 | 2.9 |
| 04 | 245,000 | 15,000 | 10–42 | 104 | 11.2 | 34 | 195 | 127 | ±2.8 | 2° | 0.7 | 4.7 |
| 05 | 420,000 | 13,000 | 15–50 | 126 | 11.7 | 42 | 211 | 127 | ±3.2 | 1°30′ | 0.7 | 7.1 |
| 06 | 772,000 | 12,000 | 20–60 | 143 | 11.7 | 48 | 223 | 127 | ±3.6 | 1°30′ | 0.8 | 10.8 |
| 07 | 1,270,000 | 10,000 | 25–75 | 168 | 16.8 | 58 | 243 | 127 | ±4.0 | 1°30′ | 0.8 | 16.3 |
| 08 | 2,080,000 | 10,000 | 30–82 | 194 | 17.0 | 64 | 268 | 140 | ±4.4 | 1°30′ | 0.9 | 24.7 |
| 09 | 3,328,000 | 9,000 | 30–95 | 214 | 21.6 | 77 | 306 | 152 | ±4.8 | 1°30′ | 0.9 | 32.5 |
| 10 | 4,900,000 | 8,000 | 40–108 | 250 | 23.9 | 89 | 356 | 178 | ±5.2 | 1°30′ | 1.0 | 50.0 |
| 11 | 6,368,000 | 6,300 | 52–118 | 276 | 27.2 | 102 | 382 | 178 | ±5.6 | 1°30′ | 1.2 | 75.0 |
| 12 | 8,900,000 | 6,300 | 60–110 | 276 | 17.5 | 128 | 409 | 153 | ±3.6 | 1° | 1.2 | 72.2 |
| 13 | 15,280,000 | 5,000 | 60–135 | 308 | 19.0 | 160 | 492 | 172 | ±4.0 | 1° | 1.2 | 120.0 |
| 14 | 25,410,000 | 4,700 | 60–155 | 350 | 21.5 | 182 | 554 | 190 | ±4.0 | 1° | 1.2 | 175 |
| 15 | 37,130,000 | 4,300 | 60–160 | 375 | 24.0 | 198 | 620 | 224 | ±4.0 | 1° | 1.3 | 234 |
| 16 | 47,120,000 | 3,900 | 70–180 | 410 | 29.5 | 214 | 682 | 254 | ±4.4 | 1° | 1.3 | 306 |
| 17 | 57,000,000 | 3,500 | 70–190 | 445 | 29.5 | 225 | 720 | 270 | ±4.4 | 1° | 1.4 | 369 |
| 18 | 63,186,000 | 3,500 | 80–205 | 470 | 31.0 | 248 | 770 | 274 | ±4.8 | 1° | 1.5 | 448 |
| 19 | 82,590,000 | 3,200 | 90–230 | 512 | 32.0 | 278 | 843 | 287 | ±4.8 | 1° | 1.6 | 596 |
| 20 | 102,100,000 | 2,800 | 90–255 | 556 | 32.5 | 305 | 902 | 292 | ±5.2 | 1° | 1.8 | 763 |
| 21 | 126,070,000 | 2,450 | 100–265 | 588 | 34.0 | 318 | 948 | 312 | ±5.4 | 1° | 1.8 | 919 |
| 22 | 146,350,000 | 2,150 | 100–275 | 630 | 34.5 | 332 | 1008 | 344 | ±5.6 | 1° | 2.0 | 1068 |
| 23 | 173,830,000 | 2,000 | 100–290 | 655 | 35.5 | 348 | 1052 | 356 | ±6.0 | 1° | 2.0 | 1235 |
| 24 | 200,000,000 | 1,400 | 210–305 | 680 | 44 | 350 | 1080 | 380 | ±7.0 | 30′ | 2.0 | 1350 |
| 25 | 250,000,000 | 1,250 | 225–340 | 745 | 44 | 350 | 1100 | 400 | ±8.0 | 30′ | 2.0 | 1580 |
| 26 | 315,000,000 | 1,200 | 250–365 | 785 | 50 | 350 | 1120 | 420 | ±8.4 | 30′ | 2.0 | 1650 |
| 27 | 400,000,000 | 1,150 | 270–380 | 830 | 50 | 380 | 1200 | 440 | ±9.0 | 30′ | 2.0 | 1950 |
| 28 | 500,000,000 | 1,100 | 290–400 | 875 | 50 | 400 | 1250 | 450 | ±9.6 | 20′ | 2.5 | 2200 |
| 29 | 630,000,000 | 1,000 | 320–425 | 935 | 60 | 400 | 1280 | 480 | ±10.0 | 20′ | 2.5 | 2300 |
| 30 | 800,000,000 | 930 | 340–440 | 1030 | 60 | 440 | 1380 | 500 | ±10.4 | 20′ | 2.5 | 2600 |
| 31 | 1,000,000,000 | 880 | 380–460 | 1080 | 66 | 460 | 1440 | 520 | ±11.0 | 20′ | 2.5 | 3500 |
| 32 | 1,250,000,000 | 820 | 400–500 | 1160 | 70 | 520 | 1620 | 580 | ±11.6 | 20′ | 2.5 | 4800 |
| 33 | 1,600,000,000 | 740 | 420–560 | 1290 | 82 | 570 | 1740 | 600 | ±12.4 | 20′ | 3.0 | 6100 |
| 34 | 2,000,000,000 | 680 | 460–600 | 1410 | 92 | 570 | 1740 | 600 | ±13.0 | 20′ | 3.0 | 7600 |
| 35 | 2,500,000,000 | 620 | 480–650 | 1530 | 105 | 610 | 1900 | 700 | ±13.6 | 20′ | 3.0 | 8600 |
| 36 | 3,020,000,000 | 570 | 500–710 | 1670 | 115 | 730 | 2210 | 750 | ±14.4 | 20′ | 3.0 | 11000 |
| 37 | 4,050,000,000 | 520 | 600–780 | 1830 | 125 | 800 | 2450 | 850 | ±15.0 | 20′ | 3.0 | 14700 |
| 38 | 5,300,000,000 | 480 | 650–860 | 2000 | 130 | 800 | 2500 | 900 | ±15.6 | 20′ | 3.0 | 21000 |
| 39 | 6,600,000,000 | 430 | 700–945 | 2200 | 140 | 960 | 2920 | 1000 | ±16.0 | 20′ | 3.0 | 26700 |
| 40 | 8,100,000,000 | 400 | 800–1030 | 2400 | 140 | 960 | 2920 | 1000 | ±16.4 | 20′ | 3.0 | 32000 |
| Symptom | Likely Cause | Action |
|---|---|---|
| High 1× vibration | Radial misalignment exceeding SJM limit; unbalance | Re-align; check coupling balance |
| High 2× vibration | Angular misalignment; damaged diaphragm | Check angular alignment; inspect both packs |
| Diaphragm crack at bolt hole | Bolt under-torqued (micro-slip) or over-torqued (fatigue) | Replace pack; verify bolt torque with calibrated wrench |
| Spacer contact noise | Misalignment causing spacer eccentricity | Re-align; check spacer running clearance |
Shaft fit, alignment and assembly checks
Keep flange faces, pilot surfaces and diaphragm packs clean. Align shafts before tightening the membrane fasteners and use the specified tightening sequence so clamp load is distributed evenly. Avoid bending, scratching or prying against the thin flexible elements. On spacer or intermediate-shaft versions, verify the assembled distance between shaft ends and check rotor balance for the intended operating speed.
Measure the actual shaft diameters and keyways before machining or confirming a finished bore. A drawing should identify shaft tolerances, key dimensions, required hub position and any shoulder, locknut or axial-retention feature. Alignment readings should be taken after the machine is in its normal installed condition because base distortion, pipe strain, belt pull or thermal growth can move the shaft centers after an initial bench alignment.
After assembly, turn the drive through at least one full revolution by hand where practical. Check for interference with guards, brake hardware and adjacent structures, then verify fastener security. On equipment that changes temperature significantly between start-up and steady operation, compare cold and hot alignment expectations before setting final offsets.
Operating behavior and service planning
No grease change is required, but visual and vibration monitoring remain important. Inspect for diaphragm cracking, fretting around bolt holes, loose fasteners, corrosion and unusual shaft movement. If a pack is replaced, investigate the root cause—commonly overload, excessive misalignment, incorrect bolt preload or an operating condition near a lateral critical speed.
A coupling should not be used as a permanent correction for poor machine alignment. If vibration, temperature or noise changes after commissioning, compare the current condition with the initial baseline. Check connected bearings and shafts at the same time, because many coupling symptoms originate from looseness, soft foot, imbalance or movement elsewhere in the drivetrain.
For planned maintenance, record the installed model, actual bore sizes, fastener details, lubricant or flexible-element grade where applicable, and the measured alignment at return to service. That information makes later inspection more useful and helps distinguish normal wear from a change in machine condition.
Information to include with an RFQ or drawing review
- Required model or the closest model already identified from the specification data.
- Driving and driven shaft diameters, tolerances, keyways and available engagement length.
- Continuous torque, peak torque, starts per hour and whether the drive reverses.
- Normal and maximum rotational speed.
- Expected angular, axial and parallel movement during operation.
- Required overall length, shaft separation, flange or brake dimensions and surrounding clearance.
- Operating temperature, contamination, washdown, corrosion or other environmental conditions.
- Quantity, drawing revision and any material, coating, balance or inspection requirement.
Frequently asked engineering questions
Can I select this coupling only from the motor power?
No. Motor power is only a starting point. The selection should use actual torque, service factor, peak load, speed and the driven-machine characteristics.
Which dimension should be confirmed before ordering?
Confirm the shaft interface first, then the overall installation envelope. Bore, key or locking method, hub length, pilot or flange details and available removal clearance all affect whether a listed model will fit.
How much misalignment should be allowed in normal service?
Use the model-specific limit as a maximum capability, not as the target installation condition. Better initial alignment usually reduces cyclic load, heat and wear in both the coupling and connected bearings.
What information is needed for a custom bore or connection?
Provide a dimensioned shaft drawing or at minimum the shaft diameter and tolerance, keyway, engagement length, shoulder or axial-retention details and required hub position.
Should the coupling be inspected after commissioning?
Yes. A short follow-up inspection after the machine has run under real load can reveal fastener settlement, lubricant leakage, unexpected movement or alignment change before these develop into a larger problem.
How should I use the specification blocks on this page?
Treat the listed values as the model reference. Select a candidate from torque and speed, then verify every geometric field that affects your installation before issuing the final order drawing.
Applications
Precision rotating equipment
Used where torsional stiffness and controlled alignment are important to drivetrain behavior.
Pumps & compressors
Applicable to rotating machinery where clean, lubrication-free coupling elements are preferred.
High-speed machinery
Considered when balance, speed, shaft fit and alignment are verified for the selected configuration.
Test & process systems
Suitable for engineered drivetrains that require repeatable torque transmission and documented installation geometry.
Typical duties include pumps, compressors, turbines, test equipment, high-speed machinery, precision industrial drives and long-span shaft connections. The correct configuration depends on torque, speed, misalignment mode, shaft spacing and balance requirements.
The same coupling family can behave very differently in a smooth continuous drive and in a reversing, impact-loaded or frequently started drive. For that reason, application name alone is not enough for selection. Supply the operating torque, peak load, speed, shaft dimensions, expected movement, ambient conditions and required service access so the configuration can be checked against the complete duty.