Description
The fluid coupling — also known as a hydrodynamic coupling or hydraulic fluid drive — transmits torque from driver to driven shaft entirely through the acceleration and deceleration of oil inside a sealed housing. No mechanical contact exists in the torque path during normal operation. The starting characteristic is controlled soft-start; the running characteristic is full motor power transmission; the overload characteristic is automatic torque limitation through controlled slip. The YOX series covers constant-fill industrial fluid couplings from 0.6 kW to 550 kW across applications including conveyor drives, crushers, fans, and diesel engine connections.
YOX Series Fluid Coupling Power Specifications
The YOX series is sized by working diameter and motor power at the rated motor speed. The published power tables cross-reference working diameter against the three common motor speeds (1500 rpm, 1000 rpm, 750 rpm) and the corresponding power transmission envelope. Higher motor speeds produce higher power transmission at the same working diameter because the centrifugal action on the oil is the torque-transmission mechanism, and oil acceleration rises with the square of motor speed.
| Model | Power @ 1500 rpm (kW) | Power @ 1000 rpm (kW) | Power @ 750 rpm (kW) | Oil Fill (L) | Weight (kg) |
|---|---|---|---|---|---|
| YOX-190 | 0.6 – 1.1 | — | — | 0.4 – 0.8 | 8 |
| YOX-250 | 2.5 – 5.0 | 0.7 – 1.5 | — | 1.1 – 2.2 | 15 |
| YOX-320 | 7.5 – 15 | 2.7 – 5.0 | 1.1 – 2.2 | 2.5 – 5.0 | 28 |
| YOX-400 | 22 – 45 | 7.5 – 15 | 3.0 – 6.0 | 4.6 – 9.0 | 65 |
| YOX-450 | 40 – 75 | 14 – 28 | 6.1 – 11 | 6.5 – 13 | 70 |
| YOX-500 | 75 – 132 | 26 – 50 | 10 – 19 | 10 – 19 | 133 |
| YOX-560 | 132 – 250 | 45 – 90 | 19 – 30 | 14 – 27 | 158 |
| YOX-600 | 200 – 375 | 60 – 120 | 25 – 50 | 24 – 40 | 170 |
| YOX-710 | — | 150 – 280 | 60 – 115 | 37 – 60 | 310 |
| YOX-1000 | — | — | 270 – 550 | 70 – 140 | 510 |
Oil fill quantity is the primary tuning parameter for a constant-fill fluid coupling. Higher fill produces lower slip at rated load and higher power transmission for a given working diameter; lower fill produces higher slip and more pronounced soft-start behaviour. Standard factory fill is the centre value of the published range — adjust upward for steady-state efficiency applications and downward for high-shock applications where additional slip protection is required.
YOX Series Fluid Coupling – constant-fill hydrodynamic coupling for soft-start and overload protection. Ever Power Flange Couplings Australia Ltd.
How the YOX Fluid Coupling Transmits Torque
Inside the sealed housing of the YOX fluid coupling, two bowl-shaped impellers face each other across an oil-filled annulus. The pump impeller is fixed to the input shaft from the motor; the turbine impeller is fixed to the output shaft to the driven equipment. Both impellers carry radial blades inside the bowl curvature. The housing is partially filled with industrial turbine oil to the specified fill level for the working diameter and the application.
When the motor starts, the pump impeller spins up. Oil inside the pump bowl is flung outward by centrifugal force; the radial blades direct the oil flow circumferentially as it crosses the gap between the impellers. This high-velocity oil strikes the radial blades of the turbine impeller, imparting torque to the turbine and the connected output shaft. Once the turbine reaches roughly 95% of the input speed, the oil circulation establishes a steady-state pattern and the coupling transmits the full motor power to the driven equipment.
Why Hydrodynamic Power Transmission Matters
The defining characteristic of the fluid coupling is that no mechanical contact exists in the torque path during normal operation. The motor is connected to the driven equipment only through the oil mass — and the oil yields under shock load. During motor starting, the motor accelerates freely while the load follows along progressively as the oil circulation builds up; starting current drops from the typical 6–8× FLC of a direct-coupled drive to 2–3× FLC on the fluid coupling. During overloads, the slip between pump and turbine rises automatically, limiting transmitted torque and protecting the motor from stall conditions.
Construction and Material Specification
The YOX housing is a precision cast iron casting machined to dimensional tolerance — chosen for the combination of vibration damping, manufacturing economy, and thermal stability under the operating temperature range. Pump and turbine impellers are cast aluminium for low rotational inertia, with the radial blades produced as part of the impeller casting and lightly machined where the bowl curvature interfaces with the input and output shaft connections. Shaft seals are lip-type seals running on hardened shaft sleeves.
The fusible plug is a critical safety component on every YOX coupling. Threaded into the housing wall at a defined radial position, the fusible plug carries a low-melting-point alloy core that liquefies at 120°C — the warning temperature for thermal runaway during prolonged overload. When the core melts, the oil discharges from the housing through the plug bore, isolating the coupling from continued power transmission. This passive protection prevents catastrophic housing failure and contains the overload event without operator intervention.
Engineering Features of the YOX Fluid Coupling
Motor accelerates freely against the unloaded pump impeller; load follows progressively as oil circulation builds. Starting current drops from 6–8× FLC direct-coupled to 2–3× FLC on the fluid coupling. Extends motor service life through reduced thermal cycling.
Slip rises automatically under overload conditions, limiting transmitted torque and protecting the motor and gearbox downstream. Passive protection without sensors, relays, or programmed control system intervention.
Oil mass between pump and turbine acts as a torsional damper, absorbing the firing pulsations of diesel engine drives and the cyclic torque variations of reciprocating compressors. Reduces fatigue loading on downstream gearbox and shafting.
Two or more motors driving a common load through fluid couplings automatically share the load equally — the coupling slip rises on whichever motor is delivering more than its share, redirecting load to the other motors. Eliminates the load-balancing problem of multi-motor conveyor drives.
Fusible plug melts at 120°C, discharging oil and isolating the coupling from continued power transmission. Prevents catastrophic housing failure during prolonged overload events. Replaceable as a stock spare item.
Torque transmitted through oil mass with no mechanical contact during normal operation. Shaft seals and bearings are the only wear points; coupling service life equals the seal and bearing service life — typically 5 to 10 years.
YOX fluid coupling installation – soft-start and overload protection for industrial conveyor and crusher drives across Australian mining operations.
Application Field for the YOX Fluid Coupling
Belt conveyor drives are the largest single application class for the YOX series across Australian heavy industry. Loaded belt conveyors require very high starting torque to overcome static friction and accelerate the loaded belt mass; direct-coupled motor starting produces severe belt slip on the head pulley, peak shaft loading on the gearbox, and starting-current excursions that disturb the local electrical supply. The fluid coupling solves all three problems through the controlled soft-start characteristic — making the YOX coupling the standard power transmission coupling for new conveyor installations.
Crusher, Fan, and Compressor Drive Applications
Jaw crushers, cone crushers, and impact crushers experience violent torque spikes when the crushing chamber encounters an unbreakable rock or a foreign object. The YOX coupling absorbs the spike through controlled slip, protecting the motor and the downstream gearbox from peak-torque damage. Centrifugal fans and forced-draft blowers benefit from the soft-start characteristic on equipment with high rotational inertia. Diesel engine drives use the YOXz integrated elastic variant — the fluid coupling combined with an elastomeric flexible coupling — to handle both starting characteristics and engine firing pulse vibration in a single assembly.
Selecting the Correct YOX Size and Oil Fill
YOX sizing starts with motor nameplate power at the rated motor speed. The published power table identifies the YOX working diameter range that supports the required motor power. Within that working diameter range, oil fill quantity is then selected against the application service factor — higher fill for steady-state efficiency applications and lower fill for high-starting-torque applications. Provide motor nameplate power, motor speed, application type, and ambient temperature range to our Sydney engineering team for confirmed size and fill recommendation.
Oil viscosity grade selection follows the ambient temperature range. ISO VG46 turbine oil or anti-wear hydraulic oil is the standard fill for typical Australian ambient temperatures (-5°C to +40°C). Cold-ambient installations use ISO VG32 to maintain low-temperature flow characteristics; hot-ambient installations and high-power continuous-duty applications use ISO VG68 to preserve the lubricant film at elevated operating temperature. Never substitute engine oil, gear oil, or transmission fluid — these lubricants contain sulphur additives that attack the lip seal compounds.
Installation and Commissioning Workflow
YOX installation follows the same precision-alignment workflow as any flanged industrial coupling, with the additional steps of correct oil fill and fusible plug verification before commissioning. The five-step workflow below covers initial installation; the same workflow applies for oil change service at scheduled maintenance intervals or after fusible plug replacement events.
Mount the YOX coupling on the motor shaft and the driven equipment shaft per the documented engagement length and orientation. Bring driver and driven equipment to rough alignment with straight edge before precision laser alignment.
Align angular and parallel offset to within published envelope — typically 0.3° angular and 0.2 mm parallel offset. The YOX hub is not a torsional damper and does not compensate misalignment beyond the published values; field alignment quality directly determines bearing and seal service life.
Confirm fusible plug is installed and torqued to specification. Fill the housing with the specified oil grade and quantity through the fill port. Verify oil level through the sight glass or dip-stick; correct level is mid-band on the visible range with the coupling stationary and at ambient temperature.
Bump-start the drive briefly to verify rotation direction and confirm normal start behaviour. Run for 30 minutes at progressive load monitoring oil temperature carefully; normal operating temperature is ambient plus 30 to 50°C in standard duty. Recheck oil level after commissioning run.
At 250 operating hours or 1 month service, drain the oil and inspect for contamination. Refill with fresh oil if any contamination indicators are present (water, metal flakes, viscosity change). Confirm shaft seal integrity and fusible plug condition. Document the inspection in the equipment maintenance record.
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Maintenance Schedule and Fusible Plug Response
Routine YOX maintenance is oil change at scheduled intervals — typically every 8000 operating hours or annually, whichever comes first. Oil is drained through the bottom plug and refilled through the fill port; the housing does not require disassembly for routine oil service. Shaft seals are inspected annually and replaced every 3 to 5 years depending on duty severity. Fusible plug condition is verified at each oil change.
If the fusible plug activates during service, the response procedure is: shut down the drive, allow housing to cool, replace the fusible plug with a fresh stock spare, refill with the correct oil grade and quantity, and investigate the root cause of the overload event before restarting. Common fusible plug activation causes include sustained overload on a sticking driven machine, loss of cooling air flow around the coupling housing, and ambient temperature exceeding the design envelope. Address the root cause; never simply replace the plug and restart without investigation.
Why Choose Ever Power Australia
Ever Power Flange Couplings Australia Ltd. supplies the complete YOX fluid coupling range from our Sydney warehouse — YOX-190 through YOX-1000 for industrial conveyor, crusher, fan, and diesel engine drives across Australia. Fusible plugs, replacement seals, and bearing kits are stocked separately for field service. The ISO 9001 quality management system ensures consistent housing dimensions, impeller balance, and seal quality across the range. Voith fluid coupling and Fluidomat cross-reference work is provided directly from our Condell Park technical office.
Ever Power manufacturing facility — ISO 9001 certified, 12,000 m², 108 dedicated coupling machines, 20+ years of production experience.
Every order placed with our Sydney team is backed by full material traceability, dimensional inspection certificates on request, and direct access to the engineers who specified, machined, and packed your coupling. We do not subcontract technical support — when you phone +61 2 9708 3322 during NSW business hours, you reach the people who actually know the product.
Frequently Asked Questions
Quick answers from our Sydney technical team. Contact us for application-specific guidance.
1. How much does the fluid coupling reduce motor starting current? +
2. What happens if the fusible plug activates during operation? +
3. Can two motors share a load through fluid couplings? +
4. What oil should I use in the YOX fluid coupling? +
5. Is the YOX a direct equivalent for Voith or Fluidomat fluid couplings? +
Request a Quote — Sydney NSW Stock
Tell us your motor power, shaft diameter, and operating environment. Our New South Wales coupling team confirms availability and pricing within one business day, with same-day dispatch on standard sizes from Condell Park.
Ever Power Flange Couplings Australia Ltd. · 27 Harley Crescent, Condell Park NSW 2200 · [email protected]
