Maintain turbine bearings by checking them every week for heat, noise, play and coast-down time, lubricating to a written interval, and keeping spray and grit out of the housing, because a dry metal bearing can seize within an hour of heavy use and a gritty one wears quickly. Time how long the runner spins after the gate closes: a coast time that has halved means the bearing drag has roughly doubled, and the water should be shut off and the bearing opened before it fails.
Part of Micro-Hydro Turbine
Bearings hold the turbine and generator shafts in place while they spin; in a powerhouse they work in spray, grit and vibration, and the carrier tells the operator to check them weekly.
Bearings Fail From Four Causes
- No lubricant. The Lubrication page says a dry wooden axle can char within minutes and a dry metal bearing can seize within an hour.
- Water and grit. Spray from a nozzle or tailrace carries sand into the housing, where it wears the surfaces.
- Side load. A belt pulls on the shaft ends (Generator Coupling (Belt vs Direct)); an over-tight belt shortens bearing life.
- Misalignment. Shafts not in line load one side of the bearing.
Choose The Bearing By Shaft Speed
The Bearings and Bushings page puts bushings at slow speeds under 500 RPM and heavy loads, and ball bearings at higher speeds and where low friction matters, such as generators. For the plants in this series:
- An overshot wheel at 5-15 RPM: bronze or hardwood bushings.
- A crossflow at about 309 RPM: bushings or pillow-block ball bearings, either works.
- A Pelton at about 568 RPM and the generator at 1,500 RPM: ball bearings.
Bearings and Shafts covers plain bearing fits.
Method: The Weekly Check
Step 1: Look and listen while running. A steady hum is normal. Grinding, squeal or a changing note is not.
Step 2: Feel the housing. Put the back of your hand on it. If you cannot keep it there for about 5 seconds, it is above roughly 60 °C (a recalled figure for the limit of a held hand). Tallow melts at 40 to 50 °C (Lubrication), so a bearing at that temperature has already pushed its grease out; wax in the mix raises the melting point.
Step 3: Time the coast-down. Shut the turbine gate, start a stopwatch, and stop it when the shaft stops. Write the time in the log. For constant friction torque the coast time is t = J × ω ÷ T, where J is the moment of inertia of the rotating parts, ω the speed and T the friction torque, so the time is inversely proportional to the drag. Halving the coast time from 90 s to 45 s means the drag has about doubled. Real friction is not perfectly constant, so treat the ratio as a warning, not a measurement.
Step 4: Stop the water and check play. With the machine at rest and the gates shut, grip the shaft close to the bearing and try to rock it. Any movement beyond a hair’s breadth means wear.
Step 5: Lubricate to the written interval, wiping the old grease out of the housing if it is gritty.
Step 6: Log it: date, temperature by hand, coast time, play, what you added.
Worked Example: Why A Little Drag Matters
Friction torque × angular speed is the power lost. The numbers below are illustrative.
- A Pelton at 568 RPM turns at 59.5 rad/s. A bearing drag of 0.2 N·m wastes 0.2 × 59.5 = 12 W.
- Worn, the drag rises to 0.5 N·m: 0.5 × 59.5 = 30 W.
- Against 750 W at the shaft (Pelton Wheel (High Head)), that is a loss of 1.6% rising to 4%. The power loss is small. The warning is the heat: 30 W concentrated in a small housing turns the grease to oil, then to a dry bearing.
Diagnosing A Bearing
| Symptom | Likely cause | Action |
|---|---|---|
| Hot housing, quiet | too little lubricant or too tight a belt | add lubricant; ease the belt |
| Grinding that rises with speed | grit or damaged surface | strip, clean, replace |
| Shaft moves when rocked | worn bushing or bearing | replace before the shaft wears |
| Coast time shorter than the log | rising drag | find which bearing by spinning each by hand |
| Rust or water in the grease | failed seal or spray | add a splash guard; move the bearing |
Common Mistakes
- Over-greasing — it churns, heats and pushes into places it should not.
- Greasing a running bearing near a belt — use a remote fitting or stop the machine.
- Replacing one bearing of a pair and leaving the worn one.
Safety
Rotating shafts take loose clothing
Never oil, feel or inspect a bearing while the shaft is turning near a belt or coupling. Shut the gate, wait for the shaft to stop, and confirm by eye. The stop is the turbine gate; the coast time in the log tells you how long to wait.
What’s Next
- Learn next: Debris & Ice Management for the other daily job
- Combine with: Maintenance & Troubleshooting for the full schedule