A Kaplan turbine adjusts runner blade pitch as water flow changes. Inside the rotating runner hub, bushings support the blade trunnions and, in some designs, parts of the blade adjustment mechanism. There is no single standard-size “Kaplan bushing” that fits every runner.
For an overhaul, the first task is to identify the worn position. The mating surfaces, lubrication arrangement, and required finished dimensions must then be confirmed before replacement parts are made. These checks help the plant or overhaul contractor prepare an accurate manufacturing request.
Where Are the Bushings in a Kaplan Runner Hub?
A blade trunnion is the shaft-like part around which a runner blade changes pitch. Depending on the hub design, an inner and an outer trunnion bushing support it. Drawings may also call these runner blade bearings or blade pivot bushings. The inner and outer parts should be identified separately because their dimensions and lubrication details may differ.
The pitch adjustment mechanism can contain link pin bushings at its pivot points. Some designs also use upper and lower piston rod bushings to guide the rod that moves the linkage. These parts serve different functions from the blade trunnion bushings. Their presence and exact locations depend on the turbine design.
A turbine shaft guide bearing supports the main shaft at another position. A wicket gate bushing belongs to the water-control mechanism outside the runner hub. Naming the component simply “hydro turbine bushing” leaves too much room for error.
Before requesting a quote, record the turbine unit, blade position, part name, and OEM part number where available. Our hydropower components page shows the broader range of custom bearing parts that may be included in a refurbishment project.
What Should an Overhaul Inspection Look For?
Increased blade droop, irregular pitch movement, or changing conditions around a trunnion seal can justify closer inspection. None of these observations proves that a bushing alone has failed. Loads, bearing deformation, mating surfaces, and seal condition can all affect what the maintenance team sees. Oil leakage calls for a check of the sealing system and hub, rather than an automatic bushing order.
During the planned overhaul, identify removed parts before they are mixed together. Record scoring, uneven or oval wear, damaged edges, corrosion, and the condition of oil grooves. Photograph the wear pattern and note the installed orientation. Comparing equivalent positions across the runner can help the site team decide where further measurements are needed.
Measure the trunnion journal and hub bore, as well as the removed bushing. The inside diameter of a worn bushing is not necessarily its original specified diameter. A damaged journal, distorted housing bore, or loss of concentricity may also affect the required replacement dimensions.
If the overhaul plan includes repairing a journal or machining a hub bore, confirm the resulting dimensions before finalizing the bushing drawing. Running clearance and reuse limits must follow the unit’s approved specifications and the responsible engineer’s assessment. A clearance reported for another Kaplan turbine is not a universal standard.
What Must Be Specified for Replacement Bushings?
A manufacturing package should identify each part by its location, drawing number, and revision. Provide the required material, inside and outside diameters, length, tolerances, grooves, holes, quantity, and inspection requirements. State whether the bushing must leave the factory with a finished bore or with machining allowance for final sizing after installation.
Material and lubrication must be specified together. An oil-lubricated bronze hub and an oil-free hub can require different bearing systems and mating surfaces. A Pacific Northwest National Laboratory study compared existing grooved bronze bushings at one dam with candidate self-lubricating alternatives. That project does not establish a universal replacement material.
If an approved design calls for graphite-plugged bronze, our custom oilless bushings may be relevant. A proposed change from the original material or lubrication system needs approval from the equipment designer; matching the old part’s dimensions is not sufficient.
Include available journal and housing measurements, the lubrication method, and details of any planned repairs. For several part numbers, provide a list showing the drawing revision and quantity for each. Mark unverified dimensions clearly. Unusual profiles or related components can be reviewed as custom bronze parts against their drawings.
Finally, agree which dimensions will be inspected before shipment and which will be established by the overhaul contractor after installation. That distinction makes the manufacturing scope and site handoff clear.
Send Your Kaplan Runner Hub Bushing Drawings for Review
JEDBUSHING manufactures custom bronze components for OEM and hydropower replacement orders. Through our contact page, send the drawings or available sample information, part identification, material requirements, quantities, and inspection needs. Include the outage schedule and note any planned hub-bore or trunnion repairs.
We will review the manufacturing requirements and identify missing information before quoting. The plant or its appointed overhaul contractor handles equipment diagnosis, disassembly, installation, and any on-site line boring.
FAQ
Can the same bushing drawing be used for another Kaplan unit of the same model?
Check the drawing revision, part position, and actual mating dimensions first. Units of the same model may differ because of design revisions or previous repairs.
Must every blade position be replaced during one outage?
Not automatically. The owner and overhaul engineer should compare inspection results with the maintenance plan before deciding which positions need replacements or spare parts.
Can JED quote if the original OEM drawing is missing?
Send photos, part markings, available measurements, and the trunnion and housing dimensions. We can review the information, but a severely worn sample cannot establish the original clearance by itself. Critical dimensions must be verified before manufacture.
Does JED perform on-site line boring or turbine repair?
No. JED manufactures parts to the agreed drawing and inspection requirements. The plant or its overhaul contractor is responsible for field machining, assembly, and acceptance checks.