3112859-01 – Pratt & Whitney OEM Retaining Seal Plate for PT6 Engines 🚀
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Overview
The Pratt & Whitney (P&WC) 3112859-01 Retaining Seal Plate is a high-precision Original Equipment Manufacturer (OEM) component critical to maintaining the internal integrity of the PT6A turboprop engine lubrication and gas path systems. Specifically, this plate is a meticulously machined element used within the engine's reduction gearbox or accessory gearbox section where it secures and positions a dynamic seal element, such as a carbon seal or labyrinth seal, against a rotating shaft. Its primary function is to provide a rigid, flat, and precisely dimensioned mounting surface that ensures the optimal running clearance and face pressure of the seal, which is non-negotiable for preventing catastrophic oil or air leakage between different pressure zones inside the engine.
The reliability of the 3112859-01 is flight-critical. Failure to maintain the seal integrity in this area can lead to excessive oil consumption, oil contamination of the air stream, or a dangerous drop in local air pressure, which could compromise the engine's performance or lubrication systems. As a certified OEM part, it ensures the tight tolerances, material purity, and surface finish required for the sensitive, high-speed environment of the PT6A engine.
Key Features
High-Precision Machining: Manufactured to extremely tight tolerances (often in the range of $\pm 0.0005$ inches) to ensure the flatness and parallelism required for effective seal seating and function.
Seal Face Integrity: Provides the crucial static platform against which the dynamic seal element operates, dictating the stability and life of the seal.
High-Strength, Thermal Stability: Composed of an alloy specifically selected to maintain dimensional integrity under the engine's severe operating temperatures and dynamic loads.
Corrosion Resistance: Material and finish are selected to resist chemical degradation from hot lubricating oil and high-temperature air or combustion gases.
Precise Positioning: Acts as a datum for locating the complex sealing system components within the gearbox, directly influencing internal clearances and pressure boundaries.
Technical Specifications
Part Number: 3112859-01
Component Type: Retaining Seal Plate / Seal Housing Component
OEM Manufacturer: Pratt & Whitney Canada (P&WC)
Engine Applicability: Used across various models of the PT6A Turboprop Engine Family (e.g., PT6A-42, -60A, -135A).
Material: Must be confirmed by OEM documentation. Typically a high-strength Nickel-based Superalloy (such as Inconel 718 or a specialized CRES variant) for thermal and corrosion stability, or a high-strength aluminum alloy if located in the cooler reduction gearbox section.
Finish: Precision ground and polished surface, often heat-treated and/or coated for wear resistance.
Dimensional Data: Specific inner diameter, outer diameter, and depth are determined by the particular seal assembly it supports.
Certification: Original Production Certificate (PC) Approved by the applicable regulatory bodies.
Aircraft Compatibility
Primary Models: Found in aircraft utilizing the applicable PT6A engine variants, including:
Beechcraft King Air Series (e.g., B200, 350)
Cessna Caravans (e.g., C208B)
Pilatus PC-12 Series
De Havilland Canada Twin Otter
System Integration: An internal part of the Gas Generator or Reduction Gearbox Assemblies within the PT6A engine.
Verification Note: The Pratt & Whitney Illustrated Parts Catalog (IPC) and Engine Maintenance Manual (EMM) for the specific PT6A engine model are the definitive and final authority for part applicability.
Applications Section
The 3112859-01 plate is crucial to the reliable functioning of several core engine systems:
Lubrication System Integrity: Securing oil seals around rotating shafts to ensure pressurized oil remains within the bearing cavities and gear trains.
Compressor/Turbine Sealing: Providing mechanical backing for air seals that maintain the pressure differential necessary for efficient gas flow (less common application, but possible depending on the dash number).
Internal Component Alignment: Maintaining the necessary axial and radial clearances for high-speed rotating elements.
Why Choose the 3112859-01 OEM Retaining Seal Plate?
The Pratt & Whitney 3112859-01 operates in an environment defined by high rotational velocity, thermal stress, and oil pressure. The function of the seal it retains is directly dependent on the plate's absolute flatness, surface roughness, and dimensional accuracy. Using non-OEM parts or improperly repaired plates carries the extreme risk of seal blowout or premature wear. A seal failure in the PT6A can lead to oil starvation of critical bearings or, potentially, the ingestion of hot air and contaminants into the oil system. This certified OEM plate guarantees the material's certified creep resistance and thermal stability, ensuring the seal maintains its critical clearance margin throughout the engine's operational envelope.
This Retaining Seal Plate is functionally part of a hydrodynamic or face seal system. The plate itself provides the stationary reactionary surface that controls the gap (or axial preload) relative to the rotating seal face. In carbon face seals, the successful operation relies on the maintenance of an extremely thin hydrodynamic film of oil or air between the stationary plate surface and the rotating carbon ring.1 Any deviation in the plate's flatness or surface finish due to thermal distortion or wear can destroy this film, leading to immediate dry running, thermal runaway, and rapid seal failure. The material's selection is optimized for low thermal expansion to minimize dimensional change across the vast temperature range encountered in a turboprop's power section, thus preserving the crucial seal clearance.
Note: The 3112859-01 Retaining Seal Plate is a flight-critical engine component with extremely tight dimensional requirements. Due to its direct interaction with high-speed dynamic seals, even microscopic surface damage or deviation from the certified flatness tolerance renders the part unserviceable. Inspection must include non-destructive testing (NDT) and precise dimensional verification per the Pratt & Whitney Overhaul Manual. This part is not field-repairable; only certified replacement or overhaul procedures are permitted. Installation must be performed and certified by a licensed A&P mechanic or engine specialist in strict accordance with the PT6A Engine Maintenance and Overhaul Manuals.
Documentation
No public-facing OEM or regulatory documentation was located for this specific part number. Consult the Pratt & Whitney Canada (P&WC) PT6A Engine Maintenance Manual (EMM) and Illustrated Parts Catalog (IPC) for the specific engine model to verify fitment and detailed installation procedures.