79C1 – Textron Aviation OEM Fuel Sump Drain Valve (Saf-Air F391-S)
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Overview
The 79C1 is the genuine Textron Aviation Original Equipment Manufacturer (OEM) part number for the industry-standard Saf-Air F391-S fuel sump drain valve. This is a flight-critical component installed in fuel tanks, gascolators, and low points in an aircraft's fuel system. Its primary function is to provide a secure and reliable means for pilots and mechanics to drain fuel samples for pre-flight inspection of water and sediment contamination, and for draining tanks for maintenance.
This valve features a time-tested, spring-loaded poppet design. The valve is opened by depressing the central stem with a fuel sampler tool and automatically springs shut to provide a positive seal when the tool is removed. It is manufactured from corrosion-resistant materials, including a brass body and a Viton® (fluorocarbon) O-ring seal, to ensure long-term, leak-free performance when exposed to aviation fuels.
Key Features
Genuine Textron Aviation OEM Part: Guarantees the part is the factory-specified and fully certified component for Textron aircraft, ensuring quality and traceability.
Corresponds to Saf-Air F391-S: The OEM part number for the proven, industry-standard Saf-Air fuel drain valve design.
Spring-Loaded Poppet Design: Provides a simple, reliable, and positive sealing mechanism. The valve is normally closed and is sealed by a combination of spring pressure and fuel pressure.
Viton® (Fluorocarbon) Seal: The O-ring seal is made from Viton®, a high-performance elastomer specified for its excellent chemical resistance to aviation gasoline (Avgas), jet fuel, and their additives.
Corrosion-Resistant Brass Body: The valve body is machined from a solid brass alloy for long-term durability and resistance to corrosion from fuel and entrained water.
Standard 1/8" NPT Thread: Features a standard 1/8-27 National Pipe Taper thread for installation in a wide range of fuel tanks and system components.
Technical Specifications
Part Number: 79C1
Underlying Part Number: Saf-Air F391-S
Component Type: Fuel Sump Drain Valve
OEM Authority: Textron Aviation
Underlying Manufacturer: Saf-Air Products, Inc.
Body Material: Brass
Seal Material: Viton® (Fluorocarbon)
Thread Size: 1/8-27 NPT
Actuation: Push-to-Open, Spring-Return to Close
Aircraft Compatibility
The 79C1 is one of the most widely used fuel drain valves in general aviation, specified as the standard part on a vast fleet of Textron Aviation aircraft.
Primary Textron Aviation Platforms:
Cessna Piston Aircraft (150, 152, 172, 182, 206, 210, etc.)
Cessna Piston Twins (310, 337, 340, 400-series)
General Aviation Usage: Also used by numerous other aircraft manufacturers for fuel system drain applications.
Note: Verification of applicability is the absolute responsibility of the installer. The aircraft's current Illustrated Parts Catalog (IPC) for its specific serial number is the final authority for confirming part number eligibility.
Applications
Sole Application: To provide a manually actuated drain point in an aircraft fuel system for:
Pre-flight fuel sampling to check for water and sediment.
Draining fuel tanks and gascolators for maintenance.
Draining low points in the fuel plumbing.
Why Choose 79C1?
Fuel system integrity is paramount to flight safety. A leaking fuel drain valve is a significant and constant fire hazard, as well as a source of fuel loss. The genuine OEM 79C1 valve, representing the proven Saf-Air F391-S design, is the only part guaranteed to be manufactured with the correct materials—especially the fuel-impervious Viton® seal—and the precise spring tension and dimensions required for a reliable, positive seal, flight after flight. Using a non-certified or imitation valve introduces an unacceptable risk of fuel system leakage.
The reliability of the 79C1 (Saf-Air F391-S) drain valve is a function of its simple and robust engineering. The heart of the valve is a poppet that seals against a precision-machined seat, with the primary sealing interface being a Viton® (FKM) O-ring. Viton®, a fluorocarbon elastomer, is specified for this application due to its exceptional chemical resistance and low swell characteristics when exposed to the aromatic hydrocarbons present in aviation gasoline. A standard Nitrile (Buna-N) O-ring would swell and soften over time, leading to a leaking or stuck valve. The poppet is held in the closed position by a stainless steel spring, which provides the initial sealing force. This force is augmented by the static head pressure of the fuel in the tank acting on the face of the poppet, creating a self-energizing seal that becomes tighter as the fuel level increases. This dual-action sealing provides a high degree of reliability against leaks.
Note: This is a flight-critical fuel system component. Installation must be performed by a certified A&P mechanic. A fuel-resistant thread sealant appropriate for NPT threads must be used on the valve body during installation. The valve should be torqued to the manufacturer's specification. After installation, and after the sealant has cured, the fuel system must be filled and the valve and surrounding area must be thoroughly inspected for any signs of leakage before the aircraft is returned to service.
Documentation
Installation procedures are detailed in the applicable aircraft maintenance manual. Additional product details are available from the manufacturer, Saf-Air Products, Inc.