3/8 in. FNPT Brass Three-Way Valve | Moeller Marine Products 033312-10

Moeller 033312-10 Brass Three-Way Fuel Valve | 3/8" FNPT | Dual Tank to Single Engine | One Tank at a Time

The Moeller #033312-10 is a brass three-way fuel selector valve with 3/8" female NPT (FNPT) ports. Connects two permanent fuel tanks to a single engine, allowing the operator to select which tank feeds the engine from a single valve position. Designed to draw from one tank at a time only — not both simultaneously. All-brass construction for fuel compatibility and corrosion resistance in marine environments.

Part Details:

• Part Number: 033312-10 (Moeller Marine Products)
• SKU: MO-033312-10
• Manufacturer: Moeller Marine Products
• Type: Three-Way Fuel Selector Valve
• Port Size: 3/8 in. FNPT (female NPT)
• Material: Brass
• Configuration: 2 tank inlets, 1 engine outlet
• Operation: One tank at a time (not simultaneous draw)
• Condition: New

Additional Information

How the Three-Way Valve Works:

The Moeller 033312-10 has three 3/8" FNPT ports — two inlet ports (one from each tank) and one outlet port to the engine fuel system. Rotating the valve handle selects which tank feeds the engine. Only one inlet is open at any valve position; the other is closed. This prevents cross-tank siphoning and allows the operator to switch tanks without shutting down the engine, managing fuel balance across a dual-tank installation.

One Tank at a Time — Not a Blending Valve:

The 033312-10 draws from one tank at a time only. It is not designed to draw from both tanks simultaneously and should not be used in that configuration. Attempting to draw from both tanks at once by positioning the valve between detents can cause fuel starvation, air ingestion, or cross-tank siphoning depending on the installation. Use the valve as designed — select one tank, run it down to your desired level, then switch to the second tank.

3/8" FNPT — Thread Type and Fitting Compatibility:

All three ports are 3/8" female NPT (National Pipe Taper). NPT is a tapered thread standard that seals on the threads themselves with thread sealant — not a compression or flare fitting. Use fuel-compatible thread sealant (not Teflon tape alone) on all NPT fittings per ABYC standards for marine fuel systems. Confirm your fuel line fittings are 3/8" male NPT before purchasing.

Brass Construction — Fuel Compatibility:

Brass is compatible with gasoline, ethanol-blended fuel (E10), and diesel. The 033312-10 is appropriate for both gasoline and diesel dual-tank marine fuel systems. Confirm no downstream components in your fuel system restrict fuel type before installation.

Installation Notes:

• Mount the valve in an accessible location at or near the helm for easy tank switching during operation
• All three ports are 3/8" FNPT — use fuel-compatible thread sealant on all NPT connections
• Label the valve positions clearly (PORT TANK / STBD TANK or equivalent) after installation
• Confirm fuel line hose is rated for marine fuel use and sized for 3/8" NPT fittings
• Test for leaks at all three port connections before returning the vessel to service

Frequently Asked Questions

1. Can this valve draw from both tanks at the same time?
No — the 033312-10 draws from one tank at a time only. It is a selector valve, not a manifold. At any valve position, one tank inlet is open and the other is closed. Do not use this valve to attempt simultaneous dual-tank draw.

2. What thread type are the ports?
All three ports are 3/8" FNPT (female National Pipe Taper). Your fuel line fittings must be 3/8" male NPT. Use fuel-compatible thread sealant on all NPT connections per ABYC standards — do not rely on Teflon tape alone for fuel system NPT joints.

3. Is this valve compatible with ethanol-blended fuel?
Yes — brass is compatible with E10 ethanol-blended gasoline and diesel. The 033312-10 is suitable for both fuel types.

4. Where should this valve be mounted?
Mount the valve in an accessible location near the helm so the operator can switch tanks during operation without leaving the helm. Clearly label the valve positions for each tank after installation.

5. Does this valve have a shut-off (off) position?
Moeller's 033312-10 is a three-way selector valve — confirm whether an off position is included by checking the valve's position detents after installation. If a dedicated fuel shut-off is required for your installation, a separate inline shut-off valve should be installed upstream of the selector valve.