Fluid Line Sizes in RV Aircraft (4D, 6D, 8D)
The three fluid line sizes used across the RV series and where each is used
RV series aircraft use three fluid line sizes — 4D, 6D, and 8D — each assigned to specific systems: brake and vent lines, fuel lines, and oil cooler lines respectively. Thread sealant is required on NPT fittings but must never be applied to AN flare fittings.
What are the three fluid line sizes used in RV series aircraft?
Across the RV series there are only three sizes of fluid lines:
- 4D - brake lines and fuel tank vent lines.
- 6D - all fuel lines from the tanks to the fuel servo (or carburetor).
- 8D - oil cooler lines, to and from the oil cooler.
When should thread sealant be used on fittings?
Use thread sealant on NPT (national pipe thread) fittings only. Do not use thread sealant on AN flare fittings, and never use a torque wrench on NPT fittings.
- AN flare fittings — No thread sealant.
- NPT fittings — Thread sealant required; do not use a torque wrench.
Where can I find correct line, fitting, or routing information for my RV model?
For the correct line, fitting, or routing on your model, check the relevant section of your manual or contact Van's Builder Tech Support.
Source: Van's Builder Technical Support reference material.