Fluid Lines & Fittings
How should a flexible hose be installed with respect to length, and why?
Answer
Provide about 5 to 8 percent slack because the hose changes length when pressurized
Flexible hose contracts in length (and expands in diameter) when pressurized, so roughly 5 to 8 percent slack is provided; an over-tight installation would place the hose under tension and could pull loose or fail. Hose does change dimensions under pressure, and 25 percent is far more slack than needed, which invites chafing and snagging.
Source: FAA-H-8083-30B, Chapter 9, Fluid Lines and Fittings; AC 43.13-1B (flexible hose installation practices)
Not the answer
- Provide about 25 percent slack because the hose stretches greatly under pressure
- No slack is needed because flexible hose does not change dimensions
- Install the hose taut with no slack to minimize chafing
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