Due to the cost, weight and reliability of flexible hoses, they should only be used where needed. By "needed" I mean where a fluid connection between two components that move relative to one another.

I was able to eliminate the fuel hoses in the wing root area by incorporating a pressure bulkhead at the aft spar penetration (see picture). This allowed the fuel lines to be connected after the wing was mated.

If you are building with synthetic rubber hose in the fuel system, be sure to do a flow test prior to first flight

Regards
Brent Regan

From Feb 2006

Fluid lines, like everything else on your airplane, deserve careful consideration before application. There are several technologies available and each has its advantages and disadvantages. There is no single solution that works best in all situations.

Aluminum hard line is the lightest and cheapest. It is easy to fabricate and, with careful installation and chafe protection, will last the life of the airframe. Aluminum hard line is suitable for hydraulic, brake, fuel and vent lines aft of the firewall where both ends are stationary.

Stainless steel hard line is three times heavier than aluminum but still lighter and cheaper than hose.  It is well suited for high vibration and higher temperature  applications where  where both ends are stationary or nearly stationary.  I used stainless hard line between the gear legs and brake calipers  by bending the tube into a 540 degree loop so it would act as a spring. I also used it firewall forward for the on firewall plumbing and the on engine plumbing. I used -4 fire sleeve to insulate fuel supply and distribution lines to reduce hot soak fuel vaporization.

Teflon/ stainless braid/ silicone hose (Stratoflex 124J) is the best solution for firewall to engine and nose gear actuation cylinder connections. It has an infinite service life and should be replaced on condition. Sacramento Sky Ranch has an excellent policy where they will fabricate, clean  and pressure test a hose assembly and send it to you with an unconditional satisfaction guarantee. They will replace it if it is the wrong length even if you told them to make it the wrong length. Weight is 6 to 10 times that of aluminum but less than rubber hose. Over the service life of the aircraft, these are the most economical hoses.

DH Instruments test hose is the best solution for the flexible portions of the brake lines (gear leg and petal cylinders). They have been exhaustively covered in previous threads.

Aeroquip 6xx series (synthetic rubber / stainless over braid) with field terminable ends is an aesthetically attractive hose that is well suited for hot rod show cars but has limited application in aircraft, particularly composite aircraft. The only apparent advantage of this hose is that the components (hose, fittings, fire sleeve and clamps) can be purchased for ~60% the cost of a similar assembled, cleaned and tested 124 assembly.  Disadvantages include; stray over braid wires (AKA "Meat Hooks"),  ID Bore contamination from manufacturing, finite service life, abrasive outer braid, tendency for the fitting to skive a flap out of the hose ID during assembly, poor termination consistency due to inexperienced assembler and a tendency to kink. You are giving up a lot to save 40% on a dozen hose assemblies. Assembly labor time is comparable to the aluminum hard line fabrication time. These hoses are the supermodels of the hose world, pretty to look at but expensive to maintain, a bitch to live with and no ability to age gracefully. That shiny over braid will grind through any painted, composite or aluminum surface it touches. Did I mention it is conductive? Great fun near anything with electricity flowing.

Nylaflow and Poly-flow non-reinforced tubing is suitable for pitot static system, door seal pressure system, pilot relief and low pressure 02 (not to be confused) plumbing. Non-reinforced aquarium tubing should NOT be used  in the brake system. It WILL fail.

One additional tip that expands on the hose pressure test, during building it is handy to be able to test the various valves and actuators. This can be done by connecting the pressure supply line to compressed (shop) air. This lets you check gear and flaps range of motion and geometry safely  without flooding the shop with red oil (5606). A secondary advantage is that you can bubble leak check all the fittings before putting oil in the system. Be sure your shop air is dry and adding a few drops of air tool oil will keep the valves and actuators lubed.

Regards
Brent  Regan