Skyfox/Gazelle Fuel Line Non Return Valves

[Neil Denmark]

Has any owner of a Skyfox or Gazelle got experience with changing out the fuel non return valves located between the wing tanks and collector tank behind the seat? The rubber inside the brass fittings of non return valves are known to deteriorate with age but I can't find any info on where to source replacement parts. Is there a more modern non return valve I can use?

Thanks

[skippydiesel]

You can get  fuel non return valves from automotive or aircraft suppliers. The aircraft suppliers will almost always be more expensive.

 

The type of fitting will depend on if you are using a press fit into a "rubber" tube or attaching to a metal (hard) line. Non returns valves are also known as check valves.

 

 This is an automotive valve for press fit, with the type of bayonet /spigot fitting I proffer. The alternative is the serrated type press fit.

Automotive AN style for hard line. Come in a wide range of end sizes  & types.

Aircraft non return AN fittings both ends. Thes can be turned into press fits by purchasing screw on "tails"

 

 

Some websites you may care to brows:

https://www.aircraftspruce.com/catalog/appages/acscheckvalve.php

https://aeroflowperformance.com/

https://www.aaestore.com.au/

https://www.asapspares.com.au/

 

[Neil Denmark]

Thanks for your help SkippyDiesel! I have bought a couple of non return valves from an auto shop which gives me the confidence to go ahead and  remove my original ones from the A/C and inspect the internals without the hazard of being grounded for weeks while I try and find replacements!

[skippydiesel]

Hi Neil,

 

Some non returns/check valves have a relativly high opening pressure - if specifications for the ones you purchased are available be sure to check.

 

I assume you are running a Rotax 9 series engine - the various pumps usually operate at quite low pressures (Max 7 psi?). The Gazelle being a high wing (fuel in wing?) may mitigate this to some degree.

[Thruster88]

Good point Skippy, from the description of the fuel system the pump(s) will be after the collector tank so they will be sucking thru the non return valves. To much resistance could lead to vapour lock/ fuel starvation. 

 

Is the collector tank vented? In which case only the gravity head pressure is available to overcome the non return valve. Fuel systems are not always as simple as they seem. 

Edited August 2 by Thruster88

[skippydiesel]

Out of idle curiosity - why do you have non return valves? ie what is their function in your aircraft system?

[facthunter]

To prevent unwanted transfer of fuel or air entering the system.  Nev

[Neil Denmark]

Hi Guys and thanks for all your great input into what might seem like a simple topic - but is not!

I have asked myself 'what is the purpose of the non - return fuel valves'.  All I can come up with is that the two main (high wing) fuel tanks are "self leveling" i.e. there is no valve to select right/left tanks which is great! If you were to fly/park at a weird attitude the NRV's would stop fuel from flowing back to the lower tank (and possibly overflowing if full)?

The Gazelle Maintenance Manual specifies a minimum fuel flow to the carbs of 500 ml/minute (combined total) which I will test once the new NRV's are installed.

The fuel pump is located after the collector tank and provides only about 4PSI. I'll let you know how the flow test goes!

These are the non return valves I was able to buy online:

[skippydiesel]

Neil -

 

I don't much like the serrated push fit connectors - check out the one that I illustrated.  This sort of connecter is almost bound to leak over time. 

 

When you match the hose ID, with the fitting OD, the clamp is just there for security (not leak prevention). The best fittings, have one raised ring, slightly larger than the ID of the pipe and a plain shaft the same OD as the ID as the hose. the clamp should be fitted close to the raised ring to prevent slippage.

 

The aviation non return valve has a very low opening pressure -what do your new units open at?  Test your new units at almost empty tank - remember the pressure will drop as the tank level gets lower.

[Neil Denmark]

Thanks Skippydiesel. I am still hoping to be able to reuse the ones that are in the A/C but seeping... I will have a go at these tomorrow. I have no idea what the opening pressure is for these auto valves - there are very little specs available. Yes tanks will be low level for test.