4mm to 3mm fuel line adaptation, is this Kosher?
 

Okay guys, newbie jet type here with a question on fuel line size adaptation.

I bought this KingCat from a guy last fall, flew it a couple of times before the weather shut us down and now I'm in the process of replacing the Li-Ion batteries, the servo extensions, fuel lines, vent lines, smoke lines, getting rid of the voltage regulators and changing out the rx to a PowerSafe unit.

So I have all this fuel line, vent lines and various Festo fittings and I see this conversion of a 4mm fuel line to a 3mm line where it goes into what I assume was the Propane start port on this JetCat P-160SX which is now a Kero start. The copper colored line going into the engine is actually a flexible line and this connection/adaption to 3mm line size has not shown any kind of leakage or other problems.

Question; is this an acceptable method or should it be converted inside the fuselage with either a brass 4mm to 3mm connector or a Festo 4mm to 3mm connector or can I duplicat this setup? If the latter is okay, what do you recommend for a lubricant to get the 3mm line that far into the 4mm line???

Again, sorry if this is a stupid question but the A&P mechanic in me says this isn't good. The modeler in me says it may be okay and is much cleaner than other possible options. Opinions/thoughts would be appreciated.

Thanks!

Hi Zeeb.

It looks fine (could do with some safety wire) but if it was me I would put a festo reducer further back. Put it far enough back so that the line either side of the reducer is secured to the fuselage side.

Paul.

Not a stupid question at all. I also have a King Cat with a Jet Cat P-160SX engine. You're refering to the "run" side fuel line which connects to the fuel solenoid's 4mm nipple and must be reduced to 3mm to fit the festo connector on the engine. I used a brass reducer, with safety wires, in the fuselage to reduce the 4mm clear fuel line to the 3mm copper/gold colored fuel line. Never had any problem with it in five years.

Jerry

Okay I believe I have some brass 4mm to 3mm reducers (I've bought so much stuff that I cannot remember exactly what I got..lol) and I would think that is the better solution but if the current setup is working and evidently has for some time and it is cleaner, why not duplicate it with new line? I question putting safety wire on the connection though as both lines are flexible? I'm also curious about the "run" side comment. I believe this model was orignally setup with a propane start engine, the gentleman I bought it from was the second owner and he said that he put the P-160SX in the model. It has two fuel solenoids with one labled "P" and the other labled "F". This line that converts to 3mm at the engine comes off the solenoid labeled "P". Also the mechanical JetCat fuel shut off valve is in the line that comes from the "F" labeled solenoid and it's 4mm all the way into the engine. John Redman said I should modify that setup to mechanically shut off both lines while fueling the model.

Another question; I've bought various sizes of the vinyl type lines which are all clear and Tygon for vent stuff, but I've not run across any of the copper colored line as shown in the pic. Is that something special?

The 'copper colored' tubing looks to me like clear tubing that has been discolored by the kero.
Regards,
Gus

Festo or metal, don't rely on two tubes slid into each other… Just because it works, doesn't mean its ideal.

Agreed. Use a connector. Dreamworks sells a 4-3mm barbed Festo that would be ideal.

http://www.dreamworksrc.com/catalog/...-3Mm-Connector

PaulD

OK, may have confused the run & start sides late last night, so here's a copy of the SX diagram from Jet Cat. On mine the "P" solenoid feeds the engine 4mm Festo, and the "F" solenoid feeds the engine 3mm Festo. I believe the "P" & "F" were originally meant to indicate "propane" & "fuel", but they're the same solenoid, so it doesn't really matter other than where you connect them to the ECU. I also have a Festo manual shut off valve in line between the UAT and the fuel pump, which shuts off fuel to everything, which accomplished what John Redman is saying. The copper colored tubing is Festo brand, and I think it originally came with the engine. As far as wire ties go, some do, some don't. Personal preference of added safety. The barbed connector like above is what I used.

Jerry

The only thing holding the telescoped lines together, is a small amount of friction, and hope.
It is a prescription for a fire, if the lines separate while the engine is running.
Get a 3 mm to 4 mm adapter, Festo or barbed to safely connect the lines. There should have been one supplied with the engine.

Thanks guys....

This type of ghettoness is unacceptable. Get a Barbed 4mm to 3mm adapter.