fuel line orifice

DaveJaksha

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Joined
Feb 14, 2016
Messages
186
Location
Tucson
Aircraft
Sportcopter Vortex
Total Flight Time
100
[FONT=arial, helvetica, sans-serif]Ok, time to ask the big brain....I am installing the fuel lines for my FI engine. I need to install a small orifice ( 0.015") between the fuel pump outlet and the return line from the pressure regulator. This is to allow any air that gets into the system to return to the tank and bypass going to the injectors. The orifice also will allow the pressure in the lines to drop after shutting down the engine. Anyway, I am using AN fittings. Anyone got a clever way to fabricate this? I was thinking of maybe using a double ended male fitting and plugging it up and then drilling the orifice? [/FONT]

Cheers,

Dave
 
My pressure after shutting down will drop from 30 lbs to zero in about an hour,if you are

worried about it just crank the engine with the fuel pumps shut off the pressure will zero out.

Also if you are getting any air into the fuel system that's the problem that needs fixing.
.
 
Hi, Eddie. Yes, I agree, any air leak should be fixed. But, for some unseen reason air or fuel vapor should get into the pump, it takes a fair amount of time to clear through the injectors. The orifice will allow the air/vapor to escape before trying to pump it through the injectors. The fuel pumps typically pump air/vapor at a low pressure until the pump prime again. Maybe never needed, but, I feel a good precaution.

Dave
 
Dave,
You can get an AN coupling blank (for an example; -6 male x -6 male coupling) the fitting has male AN by male AN with a non-drilled center section, this allows you to drill your own orifice.
Allen Aircraft is a good source. What size AN fitting? I may have an assortment, I could drill one for you and send it for the cost of shipping.
 
GMAN, thanks for that info. I didn't know that you could get male-male coupling that was blank. I am looking for a AN6. Thanks for your
offer! Let me know if you have one. Otherwise I will order one Allen.

Dave
 
I have a -6, screwed in center blank. What size orifice do you want? I'll need a ship-to address.
 
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Done! Here are a couple pics.
 

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Two big thrums up to you Gman! I'll pay it forward for someone else.

Dave
 
I have worked in Auto Mechanic's almost 30 years and I tell you if your fuel pump is taking in air you have a problem somewhere in your delivery line.
before trying and putting a patch on it with your return line orifice I would try to find why it's taking in air.

can be many things.

Bad Pump
pin hole in hose or line
bad connection
and the list goes on.

if this was a road going car it would be ok you can always pull to the side of the road. but in a plane it's a different story.
So please fix your real problem and don't just patch it.
 
Hi, Franks. Thanks for your comments and advice. Please understand the introduction of a bypass orifice is not intended as a patch for a normally operating fuel injection system. It is, in my opinion, a safety device for a maIfunctioning fuel system. It is placed between the high pressure side of the fuel pump and the final 10 micron filter that supplies the fuel rail. If for some reason air, or more likely vaporized fuel were to exit the fuel pump, the orifice allows it to pass to the low pressure fuel regulator return line and then the fuel tank. Of course, in normal operation, some fuel will pass through this orifice also, but the small size insures the amount is negligible. As Eddie mentioned in post #2 the high pressure side of the fuel system can maintain pressure for quite some time after the engine is shut down. I have worked on some systems that still hold pressure hours after shutdown. The bypass allows the pressure to leak down pretty quickly after shut down so if you need to open the fuel system for some reason you won't be surprised by a spray of fuel from residual pressure It also reduces the strain on the hoses and injectors.

So I think it is a simple addition, that really doesn't have any downside, and may keep the engine running long enough to allow you to make a safe landing.

Cheers,

Dave
 
Interesting, this showed up in my email today from [email protected].......

“As per the ROTAX 912 Series installation manual, a Mandatory “restricted” fuel return line is required to be incorporated within the aircraft’s fuel system. The purpose of the fuel return line is to bleed off any vapors that may form within the fuel system that could cause vapor lock, resulting in a possible loss of engine power.”

Dave
 
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