How does a fuel spider work?

Just curious how the spider actually works on say an IO-360. I know the servo controls the amount of fuel to the spider but does it just split the fuel and that's it? Is there always pressure at the cylinder and it just takes what it needs?

I'm just thinking of cars that are told when to put fuel in the cylinder electronically or with a fuel distrubuter.

Yes, Mainly..

...but on some systems, the spider has a spring-loaded diaphragm that takes a preset psi to open. When you pull the mixture and the flow stops, the diaphragm closes, so the fuel is positively cut off and you don't get intermittent run-on.

Best,

boom3 said:

Just curious how the spider actually works on say an IO-360. I know the servo controls the amount of fuel to the spider but does it just split the fuel and that's it? Is there always pressure at the cylinder and it just takes what it needs?

I'm just thinking of cars that are told when to put fuel in the cylinder electronically or with a fuel distrubuter.

Click to expand...

The workings of the flow divider are a bit more complex than the auto electric injector. Don Rivera does an excellent presentation on this subject at his Fuel Injection 101 course, I wish I had kept notes. I do recall that each injector is vented to atmospheric pressure and it is that pressure difference between it and the intake area that pulls fuel into the chamber, and further upstream in the divider there is a diaphragm that controls fuel through it at a pressure of 1-3 psi. The inner workings of the fuel controller are also very interesting. It is amazing how well this totally mechanical system works.

The course is so good, I am thinking of doing it again.

Flow Divider Operation

Here is what a Flow Divider (spider) is actually for and how it works.

First you have to understand a little about the fuel injection system. The Injector nozzles on these systems (Airflow Performance and Bendix/Precision) use what?s called an air bled injector nozzle. The nozzle has a fixed orifice size that?s sized according to the fuel pressure available to the fuel injection system and the maximum fuel flow through the injector nozzle. Therefore, with the limited fuel pressure available (usually around 20 ?30 PSI) the nozzle orifice is fairly large (usually .028? diameter on 360 and 540 engines). At idle the pressure drop across the injector nozzle is less than 0.02 PSI, so if the nozzles are not level (tail dragger) or the flow divider is above the nozzles the fuel distribution to each nozzle will be poor, and the engine will not idle. Further more at shut down the valve in the flow divider will shut off each nozzle port tending to keep the nozzle lines from draining out, promoting a cleaner shut down.

The flow divider has a precise metering slot at each port. The valve in the flow divider opens and closes this port based on the total fuel being delivered to the flow divider. The valve, which is connected to a diaphragm, has a spring that sets a 1.5 to 2.5 PSI pressure differential across each metering slot. If you look at the division at 2 PSI, which is equivalent to approximately 70 inches of fuel head, the fuel in each nozzle would be divided equally to each nozzle even if the nozzles had a difference in height of 50 inches. As the total flow increases the valve in the flow divider continues to open as nozzle pack pressure increases. At the higher fuel flows the flow divider valve is open so that the area of the flow divider port is somewhat larger (10X in the Airflow flow divider) so that the injector nozzles then divider the fuel to each cylinder.

This is a simple concept but a very demanding component to manufacture. So basically if you didn?t need to idle the engine you could do away with a $500.00 part.

Hope that helps with the understanding. If not we have a FI 101 class on the first week end in November 2010. Still seats available.

Don

Don, easy for you to say, but...

Not so easy for me to understand. I think that I need to take your class, but November is out for me. What is the schedule for next year and where are the classes held?

Is there routine maintenance that is needed for the spider?

Kent

Flow Dividers and FI 101 classes

I tried to explain it as simply as possible, but some times having you hand on the parts and seeing it work help too.

The 2011 class will be the first weekend in March. You can email Colleen if you want class info at [email protected].

Don

FI-101 is a _Great_ class

I have to chime in here and say that Don's FI-101 class is fantastic. I went down with _zero_ knowledge about fuel injection systems, and came away with a good working understanding of mechanical fuel injection. Don takes the "freaking magic" out of it all. He isn't kidding when he says that having your hands on the parts makes a difference. Don explains things in a way that had lightbulbs coming on for me the first day.

Not only is the class itself great, but Don fires up the grill (at least, he did during the class I was there ... hopefully he still does) and everyone sits around and eats dinner and talks airplanes for hours after the class itself is over. A great class, and great hospitality. Can't beat it.

So if you are _at_ _all_ tempted, make the trek to Spartanburg, SC and take the class. I am not affiliated with Airflow Performance in any way, but am simply a very happy customer.

Gee Dwight, you make it enticing

It would be worthless to me in my little O-360-A1A powered racer but I feel any more gains in speed are going to require changes in the propulsion system. The education couldn't hurt although another thread made it clear that carburetors allow identical engines to produce more power in my race regime.

Bob Axsom

Thanks Don, great explanation. I don't have my head quite all the way around it, but definately get the idea.

Fuel spider divider

Is it possible for there to be a glog in the fuel divider or spider in the IO360 such that one cylinder isn't getting enough fuel under climb demand?

I'm asking because I'm chasing a high egt. Brand new YIO360-M1B with 5 hours. It runs normal at idle but then at take off climb out it jumps up to 1500. It is not the plugs. Not the probes. I'm cleaning the nozzle now, and test it tomorrow. But if its not the nozzles then what?

So I'm wondering if there could be a restriction in fuel flow inside the spider. If so can I just take it apart and clean it?

thanks

sglynn said:

Is it possible for there to be a glog in the fuel divider or spider in the IO360 such that one cylinder isn't getting enough fuel under climb demand?

I'm asking because I'm chasing a high egt. Brand new YIO360-M1B with 5 hours. It runs normal at idle but then at take off climb out it jumps up to 1500. It is not the plugs. Not the probes. I'm cleaning the nozzle now, and test it tomorrow. But if its not the nozzles then what?

So I'm wondering if there could be a restriction in fuel flow inside the spider. If so can I just take it apart and clean it?

thanks

Click to expand...

Yes, but less likely. Your problem is a partial restriction. Partials are much more likely at the injector, but possible at the spider. Full blockage is more or less equally likely at both. If you look at the injector before you clean it, you should be able to see the blockage by holding it up to a light or the sun.

If cleaning the injector doesn't work, next step is to clean the spider. It is relatively easy to disassemble and check/clean.

Larry

Just experienced a sudden injector failure in my buddies Cozy MKIV a couple weeks ago down in Florida while he was practicing instrument approaches at Punta Gorda and I was safety pilot. The shaking from the miss firing cylinder made us think we lost a prop blade or part of one. The #4 cylinder went dead by the time we got the plane back down. The first thing we checked was the plugs. #1,2 & 3 were covered with soot and #4 was clean and mostly dry. Ten years on the plane since new and over 700 hours and the injectors were never serviced. I pulled the injector assemblies and found #4 had an obstruction near the tip of the sleeve. Put them in some marked plastic cups to not mix them up and gave them a 24 hour soak in Hoppes #9. A soft brass bristle brush finished the cleaning but the obstruction remained in #4. I didn't want to risk damaging the injector sleeve by digging or poking it out so the rubber tipped air nozzle blew it out in reverse. Could not locate the piece afterwards to try and identify it. Cleaned the fuel filter and the servo filter, flushed the fuel lines with fresh fuel and it runs fine again.

Hoppes #9

Lycoming service bulletin says 20 minutes in Hoppes #9. Maybe the are overly cautious but that's what I follow.

Gary

Just had a partial blockage and could see the debris. While hopps can work, I just used laquer thinner and a toothpick to clean the orifice, followed with an air blower. The soft wood can't hurt the brass restrictor. Worked fine.

Larry

Dan...Great article

Thanks