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Purge Valve Question

D

DBone

Well Known Member
I'm totally new to FI, so I'm trying to get my hands around what I need and don't need.

I had a deposit in at Superior for an IO-360 with the Precision Silverhawk FI. From what I remember figuring out at the time (a while ago), was that I didn't need any special plumbing and definitely nothing back to the tanks. I talked to Andy at Andair, and he knew exactly which fuel selector valve I needed to make the whole system work.

Fast forward to today, and I am most likely going with a Lycoming IO-360 with an Air Flow Performance system, and I am reading about the purge valve setup. I left a vm for the folks at AFP, but I thought I'd ask hear as well.

Will I need to buy any additional components to make the AFP system (with the purge valve) work, will I have additional components that I need to get rid of, or will what I have handle the new setup?

Thanks for helping a newbie out!
 
You should be fine with what you have, you will need to add a return line, this usually goes back to one of the tanks.

The return line is not usually valved, as it is not a continuous flow----just when in the purge position.

You could just plumb it back into one of the feed lines, but that will defeat the idea of running cool tank fuel through the heat soaked system on a hot start.

Give Don a call at AFP, good guy and very helpfull.

Good luck
 
You wont need Vans control bracket (VA-182?), as this is supplied by AFP. Others (me, other Checkoway followers), have plumbed the purge line back into one of the supply lines instead of back to a tank. If you purge to the supply line from the right tank (for example), and set the fuel selector to the left tank, you wont be recirculating hot fuel.

erich
 
The purge valve is only used in certain circumstances anyway and you will probably not be running it enough to recirculate hot fuel. As for the mixture bracket thing, I found that it was difficult to route on my -6A and it looks like you will have similar fun with the -7. I'm assuming vertical induction? Anyway, here's my approach, complete with pictures.
 
N184JG said:
I use the purge valve for every start and every shut down per AFP.
Click to expand...

Shutdown, I can see. Every start just doesn't make sense - you only need it for hot starts or any other situation where the fuel on top of the engine in the divider and injector lines has been heated.
 
Greg

With wingrrot fuel pumps you can simply turn off the pumps until the engine quits..I agree, purge for hot starts only

Frank
 
I use my purge valve for every shutdown, it works much better than the mixture control, the engine just stops right now.
As far as hot starts, it depends on the hot start...if you are starting right up like say after a quick fuel stop, I just start cranking as I push in the purge cable...usually the engine is running right as its completely closed (allowing fuel to flow to the divider).
If I've been sitting awhile and its a hot day, I'll go through the purge routine.
My 1/4" return line is tee'd into the left tank line ala Checkoway, so I always use the right tank for purge valve hot starts...works great.
 
Last edited:
airguy said:
Shutdown, I can see. Every start just doesn't make sense - you only need it for hot starts or any other situation where the fuel on top of the engine in the divider and injector lines has been heated.
Click to expand...

You don't understand the purge valve at all . Its not used just for hot starts it works much better then the mixture for starting a cold engine. With the fuel pump on close the purge valve to prime the engine then open crank engine as soon as engine starts close purge valve mixture is full rich all the time. This is per AFP.
 
N184JG said:
You don't understand the purge valve at all . Its not used just for hot starts it works much better then the mixture for starting a cold engine. With the fuel pump on close the purge valve to prime the engine then open crank engine as soon as engine starts close purge valve mixture is full rich all the time. This is per AFP.
Click to expand...

I beg to differ. I do understand the purge valve, both it's function and it's operational purpose. My point is that it's not needed for a cold start. Using it is no detriment, but neither it is a great advantage, and it's certainly not required. The purge valves specific purpose is to recirculate fuel from the flow divider back to the fuel supply, (hence the name PURGE valve) which has the side effect of dumping all the pressure on the injector lines which allows it to be used as an excellent idle cutoff tool. The whole operational point for the existence of the purge valve is to solve hot start problems by removing heated fuel from the FWF area.
 
airguy said:
I beg to differ. I do understand the purge valve, both it's function and it's operational purpose. My point is that it's not needed for a cold start. Using it is no detriment, but neither it is a great advantage, and it's certainly not required. The purge valves specific purpose is to recirculate fuel from the flow divider back to the fuel supply, (hence the name PURGE valve) which has the side effect of dumping all the pressure on the injector lines which allows it to be used as an excellent idle cutoff tool. The whole operational point for the existence of the purge valve is to solve hot start problems by removing heated fuel from the FWF area.
Click to expand...

But it is convenient.

I am still on a learning curve with it but I am having success using it as a primer valve on a cold start , about 5 seconds on, then off, hit the starter and when the engine fires back to on. If one did not use that procedure, you'd have to do the same thing with the manual mixture lever or the engine would be flooded or you'd have to turn the pump on and off.

I was messing with the idle mixture setting yesterday, it is very sensitive. A one flat adjustment is noticeable. I will not crawl down to make that adjustment while the engine is running as it is about 10" from the prop but it can be accomplished starting the stopping the engine. Don says go fly and then fine tune it after the break in...so that's the plan as soon as I get the oil temp gauge to work which should be as soon as a package arrives from GRT.
 
Silverhawk with no purge

Guys, I have the silver hawk fuel injector. So I don't have a purge valve. Is this a big mistake? I bought my IO360 M1B factory direct from Lycoming through vans. Is there a way for me to install one? The distribution hub on the top of the engine has a AN4 NPT-to-flare fitting on it that is supposed to hooked up to something. Is this where I hook one up? or is that where I get my fuel pressure sensor to connect to? Thanks for the advice. -Brad
 
Search the threads for Hot Start info...

flyingbeaver26 said:
Guys, I have the silver hawk fuel injector. So I don't have a purge valve. Is this a big mistake? I bought my IO360 M1B factory direct from Lycoming through vans. Is there a way for me to install one? The distribution hub on the top of the engine has a AN4 NPT-to-flare fitting on it that is supposed to hooked up to something. Is this where I hook one up? or is that where I get my fuel pressure sensor to connect to? Thanks for the advice. -Brad
Click to expand...

I do not have a purge valve. It took a bit of experimenting but I found a Hot Start procedure that works well for my set up. They are all different. I usually start on a Hot Start within 6 blades if not sooner. Once in a while, I need to re-engage, but rarely.
The biggest challenge is to know, when is it a Hot Start? You learn this too so after you have been sitting on a hot ramp for a few hours, do your Hot Start procedure, it does not catch, well, do a normal cold start and off you go. You will learn all of this. I learned it and never drained a battery or got stuck somewhere.
I suspect a purge valve makes procedures a little more consistent and less thought in regard to if it is a Hot Start condition or not.
Consider these things before going through the expense and work to install. However it is not that difficult to do and can be added in.
 
flyingbeaver26 said:
Guys, I have the silver hawk fuel injector. So I don't have a purge valve. Is this a big mistake? I bought my IO360 M1B factory direct from Lycoming through vans. Is there a way for me to install one? The distribution hub on the top of the engine has a AN4 NPT-to-flare fitting on it that is supposed to hooked up to something. Is this where I hook one up? or is that where I get my fuel pressure sensor to connect to? Thanks for the advice. -Brad
Click to expand...

Check with Don at AFP. He knows more about all these systems than anyone here.
 
flyingbeaver26 said:
Guys, I have the silver hawk fuel injector. So I don't have a purge valve. Is this a big mistake? I bought my IO360 M1B factory direct from Lycoming through vans. Is there a way for me to install one? The distribution hub on the top of the engine has a AN4 NPT-to-flare fitting on it that is supposed to hooked up to something. Is this where I hook one up? or is that where I get my fuel pressure sensor to connect to? Thanks for the advice. -Brad
Click to expand...
NO. Hot starts are not a problem with the Bendix (Silver Hawk) type injection system. As noted above, this is much ado about nothing with the easily acquired technique.
 
flyingbeaver26 said:
Guys, I have the silver hawk fuel injector. So I don't have a purge valve. Is this a big mistake? I bought my IO360 M1B factory direct from Lycoming through vans. Is there a way for me to install one? The distribution hub on the top of the engine has a AN4 NPT-to-flare fitting on it that is supposed to hooked up to something. Is this where I hook one up? or is that where I get my fuel pressure sensor to connect to? Thanks for the advice. -Brad
Click to expand...

I have the Silverhawk on a TMX-IO360 M1B with no purge valve. Hot starts are as simple as:

Try a normal start. If that doesn't work, pull the mixture to idle cut-off and crank till she starts, then slowly feed the mixture control in.

No other steps necessary. No fiddling with the throttle or other stuff, period. I do have an LSI Plasma II and one mag with impulse coupling. I have both switches on to start. Maybe, thats why mine starts so easily?
 
I was discussing this subject of a purge valve with the current owner of the Cozy MKIV we built. It is powered by a Superior XP IO-360 and after a short period of trail and error during taxi testing, hot starts have never been a problem without a purge valve. I don't plan on installing one in my RV-10. It adds time, costs, and complexity for a problem that does not exist provided proper starting proceedures are followed. I don't see how an IO-540 would be any different from an IO-360. I may be proven wrong later, but if thats the case I will install one then.
 
Silverhawk question

My silverhawk distribution manifold has a NPT-flare port on it. Its the fitting with the red cap on it in the picture below. Since the silverhawk has no purge valve, what does this fitting do? Is it used to sense fuel pressure? My factory direct Lycoming engine came with this FI system but they do not include any instructions for it.

IMG_0348.JPG





2nd question, a little off topic. The throttle body has four 5/16th nuts that secure it to the sump. Do these nuts require the star-type lock washer to be used on them? Torque should be 110 - 150 "/#'s? I have no instructions on this so your advise is very helpfull.



IMG_0351.JPG


Thanks,
Brad Vier
RV-8 FWF
 
Picture 1, red cap is at head pressure for the spider. Fuel Pressure could be had from here. Its not for the purge valve. If not used, remove that fitting and put in a plug.

Picture 2, yes a lock washer, star or split, should be used there.
 
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