AFP Purge Valve Operation

ExtraKatana · #1 03-02-2011, 05:26 PM

Bought a 6 with the AFP FI system and purge valve.
Engine is an IO-360 9:1
Can someone walk me through the prescribed method for shutdown and Hot Starts? The specific reason for the valve? (I have heard that with this system full lean does not provide enough fuel starvation to kill the engine) I believe there is a purpose for this.....other use for the valve? The vent is to the starboard tank.
Thanks for your help!

Mike S · #2 03-02-2011, 05:30 PM

I am still learning the entire fuel injection thing, but here is what I have learned in 30 hours.

Shut down the engine with the cutoff valve. Leave it in the cutoff position till you are ready to start the engine again, be it in 10 minutes, or ten days.

For hot start, I just close the bypass valve, and twist the key.

No boost pump, mixture full rich, throttle cracked a bit.

Good luck, hopefully Don will jump in here and give a better lesson than I can. If you havent yet figured it out, Don is a regular here, and is extremely helpful.

Geico266 · #3 03-02-2011, 05:34 PM

The valve can be used for several things.

1. Killing the engine, like Mike said. Just open the value and fuel is stopped from feeding the engine.

2. Purging the hot fuel from the system for a hot start. Place the fuel selector on left, open the throttle and mixture to full rich, purge valve open. Run for 30 - 40 seconds. This should push the hot fuel into the right tank, but you will need to check the plumbing on your plane.

3. Hot Start (For my -10, I0-540) (If you have a problem starting hot then this may help). After purging the hot fuel out of the system (#2) close the purge value, set the throttle 1/2 way open, mixture full lean. No prime. Crank the engine until it fires and instantly move the mixture to near full rich while at the same time moving the throttle to idle. This takes a little practice and make sure you are ready for the engine to run at 1/2 speed.

Your milage may very because it is an I0-360. Maybe the old owner could give you some tips.

Good luck and let us know how it goes.

Captain_John · #4 03-02-2011, 06:05 PM

This is an interesting thread to me because I am really considering Don's system.

I know the purge valve. It is adjacent to the spider, right?

But what/where is the cutoff valve? I am pretty sure it must cut off flow somewhere in the fuel line(s) but where? Where do people usually put it?

Also, are these operated by push pull cables or solenoids?

Don, when you chime in could you provide us with an overview of the components from a newbie's perspective?

I have hundreds of hours operating the Bendix system but am totally green to the Airflow system.

CJ

Mike S · #5 03-02-2011, 06:18 PM

Purge valve, cutoff valve,----->same thing.

Yes, mine is mounted to the spider.

ExtraKatana · #6 03-02-2011, 06:31 PM

I currently let idle at 1k RPM and "gingerly" pull back the cutoff cable. The engine stops flawlessly. I just want to make sure the settings (1k/full rich) are correct......the "AFP manual" method.

Fuel tank selector on "left"makes sense and hadn't thought of that while purging B4 hot start. I guess you could be sending bubbles to the clunk or more hot fuel if still on the right tank.

Thanks!

hydroguy2 · #7 03-02-2011, 06:34 PM

CJ, go for the gold. ...well at least my AFP spider and purge valve are gold anodized. You won't regret it.

I only have 19hrs on mine, but have not had 1 single time I wish it were something else. Works PERFECT every time. I operate mine just like Mike. If you shutdown with the purge valve(cutoff) the engine stops instantly. and no chance for fuel to leak down fouling your intake plenum. I don't have a sniffle valve, but not really need if you never have fuel leaking.

Cold starts...easy as pie
Hot starts...easy as hot apple pie.

N427EF · #8 03-02-2011, 09:42 PM

I had an AFP on my 8 for 450 hrs and I am installing one on my 10 at this time.
The purge valve is a brilliant solution to an old problem in fuel injected engines where hot starts can be a problem at times.
As all the other posters mentioned it serves as a positive shut off up near the spider where most are installed.
For shut downs it's a no brainer just pull the valve and the engine quits.
For starts, there are several ways to make use of it and all are described in the manual that you should have received when you bought your 6.
Rather than give you a specific way to get the engine started it may be more helpful to you to simply describe what you can do with it.
Opening the purge valve with the mixture set rich allows you to circulate fresh fuel into the system and purge hot fuel and vapour from the entire fuel system.
You won't be guessing anymore if maybe you primed enough or not or flooded the engine and you are set up for a quick start.
The return line can be plumbed in many different ways as described in AFP's
fuel diagrams. Yours seem to go back to the left tank.
It took me quite a few hours to acquire the finesse to get a hot engine started on a blade or two but once you develop a sense for what your engine wants on hot starts, it will impress you every time.

ronschreck · #9 03-03-2011, 03:55 AM

Quote:

Originally Posted by Mike S

I am still learning the entire fuel injection thing, but here is what I have learned in 30 hours.

Shut down the engine with the cutoff valve. Leave it in the cutoff position till you are ready to start the engine again, be it in 10 minutes, or ten days.

For hot start, I just close the bypass valve, and twist the key.

No boost pump, mixture full rich, throttle cracked a bit.

Good luck, hopefully Don will jump in here and give a better lesson than I can. If you havent yet figured it out, Don is a regular here, and is extremely helpful.

Plenty of posts here describe how to use the purge valve. Mike, since you recommend leaving the valve closed after engine shutdown it is implied that there you have no spring on the valve actuator arm to hold it open. This is a safety issue since failure of the cable attachment to the purge valve could allow the valve to close in flight resulting in fuel starvation to the engine. A return spring should always be attached to the purge valve actuating arm to hold it open.

Don at Airflow · #10 03-03-2011, 07:05 AM

The purge valve is a cable operated valve. There is no other ?shut off valve? in the system.

Here are the instructions from the manual

OPERATING INSTRUCTIONS FOR USING THE PURGE VALVE

5-5. The following instructions are recommended procedures for operating engines with engine driven fuel pumps.

COLD STARTS
* Purge valve off (?ICO? position).
* Mixture control "FULL RICH".
* Throttle open ? or more.
* Turn on boost pump. Run for 30-45 seconds
* Put purge valve to run (?R? position), count to five then return purge valve to off position. Actual prime time may be different from installation to installation. If the engine tends to flood, reduce the throttle to off idle then prime the engine.
* Reduce throttle to 1/8 or off idle.
* Leave the Mixture control in the full rich position.
* With mags "HOT?, crank engine, when engine fires, put the purge valve in the run position and the throttle to idle. After the engine stablizes idle, the boost pump can be shut off.

ENGINE SHUT DOWN
* Bring engine to idle speed.
* Leave mixture control "FULL RICH".
* Turn boost pump off.
* Put purge valve control to "OFF" position.
* Turn off the ignition.

HOT STARTS
* Mixture control "FULL RICH".
* Throttle ? to wide open.
* Purge valve "OFF" position.
* Turn on boost pump and let run 30 to 45 seconds. This will purge the hot fuel and vapor from the system, and will cool and fill the fuel system components with cool fuel.
* Leave the boost pump on.
* Set Throttle to 1/8 open.
* Give engine a short prime by putting the purge valve to ?run? then back to ?off?. The amount of prime required my vary from installation to installation.
* Leave Mixture control "Full Rich?.
* With mags "HOT?, crank engine, when engine fires, return throttle to idle and purge valve to ?Run".
* Leave the boost pump on during hot, low power, operation.

Another method for starting the engine when hot is to leave the mixture ?rich? after purging the system. With the purge valve in the ICO position and the throttle at idle, crank the engine while slowly moving the purge valve to the Rich position. The engine will start during this movement to the Rich position.

As far as the installation goes, depending on the type of control cable used to control the purge valve, a return spring may not be required. If you have a carb heat type cable (wire with a drilled bolt attachment) then a return spring that will pull the purge valve to the rich position is recommended. The analogy is ?do you have a return spring on the mixture control, throttle control?? If using good quality cables with solid threaded ends and spherical rod end bearings on the cable, return springs are not necessary.

ExtraKatana you should have a 180 + page manual on the operation and service of the fuel injection system. If you do not have this document and or have not registered the fuel control system with us, it would be best to give us a call and we can get the information to you need.

Don