Afp purge valve

[rvdave]

I'm on the fence about installing the purge valve control although I do have the purge valve which came mounted to the engine. I know that there are methods of starting a hot engine other than the purge valve but wondered if anyone else has been in the same position but installed the control later? Or is the afp system designed around the purge valve? Looking for opinions.

[Carl Froehlich]

I had AFP on my RV-8A and installed the purge valve and single 1/4" return to the left tank (procedure was to have the left tank selected when purging). 800 hours and I think I used the purge valve for a hot start twice - just because I could. I did however use the purge valve on all engine shutdowns to bleed pressure off the spider.

When building the RV-10 I added a 1/4" fitting to the left tank for a purge return. The engine came from Van's so it came with Precision injection instead of AFP. My thought was if I had a issue with hot starts I'd add a AFP purge valve. 350 hours now and no issue with hot starts. The fitting on the left tank has a cap on it.

If however the engine came with AFP injection I would add the purge return to use for engine shutdown.

If I had to do it all over again I'd probably still add the return fitting. It is simple to do when building the tank.

Carl

[gyoung]

Older AFP servos used the purge valve to help kill the engine since idle cutoff didn't completely kill the flow. I don't know if that's changed since I got my circa 2001 servo.

[Don at Airflow]

You probably have an FM-200 if the engine is a 360 or 540. If so it is recommended to use the purge valve for starting and stopping the engine. Since the mixture control in these fuel controls uses a rotary mixture control valve, ICO fuel flow is not zero, therefore there will be leakage of fuel out the nozzles at shut down which causes oil and gook to drain into the air filter box. By using the purge valve the fuel pump pressure is dumped at shut down and there is no leakage of fuel after shut down. The added benefit is that you can circulate fuel in through the fuel system to eliminate hot fuel and vapor from the system before a hot restart and not put any fuel in the engine.

If you do not want this feature, the FM-200 can be converted to the FM-200A fuel control which does not require a purge valve. The cost to convert this unit is around $1500.00 parts and labor.

[n816kc]

AFP system can be set up with or without the purge valve. I am very pleased with the purge valve in my -6 (O-360). Hot starts are a heck of a lot cleaner than with the other fuel injected engines I've flown.

Plumbed the purge line back into the right tank. Push pull cable with a locking button.

[rvdave]

Thanks Don,
That gives me more understanding of the system so I will go ahead and hook up the valve, will have to figure out whether to go directly to a tank or tee into a line. I'm assuming when purging select opposite tank on fuel selector that the valve is teed into?
Is a standard push pull cable normally used? Or locking cable?

[N427EF]

Probably best to install a good quality push pull cable with a lock function.
Mine is from McFarlane and seems to be just right.
It is a .063 wire and push to unlock feature, not the cheapest version and still not overkill for the job.
The termination of an unthreaded cable will be your next challenge and below you'll see how I solved that problem.
A return spring to the open position is optional too.

I've had a purge valve on 2 airplanes and accumulated about 800 hours total
between the two.
Shut down with a purge valve is quick and crisp and helps avoid the "wet dog"
shaking of the engine. Hot starts are essentially cold starts after you purge
your fuel system of heat saturated gas and vapors.

Where you route the purged fuel is really of little concern and best to follow Don's advice.
If you prefer to route it to a tank, you are dealing with much less than a quart of fuel per purge and most of us leave just a little room in the tank to keep fuel from spilling out if you happen to purge it into a "full" tank.

[vic syracuse]

Ernst has a really nice setup here, and while he mentions that the spring is optional, I would recommend that it should always be installed, especially when using the solid wire controls.

Vic

[Carl Froehlich]

Originally Posted by vic syracuse

Ernst has a really nice setup here, and while he mentions that the spring is optional, I would recommend that it should always be installed, especially when using the solid wire controls.

Vic

Did the same thing and also recommend it. The spring was found in the aviation department of Ace Hardware.

Carl

[rvdave]

Ernst, I like the size of that control, do you have a part number I can get from you? Didn't see it at acs.