Air flow Performance purge valve???

[pierre smith]

A while back there was a discussion about purge valves and the dangers. What exactly do they do? I looked at an airplane today that has the EM 200 system and suffered an engine failure, blamed on the purge valve.

I need some enlightenment.....Kahuna??

Thanks,
Pierre

[f1rocket]

The purge valve is attached to the distribution block. It essentially allows you to cut all fuel flow to the cylinders instantly. If the purge valve where to open in-flight inadervdantly, the engine would stop.

On the AFP units, the valve has some minor resistance to turning. I have mine spring loaded to remain closed in case the cable were to break.

If I uderstand its use correctly, it is the only way to completed shut off the flow of fuel to the engine. With the throttle completely closed, some fuel still is provided. The other use is to purge the hot fuel in the lines when doing a hot start of the engine. I don't really use it for that since I have the "three fisted start" technique down to an art.

[kentb]

Originally Posted by f1rocket

I don't really use it for that since I have the "three fisted start" technique down to an art.

Randy, could you explain the technique?

Kent

[Kahuna]

The failure mode Im aware of is from the set screws not being safety wired.
Set screw backs out, valve begins to seperate, fuel begins to go into bypass.

Ive been around the block on this one with Don and he was not interested in a design change. The RV-List has a good discussion on this. Several off fields and injuries that Im aware of from this specific issue.

Best

[AlexPeterson]

There was one plane around here that lost an engine right on takeoff because of non-aviation stuff controlling the purge valve. Airplane and pilot undamaged. But, there was a lawnmower cable running the purge valve. I used a nice pushbutton aircraft cable with a rod end on mine. The spring is also a good idea.

[f1rocket]

Originally Posted by kentb

Randy, could you explain the technique?

Kent

This is my description of the standard technique for doing a hot start on a fuel injected engine. Essentially:

1) Throttle wide open, hit the fuel pump for a few seconds
2) Mixture full lean
3) Hit the starter
4) When the engine catches, similtaneously pull throttle and advance mixture

With hands flying around the cockpit, sometimes you need three hands.

[dan]

Originally Posted by Kahuna

The failure mode Im aware of is from the set screws not being safety wired.
Set screw backs out, valve begins to seperate, fuel begins to go into bypass.

This is the biggie. You absolutely gotta check those screws to make sure they're safety wired. The AFP installation manual is very clear about this (big bold note).

The purge valve is your friend but can quickly become your enemy if you or your engine builder overlook an important step during installation.

[Mike S]

Originally Posted by AlexPeterson

There was one plane around here that lost an engine right on takeoff because of non-aviation stuff controlling the purge valve. Airplane and pilot undamaged. But, there was a lawnmower cable running the purge valve. I used a nice pushbutton aircraft cable with a rod end on mine. The spring is also a good idea.

Take a look at this thread, read post 6 from George, looks like exactly what is needed for the purge valve control,--------except the hinge of course.

http://www.vansairforce.com/communit...ad.php?t=17938

Mike

[RV8Squaz]

Originally Posted by f1rocket

This is my description of the standard technique for doing a hot start on a fuel injected engine. Essentially:

1) Throttle wide open, hit the fuel pump for a few seconds
2) Mixture full lean
3) Hit the starter
4) When the engine catches, similtaneously pull throttle and advance mixture

With hands flying around the cockpit, sometimes you need three hands.

For hot starts on my IO-360A1A I've been doing it this way with a lot of success:

1) Mixture - full rich
2) Throttle - cracked 1/4"
3) Fuel pump - on for a split second, then off
4) Mixture - full lean
5) When the engine catches, advance mixture

The advantage of doing it this way is I only have to move one lever. It works, because I operate the the pump only long enough to get fuel back in the injector lines so therefore the engine doesn't receive enough fuel to get flooded. I'm not saying this is the right way or the method above is the wrong way. It's just what happens to work for me and I like it. In addition I have my starter button on my Infinity stick grip so there are less hands flying around. I too don't have three hands.

Jerry

[Kahuna]

Originally Posted by pierre smith

A I looked at an airplane today that has the EM 200 system and suffered an engine failure, blamed on the purge valve.

I need some enlightenment.....Kahuna??

Thanks,
Pierre

Pierre what was the purge valve failure mode in this case?
Was anyone hurt?