Airflow performance purge valve

[togaflyer]

Thinking on adding the AFP purge valve. Lots of summertime flying in Florida and Georgia and I would like to finally end the hot start lotto. I use Dan’s method along with the old flood it and burn it, and have never been left stranded. But I’m thinking the purge valve would insure a simple, non dramatic start every time. Is it worth installing and does it really deliver a normal start when everything is vapored. Currently have a traditional install with an Avstar Bendix and no fuel return lines. I do not want to run a line back to a tank or punch a fitting in one tank. Can I add a T onto one of the fuel lines before the valve?
Plane has been flying for over 5 years, so why stop adding things now…..

Thanks…….

 

[lr172]

I have a fuel return setup; Home made, not AFP. It draws from the servo input sump where strainer resides (doesn't affect FF readings, as cube is between servo and spider). Helps a bit with 100LL but helps a LOT with Mogas. I purge for a minute before a hot start and leave it open during taxi and run up. I am not sure that if you return it to a Tee in the line that you will be able to shed enough heat to be worthwhile. My speculation is that you will give up at least half of the benefit.

An idea to overcome this limitation is to put a valve on the return circuit. One output goes to L and the other R. Put the Tees upstream from the fuel selector. If you draw from L and return to R, then it works just like traditional fuel return, at least as far as temps go; Suck cool fuel from L tank and return hot fuel to R tank. Use caution if you do it like mine, as some valves can only handle pressure on one side of the valve and some valves are rated much lower than 30 PSI. A setup like mine requires careful engineering to insure it can't return more than what is left over from the pump flow in case it is left open at take off. Guessing this is not the case with the AFP setup.

Could also just tee into R or L upstream and always use the opposite tank for the feed.

Larry

 

[Auburntsts]

I have the AFP purge valve and I have it plumbed into the right tank line upstream of the fuel selector valve via a "T". And by upsteam I mean just a few inches from the valve. I'm sure I've got a pic or two but they're on my laptop at home so I'll have to wait and post until after I get off work.

 

[Kyle Boatright]

I have the AFP purge valve and I have it plumbed into the right tank line upstream of the fuel selector valve via a "T". And by upsteam I mean just a few inches from the valve. I'm sure I've got a pic or two but they're on my laptop at home so I'll have to wait and post until after I get off work.

Operationally, you return the hot fuel to the right tank (in Todd's case), but feed the engine off of the left tank...

 

[Auburntsts]

Operationally, you return the hot fuel to the right tank (in Todd's case), but feed the engine off of the left tank...

Correct. It took me some time via trial and error to figure out the right starting process (purge valve, throttle, mixture, fuel pump), but my cold and hot starts are total non-events. I'm convinced that every 540 has its own personality and what works for one will not automatically work for another despite being equipped exactly the same.

 

[togaflyer]

Yes if I do the install, I was thinking of a T on one tank’s fuel line, from the tank and before the fuel valve. So yes draw from one tank and return to the other. I definitely agree with Todd that the engines have their own personality, but the common is the hot start. I just want to make sure before spending time and money it is worth it. I hate doing lots of work for little reward.

 

[Walt]

Both engines I've had I ran FM200 with purge on the first, and even though my newer 370 came with the FM150, which technically doesn't need the purge valve, I installed it anyway. It lets you totally 'purge' the fuel lines of all that hot boiling fuel before you start so less stumbling/hard starts. If you have the typical sniffle valve it also prevents much of the overflow from that as it's no longer dumping fuel into the intake system after shutdown. Hot engines always are flooded as the fuel from the manifold pours into the cylinders (which is why most folks struggle with hot starts), the valve dumps all the fuel back into the fuel system where it belongs instead of into the cylinders.

 

[Auburntsts]

Yes if I do the install, I was thinking of a T on one tank’s fuel line, from the tank and before the fuel valve. So yes draw from one tank and return to the other. I definitely agree with Todd that the engines have their own personality, but the common is the hot start. I just want to make sure before spending time and money it is worth it. I hate doing lots of work for little reward.

So here's the pic I promised on how mine is plumbed with a T to the right tank feed line immediately below the fuel selector valve.

 

[planenutz]

I have the Purge Valve on my IO-360 and it appears to work well, but then I've operated a number of different injection systems and as long as you have your favourite hot starting procedure down pat, there is little to be concerned about. While I'm happy with the Purge Valve I have installed I'm not sure I would go to the trouble of retrofitting one, especially if you've not had any issues starting without it.

For hots starts I turn the pump on and purge the system while I assemble my harness. This probably takes a good 40 to 60 seconds, maybe? I'm not sure you need to purge for that long but its just a good way of doing something with the time while putting your seatbelts on. I then turn the pump off, close the purge valve, give the pump a 2 second burst and start with the mixture lean. Job done.

My purge line goes all the way back to the right tank with the rigid fuel line running parallel to the breather line along the side of the fuselage . I simply added another -4 bulkhead fitting to the inboard tank rib during construction. This guarantees no recirculation of the warm fuel. For controlling the Purge Valve I purchased a high quality locking push-pull control from McFarlane. The last thing you want is for that valve to move in operation.

If you want photos of the installation I have plenty, but its pretty self explanatory.

Just a side note - something I never considered during the build. If you are pulling the fuel from the left tank and your right tank is very full, then it will be even more full after purging. I now have a habit (and a decal on my fuel valve) of selecting right tank for purging so I can't overfill that tank. It's not a big issue, but there were a couple of occasions where I had topped off both tanks a bit too high and then flew a couple of legs where I used the purge valve. When I got back to base the right tank cap was weeping and when I investigated further (by removing the fuel cap) a few tablespoons of fuel disappeared back over the top of the wing. Lesson learned... twice. I'm a slow learner.

 

[togaflyer]

So how Todd did the plumbing would work for my needs. I have the AVSTAR system, so the flow divider inlet faces aft. I need to figure out how the purge valve would install or if I need to add a short line between the purge valve and divider. What part number and length of push pull cable is recommended.

 

[airguy]

I ran the purge valve with my Bendix fuel injection setup for quite a few hours before converting to SDS. It's a good device, it works. SDS is better.