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Vapor Lock?

Walt said:
I never had a problem starting mine, it was just the facet pump running fast and not pumping (sounded like a dry pump) that occured. After installing the purge valve it took just a few seconds or less of purge before you heard the pump slow down and start pumping again like normal. I sumised the fuel was boiling in the gascolator and fuel lines FWF and vapor pushed back to the pump and caused it to vapor lock, no where else for the vapor to go. Until you release the vapor pressure fwd of the pump either by running or by purging the situation would continue.
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I'm really close to agreeing with you on this Walt. I tried to force the condition this evening by flying over to Baytown for fuel (I've had the problem twice there, under the same conditions), but alas, all started just fine. Next time I get the fast running pump, I am going to try the primer valve, and see if that burps it.

Paul
 
Facet on firewall soaking heat

I remember one builder did some testing of the facet fuel pump a few years ago. He instrumented temperature sensors, and found that the firewall mounted (cabin side) fuel pump would get very hot. It would soak the heat from the firewall. He insulated the pump from the firewall, and then claimed that the fuel line temperatures decreased. Anyone remember this? Sounds like something to try.
 
Lycosaurus said:
I remember one builder did some testing of the facet fuel pump a few years ago. He instrumented temperature sensors, and found that the firewall mounted (cabin side) fuel pump would get very hot. It would soak the heat from the firewall. He insulated the pump from the firewall, and then claimed that the fuel line temperatures decreased. Anyone remember this? Sounds like something to try.
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Might be something to try for someone having a problem on a 9A, but as I mentioned in a couple of posts, this is on an -8, and the Facet pump is about 8 inches or so behind the firewall, mounted on the inside of the fuselage sidewall. The only FWF heat it can see is conducted through the fuel line itself....

Paul
 
My two cents

Paul, I believe your original question is "why now" and not the first 1000 hours.
If I remember correctly most of that first 1000 hours you had the airplane on an airport with fuel, so maybe you weren't doing so many quick turns at fuel stops? Also you noted how hot it has been lately, even one or two degrees C hotter and some 100LL at the bottom of the vapor pressure range could make a big difference.

If you are flying with cockpit temperatures hot enough to boil Avgas at sea level you are much more hardy man than I am. So I believe the heat source must be FWF. My idea is that the fuel is boiling under the cowl and in the float bowl. This forces the vapor back through the electric pump (maybe all of the way to the tank) causing it to lose prime. This coupled with an empty float bowl means no start up. What I would try is shutting off the fuel valve immediately after shut down to trap the vapors downstream of the Facet pump, when ready to start, turn the pump and fuel valve on at the same time. This should put pressure to the carb and refill the float chamber.

For what its worth.
 
Autogas and Vapor Lock

From my website posted 5/31/09:

A huge learning experience occurred recently with autogas....

After doing some formation training with the West Coast Ravens, I departed WVI heading north for Petaluma. As usual, I switched from 100LL (in the right tank) to autofuel (in the left tank) at the top of climb at 8500'. Shortly afterward the engine lost all power. I was completely surprised as nothing like this had ever happened in 1400 hours of flying this plane. Located over the Santa Cruz Mountains, I was not in gliding distance of anything pretty. I turned back toward the airport and switched back to the 100LL and power quickly returned. I circled over the airport and tried the autogas again. The engine ran perfectly. I decided that I had missed the tank detent and had starved the engine of fuel and proceeded to Petaluma normally on the autogas.

Upon arrival the cowl was removed and the fuel line disconnected. I used the electric fuel pump to time the filling of a container from each tank. Both the the 100LL and the autofuel tank filled the tank at an equal rate. Additionally the fuel tank vents were confirmed clear. This confirmed no blockage in the fuel system.

Fast forward to a hot day a few weeks later....

In the same scenario and a hot 90+ degree day, I departed TCY after more formation training and switched from 100LL to autogas at the top of climb. Just as before the engine lost all power. Unlike the last event, the element of surprise was gone and I was in gliding distance from a nice airport. I checked to see that the tank was selected correctly. It was. I looked at the fuel pressure, it was zero, and the addition of the electric fuel pump was no help. Power was restored promptly by switching back to the 100LL tank.

Still in gliding distance from a nice airport, I reselected autogas, watched the fuel pressure drop to zero (with the electric boost pump on) and subsequently the engine quit running again. Power was again restored by selecting the 100LL tank. I continued home on 100LL. Fifteen minutes of cruise flight later, I was over another nice airport at 4500'. Autogas was again selected, but this time the engine ran perfectly. I had new theory what was happening........

As soon as I was home I Googled "Vapor lock" and found this excellent Wiki article:

http://en.wikipedia.org/wiki/Vapor_lock

(check out the second to last paragraph)

I feel 99.9% sure that introducing autogas to a hot engine caused vapor lock and was the reason for all the problems. Why had it taken four years to discover this? Because I had never introduced autogas to a HOT engine. I had either done a single leg and the engine was not too hot, or had waited until the engine temperature had stabilized in cruise to introduce autogas.
 
In the early years of the RV's, vapor-lock problems with carb'd engines were problematic in the hot Texas area. One of the more prolific builders, Bob Bashear, who was also an Lyc engine guru, came up with a nice mod that used a small orfficed tee at the carb fuel line inlet that continously fed some of the inbound fuel back to the cockpit area fuel line. Thus operating the boost pump for a short time before starting would provide cooler fuel to the carb.

I was not an "RV convert" at that time as I flew a O-360 BD4. I would offen have similar problems and considered the mod. Although I never put the mod in and tested it, it would seem to be a interesting solution to consider as long as the system could provide an adequate fuel flow to the carb.

YMMV and I agree that all fuel system mods need to be handle very carefully and I do not recommend casual experimentation in this area.
 
I actually tried Bob's method before I went the purge valve route. The problem with this was I was unable to null out the reading on on my FF gauge using a .030 orifice (the same size I use on the transducers). Another benefit or the valve is to be able to rapidly flush the system rather than waiting much longer with the orifice method. Same theory as Bob's just using the purge valve in place of the orifice is the only difference.
 
Absolutely!

deene said:
YMMV and I agree that all fuel system mods need to be handle very carefully and I do not recommend casual experimentation in this area.
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Lots of accidents are caused by ill advised experimantation in this area. Vapour lock is a real phenominum and can have deadly consequences.

Having said that there are a couple of well proven alternative designs that eliminate the VL issue albeit at the expense of having to rely on the electrical system.

Frank
 
No new data points on which to work Alex - haven't found anything amiss in the system, and temperatures have cooled down, so it's going to be difficult to replicate if it is environmental (until next summer).

Paul
 
Vapor Lock???

Need some input,I flew last weekend and had this happen and it happen again this weekend. So here goes I live in Florida so temps are a little warmer, First takeoff, climb, leaning doesn,t seem to be any problem on Mogas. I run one tank Mogas the other Avgas. I also land on the Avgas tank to purge fuel system of Mogas. After landing I always open oil door. Then both times I was on the ground 3 to 4 hours. Now after startup on Avgas and run up takeoff no problem but on climb out I switched to mogas and then get Low Fuel PSI warning. Turn boost pump on PSI comes up but engine is still runnng ruff.
Lean a little to see if this helps, doesn't. Start to turn back to airport I had just passed, running that bad. Switched tanks back to Avgas while leaving boost pump on and in a minute engine smooths out turn boost pump off PSI steady,didn't touch a thing all the way home. So I read the VAF and think could this be vapor lock when I switched to the mogas on climb out with the engine hot? I have an RV-9A 0-320 Carb with firewall mounted fuel pump everything per plans, plumbing, gasolator. Maybe I should try to switch to Mogas after leveling off and things cool down in the engine compartment. What do Ya'll think?
 
mayo3808 said:
Need some input,I flew last weekend and had this happen and it happen again this weekend. So here goes I live in Florida so temps are a little warmer, First takeoff, climb, leaning doesn,t seem to be any problem on Mogas. I run one tank Mogas the other Avgas. I also land on the Avgas tank to purge fuel system of Mogas. After landing I always open oil door. Then both times I was on the ground 3 to 4 hours. Now after startup on Avgas and run up takeoff no problem but on climb out I switched to mogas and then get Low Fuel PSI warning. Turn boost pump on PSI comes up but engine is still runnng ruff.
Lean a little to see if this helps, doesn't. Start to turn back to airport I had just passed, running that bad. Switched tanks back to Avgas while leaving boost pump on and in a minute engine smooths out turn boost pump off PSI steady,didn't touch a thing all the way home. So I read the VAF and think could this be vapor lock when I switched to the mogas on climb out with the engine hot? I have an RV-9A 0-320 Carb with firewall mounted fuel pump everything per plans, plumbing, gasolator. Maybe I should try to switch to Mogas after leveling off and things cool down in the engine compartment. What do Ya'll think?
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It's that time of the year when winter blend mogas can cause trouble. The blend is different than in the summer season.

If you have a Hodges tester, check the vapor pressure of your mogas. I have found it most unacceptable this time of the year and drained it.
 
Paul,

Not to revive an old thread, but did you ever resolve this issue? Did "burping" the primer valve help?

I have the EXACT same issues as you where I beleive it is the FACET pump that is locked. It has occurred twice on me on quick turns in the heat.

Thanks,
Scott
7A
 
tx_jayhawk said:
Paul,

Not to revive an old thread, but did you ever resolve this issue? Did "burping" the primer valve help?

I have the EXACT same issues as you where I beleive it is the FACET pump that is locked. It has occurred twice on me on quick turns in the heat.

Thanks,
Scott
7A
Click to expand...

Actually, the weather got cooler, the problem went away, and I forgot about it. Now it is hot again, but I have removed my primer system, so can't burp the valve - lost that chance to give it a try.....:eek:
 
Last weekend I had my first bout of vapor lock in the RV-4, so I read this discussion looking for info.

90 hrs SN Lyc O-360 with carb, mags, standard fuel system with selector valve just fwd of the stick, Facet just downstream from there in the center tunnel about a foot forward of the spar, and the gascolator on the lower firewall.

It was in the 90?s, and I had about 90% 87 oct auto gas in both tanks, 10% 100LL. First time I ever had more than 50% auto gas. I recognized that this may be the perfect storm so was alert to the possibility of vapor lock (it was gassed up on a cool day, if I had filled it this day I would have used 100LL). It started and ran fine, flew for 20 min, then shut down for about 20 min. Normally it starts great with no prime even when hot, but it started hard the 2nd time. Fired up right away but spit and sputtered about 10 sec before it ran good. Taxied fine (mixture leaned as usual), did a runup to 1800 rpm, ran fine. Then had to wait a few minutes for the runway. On takeoff, mixture forward and as soon as I got to about half throttle it started sputtering so I aborted. Repeated the process and it did it again so I put it away.

After reading all these posts I have a few thoughts.

A number of you suspect the Facet pump is getting vapor locked and purging the line will help. First, be aware of this?

The fuel pump should be mounted with the outlet above the inlet. This will help with eliminate vapor lock issues. Never located the pump so the outlet is below the inlet. Horizontal mounting will not effect fuel delievery performance. http://www.facet-purolator.com/index.php?option=com_content&task=view&id=12&Itemid=83​

Mine is mounted horizontal with respect to the airframe, but it?s a tail dragger so the outlet is higher than the inlet at least on the ground.

Second, rather than running another line and a purge valve (I prefer KISS), how about turning on the pump and draining some gas out of the gascolator to fill the line, pump, and gascolator with ?cool? fuel. Not sure how much volume you need to drain, but it can be dumped back into the tank or a lawnmower if clean.

Third, if heat is the culprit I?d like to add some cool. I got a fuel pump shroud but never installed it because it looks like a major job with all the junk in the way. Thought about putting blast tubes on the pump but had another idea? add a NACA inlet or slotted louver on the top of the cowling between the rear baffle and firewall. This would/might bring ambient air down across the rear of the engine and exit out the bottom. It should cool the entire rear engine compartment better? all the accessories, fuel lines, firewall. In addition, when you shut down the heat back there has a place to get out and you should have a flow of cool air entering the bottom opening and exiting the top. Negatives: Drag? Water? (electrical stuff on the firewall and soon to be installed dual P-Mags probably should not get wet). Thoughts anyone?
 
Let's not re-invent the wheel

Fellas:

Experimental folks have been working with MOGAS for quite a while now - before MOGAS STCs were developed. I recall a tip from a fella I learned about in the 80s - he installed a tee at the carb fuel inlet and ran a line back to the tank. A .040 orfice at the tee kept the FP high enough, abut allowed any bubbles to go back to the tank. I do not recall if the tee has to be clocked so the return line was 'up' or not, but it might be a good idea. I expect this worked more or less as a purge system, but it was 'pilot-proof' as it required no input from the operator.

My guess is that the vapor line could be run into the selector valve with the same results.

Carry on!
Mark
 
Mark,
I have used this very system in my 8 although fuel injected.
The idea behind the constant return fuel line is a constant flow of cool fuel
to the fuel pump as well as an escape for vapor bubbles.
The T can be installed at the carb inlet or at the fuel pump outlet with the same result.
A # 40 hole seems a little large, on mine I drilled a #68 and tested it at 25 psi
where it would return exactly 9 gallons per hour.
You are correct in saying that it does not need any pilot input, however if you plan on using mogas in one tank and 110LL in the other you probably want to return gas to the same tank where the fuel came from so as not to dilute your 100LL.
Andair makes a valve for just this purpose or you can solve that problem with a separate return valve.
I have never had a sputtering or rough running engine on the ground or in the air and I believe it is because of this return line.
The installation adds a little complexity and requires accurate fuel gauges to keep track of the fuel quantity but it also adds a few options to fuel management.
 
vapor lock persists

I'd been having vapor lock in warm weather with a carbureted O-360 in my -7A, so during the condition inspection, I put an extra layer of firesleeve on the fuel line from the red cube flow sensor (on the left side of the firewall) to the carb (24"). Also put fiberfrax on the two exhaust heat shields nearest the fuel line. After leaving the engine off for 15 minutes after a brake conditioning run down the runway, it was very hard to start, even with boost pump on. I wonder if the extra layer of firesleeve just made it worse by insulating a cooked fuel line.
 
I got to looking at my gascolator and its distance from the exhaust pipe. Decided to put a heat shield on the gascolator. It may be a bigger source of vapor lock than the engine driven fuel pump, and people fit them with heat shields and blast tubes.
 
I did 1 hour flight to Tucson on Sunday with my RV7 O-360 fresh 100LL . It was a mere 101 degrees parked in the sun.

I went into the FBO for a half an hour.
I had **** of time starting the engine.

I tried a normal start several times and it would not catch.
Normal warm start is just crank it with a small amount of throttle.

The engine finally started to catch with a lot of throttle pumping. I had to keep pumping the the throttle for some time until it started run smoothly.
The boost pump was extra loud during the start too. I usually turn it on for a cold start only.

Does this sound like vapor lock ?
 
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