O-540 Fuel pump

[zkelley2]

Is anyone that is running a carb'd O-540 running an engine driven fuel pump with it? I guess that is, has anyone found the standard fuel system unable to deliver the gph required by a flow test?

My doner engine came off a Comanche 250, a low wing and needed an engine driven and electric backup. I haven't seen many 540 installations without that, so I was just curious what people are doing.
The only high wings I can think of with 540's are maule's and they have engine and electric backups.
I'm obviously going to do my own flow test to the carb, but just want a baseline to start with.

[alaskabearhawk]

Rob Taylor is running an O-540E4B5 with an engine-driven fuel pump and an electric backup.

[Mark Goldberg]

The Lycoming on my 4 place came with an engine driven fuel pump. I kept it on and had to also install a back up pump to force fuel through engine driven pump should it fail. I have seen flow rates of 27-29 gph on gravity flow systems with the fuel valve on BOTH. Less fuel flow of around 25 gph with the valve on L or R. Mark

[swpilot3]

I don't have any fuel pumps on my O-540. What's not there can't fail! I was able to get the required gph during the fuel flow tests, but no more. If you are very careful with smooth bends and no 90* fittings in the fuel system and don't use a red cube fuel flow transducer (I used the gold cube), you'll end up achieving the required gph.

Here's my fuel flow test: http://azbearhawk.com/2018/02/25/fuel-flow-test/

[nichzimmerman]

Bobby, did you use 3/8" hose with a Bob gascolator? I'm aiming to have no pump requirement either but haven't been able to find many fuel systems that met spec. Any tips besides gradual bends?

[swpilot3]

Yes, I did use the 3/8" tubing and Bob's gascolator. Take special care to make sure everything is always continually moving downhill, don't let it go down, then back up. Low spots could trap water also. Use as few fittings as you can. Each fitting is a place to leak and causes drag. I used a very long tube for the aft fuel line that comes down from the tank makes a sweeping bend then goes forward to the Tee. You could use 1/2" tube and I bet that would help a lot!

[Battson]

My IO-540 is built up from an O-540 case with that same style of engine driven fuel pump (the wobble pump).
We got acceptable fuel flow results, the minimum acceptable flow is 125% of the required flow which is 112 L/hr (29 GPH).
Without the pump, I believe you need to see 150% of max flow which is more like 135 L/hr (35 GPH).

We actually had the pump fail lately, the pressure was steadily dropping over about 50 hours which gave a clear warning sign of the impending failure. It was a cheap and relatively easy fix.

Interestingly, the engine will run at cruise power with the fuel pressure as low as a few psi, but it wont run for long without the pump working at all, maybe five or ten seconds as the pressure bleeds down. The electric backup pump works perfectly though, as soon as you flick the switch the engine roars back into life without delay. The Lycoming manual for IO-540 engines says the fuel pressure redline is about 10 psi from memory, which is very conservative.

[zkelley2]

I'm leaving the carb on, at least for now. The min psi for the carb is .5 iirc, which gravity can provide. But ya, about 35gph is what is needed to the carb from gravity for no pump.

[zkelley2]

Is anyone running a low pressure facet pump for a backup? The commanche this engine was off of had the electric pump's fuel line t in after the engine driven and had a check valve to keep the engine driven fuel from going backwards through the electric pump.

I was thinking an easier installation would be a free flowing facet pump then a line to the engine driven diaphram pump then to the carb. Is this how people plumb this or does a failed engine driven pump block fuel from the electric pump?

[Aero_tango]

I do have a low pressure facet pump as a backup. My engine is an O-540 carb’d, with an engine driven pump as well.
Just to describe my full fuel system...from the fuel selector, then gascolator, then to the facet pump and check valve (in parallel with the facet pump), then to the flowscan fuel flow, pass thru the firewall, to the engine driven pump and finally to the carb.
The measured fuel flow thru that fuel system, without any pump running, with the wheel jacked to simulate max climb attitude, and with only 1.5 gal in each tank was only giving me 13.5 GPH !!!!
Same setup, but with the facet pump running, 31.6 GPH.
I do recommend to go with an engine driven pump and a facet pump.

Mike.

[Airplane3472]

Hello Mike - any chance you would share the part number of the Facet pump and check valve you used? And a couple of pictures of your setup would be great. I plan to use the same type of setup on my O-540. Thanks for the info.

[bearhawk2015]

I have a carbureted 540 and flew for several years with out a fuel pump. Then I decided to put in a fuel flow transducer and I figured I would need a fuel pump to get the fuel flow required. My plane is plumbed just like Aero_tango’s except no engine driven pump. I don’t remember what my freeflow fuel tests were but it was sufficient. I did a bunch of flight tests with the pump on and off and came to the conclusion that the elec fuel pump was not needed for my installation.

[swpilot3]

Those pumps and check valves do provide a lot of drag for the fuel. Without all that the fuel system works just fine as designed. Ironically, putting all the pumps and check valves in, requires a fuel pump to get the proper flow! Ha!

According to Bob, the bad part of the engine driven fuel pump is that when they fail, they don't allow any fuel flow.

[zkelley2]

Those pumps and check valves do provide a lot of drag for the fuel. Without all that the fuel system works just fine as designed. Ironically, putting all the pumps and check valves in, requires a fuel pump to get the proper flow! Ha!

According to Bob, the bad part of the engine driven fuel pump is that when they fail, they don't allow any fuel flow.

I was wondering that about the engine driven pump, and figured it was the case based upon how all the fuel systems seem to be set up, but couldn't find anything definitive.

[Mark Goldberg]

It is my understanding that an auxiliary boost pump does force fuel through the engine driven pump if it fails. Mark

[Battson]

It is my understanding that an auxiliary boost pump does force fuel through the engine driven pump if it fails. Mark

Yes that is definitely correct.

[zkelley2]

Found this today from Tempest. Answers all my questions on how they work.

https://www.youtube.com/watch?v=fxT4RAEssnw

[Aero_tango]

Hello Mike - any chance you would share the part number of the Facet pump and check valve you used? And a couple of pictures of your setup would be great. I plan to use the same type of setup on my O-540. Thanks for the info.

The check valve in an Andair check valve, available at Spruce. I don’t have the exact p/n, but if you looked them up, they are all the same, only the end fitting is different. You would want the “non-bleed” version.
As for the Facet pump, I’m pretty sure it’s the 40108 model, which is the same as Van’s sell for all carb’d engine.
Sorry I don’t have any good picture available. Mike