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How best to permanetly remove a fuel pump

d_kandle

FRIEND
Idaho
I am getting ready to test fly an SQ2 with an O-360. The engine is new and from Aero Sport. It has a mechanical fuel pump installed. I see many posts and advice from others that say I should remove that pump and just use gravity feed. I'll be ordering a cover so I can remove the pump and cover the hole. But, is it OK for awhile to just have no fuel passing through it but leave it on the engine? Can something bad happen by operating it dry?
 
Drill a piece of 1/4" aluminum to fit the bolt holes. Rough shape it and put a fuel pump gasket on it. It doesn't need to be fancy. But I wouldn't run a new fuel pump dry. Just me.

Web
 
I found a free flow one way check valve from ACS. Zero drop over the check valve. So I think I'll just add a bypass path with the check valve in it so if the pump output is less than head pressure the fuel will flow around the pump.
 
If the check valve truly has zero drop this should allow the fuel to keep flowing in the event of a pump failure. Personally I would remove the pump for weight savings, but that's just me.
 
First of all an 0-360 on a high wing (tanks in wing) airplane should run just fine on gravity fuel pressure. You should first check with Aero Sport to learn if the carburetor float level was set with a higher pump pressure than would be available by gravity. If so you may need to reset the float level. Other than that do as Web suggests.
 
I believe that the mechanical fuel pump on the front of a small bore continental Cont O-300 is driven by a lobe on the cam. But as I recall the mechanical fuel pump on the back of a Lycoming is driven by an internal lever or arm-- if you remove the fuel pump but leave that arm in place, it will flail around and cause some damage. I think you'd need to open the accessory case up and remove that drive for the fuel pump- not just cover plate it. I may be wrong, but I just can't remember how that pump drive works.
 
Just curious. Why do you think you need a fuel pump on a high wing aircraft? Even if it were aerobatic rated, this would be a poor choice of pump for the application. This type of pump is found on low wing aircraft that do not generate head pressure at the carb inlet. Warrior series aircraft always have a pump. Cub types never have a pump. No need to overthink a simple system.

Web
 
Just curious. Why do you think you need a fuel pump on a high wing aircraft?.....

I'm not saying that it applies in this case, but I've sen fuel pumps on high-wing airplanes. The 1948 C170 has an engine-driven pump, required due to fueline routing and the possibility of an airlock in certain situations- even though I know at least one person who never had a fuel pump on his in 32 years of ownership.

My 150hp C150 had an engine-driven fuel pump per the O-320 STC. Not sure why, but I assume due to fuel line size. Not sure if the 180hp Cub STC's require a fuel pump for the same reason or not.
 
Never have seen one on a Cub type aircraft, even the 180 hp conversions. The Cessna stuff sounds like the usual case of FAA 'engineering'.

Web
 
....as I recall the mechanical fuel pump on the back of a Lycoming is driven by an internal lever or arm-- if you remove the fuel pump but leave that arm in place, it will flail around and cause some damage.......

Did a little research...the diaphragm-type fuel pump on a Lycoming is driven by a vertical pushrod which is in turn driven off a lobe on one of the idler gears inside the accessory case. As I recall, the pushrod comes down to push on the top of the fuel pump arm & is returned up by the spring in the fuel pump. Not sure if the pushrod drops down far enough with the fuel pump removed to keep from being clattered up and down, but personally I wouldn't want it flopping around in there.
 
..... Not sure if the pushrod drops down far enough with the fuel pump removed to keep from being clattered up and down, but personally I wouldn't want it flopping around in there.
The rod will drop down away from the lobe and do no harm just resting out of the way. It has a mushroom on the top and will not fall out without removing the accessory case. Take off the pump, cover the hole and forget about it.
 
The rod will drop down away from the lobe and do no harm just resting out of the way. It has a mushroom on the top and will not fall out without removing the accessory case. Take off the pump, cover the hole and forget about it.

It'll drop down out of the way, but personally I wouldn't want to worry about hitting some turbulence or pulling a little negative G and having that pushrod bounce up and slam into the lobe on the idler gear. IMHO it's better to pull the acc case & remove that pushrod.
 
I am getting ready to test fly an SQ2 with an O-360. The engine is new and from Aero Sport. It has a mechanical fuel pump installed. I see many posts and advice from others that say I should remove that pump and just use gravity feed. I'll be ordering a cover so I can remove the pump and cover the hole. But, is it OK for awhile to just have no fuel passing through it but leave it on the engine? Can something bad happen by operating it dry?

I know this is an old thread but I’d like to hear what you ended up doing. Tempest makes different versions of engine driven fuel pumps with different outlet pressures, and FWIW Supercubs with 135 and 150 hp are on the AML. With experimental fuel systems I’m not sure a low pressure fuel pump would be a bad idea. Obviously you wouldn’t want a 30psi pump feeding a carb but a 4 psi pump feeding a modded engine makes some sense. I’m a bit surprised at the comments made in this old thread.
 
With experimental fuel systems I’m not sure a low pressure fuel pump would be a bad idea.
I removed the pump and put the Lycoming cover over the opening. When I did the fuel flow tests (125% of max flow rate) it didn't pass with the pump installed (and not moving). I got more than 125% max rate with pump not in the fuel path. I know that the normal failure mode of a pump is a failure of one of the diaphragms (and that normally just results in leakage from the inter diaphragm vent tube). If it were to stop moving in flight the engine would fail due to lack of fuel (very little fuel flowed with the engine off). It seemed that removing the pump made the engine more reliable.
 
Sound reasoning. I'm surprised the pump was that restrictive. Did Aerosport ever comment on why they installed it? With guys adding snorkel caps to pressurize their systems a low pressure engine-driven pump sounds like a reasonable alternative.
 
I removed the pump and put the Lycoming cover over the opening. When I did the fuel flow tests (125% of max flow rate) it didn't pass with the pump installed (and not moving). I got more than 125% max rate with pump not in the fuel path. I know that the normal failure mode of a pump is a failure of one of the diaphragms (and that normally just results in leakage from the inter diaphragm vent tube). If it were to stop moving in flight the engine would fail due to lack of fuel (very little fuel flowed with the engine off). It seemed that removing the pump made the engine more reliable.

At least in certificated aircraft, an engine driven fuel pump must be backed up by an “auxiliary” pump, generally an electric pump.

The Avcon engine conversions to install an O 360 in a Cessna 170 required an engine driven pump with a backup electric pump. Fred Dyen, a mechanic who taught A and P classes at the U did some research and found that this configuration was required because the size of the fuel line from the selector to the gascolator (I think) was too small a diameter to meet flow requirements for that engine at max power. In those systems, you are supposed to energize the electric pump during “critical” maneuvers (landing or takeoff) where max power might be required. If the mechanical pump shot craps right after takeoff.....bad day at Black Rock.

Fred got a few field approvals to replace that section of line with bigger diameter and removed both pumps. He offered to get a FA for mine, but never took him up on it.

My current 175 with O 360 has the same setup. Seems weird, since the original engine was 170 hp....but maybe Avcon just took the easy route. Would be interesting to see if you could get it removed.

But, there’s no way I’d operate an airplane with an engine driven fuel pump and no backup pump.

MTV
 
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