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Part identification


Aero-Nut

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I removed my upper cowl today and say a part installed in the fuel supply line to the fuel pump. It appears to be some type of expansion tank about the size of a golf ball. What is this? I have never seen anything like it on any other 912.

 

Ken

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Has no wires. Just a "T" fitting inline with a bulb on it about the size of a golf ball. It is on the supply line. Basically appears to be an accumulator of some type. Why on the low pressure side I don't know. I will get a picture today.

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This is a fun one.

 

This is a fuel pressure pulsation dampener. It is on the pressure side of the fuel pump and because of pulsations in the fuel line (due to the diaphragm in the pump) this BULB has a metal bellows inside which dampens the fuel pressure pulsations and keeps the fuel pressure on your gauge steady and not pulsating. These have been around since 2006 with the introduction of the Dynon's.

post-3-0-68457000-1453992177_thumb.jpg

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Like Roger said these have been around for a while on CTSW's with the factory Dynon D-120 EMS. I have to disagree on them being installed on the pressure side though. I have always seen them installed on the inlet side of the pump on the CTSW's. It doesn't make much sense to me with where they put them, but when doing a hose change I always put them back in the same spot if installed.

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Pulse dampeners were designed for use on injection systems, which operate at high pressure.  They dampen the shock wave created by the sudden opening and closing of the injectors against the high pressure fuel, and they are designed to prevent excessive strain/wear/failure of the injection system.

 

I suspect they would make little or no difference in a low pressure carb system.

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If what Roger posts is it, then yes Aero-Nut, it's an accumulator!

 

Do SWs not have a fuel return line to the gascolator?

 

Anyways, there's one potential reason I could see with using an accumulator on the INLET side of the pump, and that's to prevent vapor from forming in the line when the pump diaphragm retracts. However, it still doesn't  really make sense in our low pressure carb systems and especially with how huge the hoses are (they can flow 20+ gph) compared to how little the airplanes use.

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Wow... Weirdest thing I have seen on a Rotax motor.. lol No it says: "This extremely simple device is incredible effective at reducing the fuel flow reading fluctuations common in turbine transducer-based electronic instrument installations" So why would it be on the opposite side of the fuel pump. I would assume there will be a lot more pulsing happening on the pressure side where the fuel pressure transducer is located?

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It isn't an accumulator. It has a bellows inside to dampen pulses.   http://www.matronics.com/fuelchec/damper.html

 

It looks like this inside.

 

http://www.flexicraft.com/Hydropad_Accumulator/Pulsation_Dampener/?gclid=CJf0rqv1zcoCFQVbfgodAxgEvg

 

That's an accumulator. Smoothing pulsations is one of the things an accumulator does. When pressure in the line rises, the air compresses on the other side of the bellows, and when pressure falls, the energy stored in the compressed air is released back into the system. What you're showing me is one of the types of accumulators used in aircraft hydraulic systems. They can call it a dampener all the want, but that's one of the purposes of an accumulator :-)

 

Wikipedia: "An accumulator enables a hydraulic system to cope with extremes of demand using a less powerful pump, to respond more quickly to a temporary demand, and to smooth out pulsations. It is a type of energy storage device." Yes, I linked a hydraulic article, but changing the fluid doesn't change the physics :-).

 

These types of devices are also used in the oil fracking industry. A high pressure diaphragm pump is used to move drilling mud. The mud must not stop flowing or it can seize the drilling equipment. So they use many of these accumulators like the one you showed (but scaled up significantly and with a diaphragm).

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And on the inlet side I would guess there is not really a pulse per say... A negative one in pressure maybe but not positive?

 

Don't forget head pressure. That's a positive pressure that could theoretically inflate one of these devices. Still doesn't make sense though, as it looks crazy small and probably useless on the inlet side as it wouldn't be able to store much at all.

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This bulb has no storage space inside. It only has a metallic bellows. It accumulates nothing. The bellows expands and contracts.

 

 

An accumulator is a storage device first and MAY dampen during that process.

 

An accumulator doesn't have a bellows inside. An accumulator is usually meant for some type of storage. An accumulator can buffer pulses depending on its use, but it is usually meant to store some type of volume first. I used them in my dive compressor business. It was used to add a buffer to an air flow that was more demanding than the compressor put out. A storage tank on a compressor is an accumulator because the compressor may not be able to keep up from a straight feed so the filled tank becomes and a buffer zone, an accumulator.

 

Accumulator may refer to:

 

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Roger, The metallic bellows is the storage space. It accumulates fluid inside the bellows which compresses against the static pressure of the bulb interior. When pressure of the fluid builds up it compresses the static air storing that energy until it is needed due to a lower pressure then it pushes the fluid back out.

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I would guess a "true" accumulator is meant to provide a volume to ensure proper continuous pressure to a component in spite of any pressure drops due to pulses in the system.  This design, while it might have some small volume in it, seems designed to just even out what instrumentation sees by taking up the pressure spikes in the line.

 

But I don't have experience here, so maybe they are the same thing.

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We're comparing elecyrolytic capacitors to tantalum capacitors. They are all still capacitors, despite the fact a tantalum capacitors can't even store a revolutions' worth of hamster wheel energy. This little bellows is the same, it takes up a physical volume of fuel in the bellows, compressing the air and storing energy, just not much. It wouldn't be possible to dampen anything if it couldn't take up and release energy. That's a textbook definition and the very basic principles of an accumulator :)

 

There are also water systems that use small devices like this to prevent the water hammer effect from bursting pipes. They only exist to smooth the surge.

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"Roger, The metallic bellows is the storage space."

 

The bellows isn't placed in the bulb for storage of volume. Yes it has space in it, but not to function as an accumulator as we think of them.  If you think like that then the Bourdon tube in a pressure gauge is an accumulator.

The bellows has to hold some fluid to function, but isn't storing fluid for the engine, pump or system. It doesn't need an accumulation of fluid, but just enough for it to function. 

If you think along your lines too then anything that holds anything is an accumulator. Accumulators usually have a specific function for a given system. 

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