Part identification

[Aero-Nut]

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

[Anticept]

Post a photo.

[Tip]

My guess is the fuel pressure sensor but it would be on the discharge side of the pump.

[Aero-Nut]

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.

[FlyingMonkey]

It's the awesomeness injector.  All CTs require some way of getting all that awesome into such a small airplane.  

 

 

But seriously, yeah I have never heard of this kind of thing.  Definitely need a pic.

[Tom Baker]

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.

[IrishAl]

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.

[Anticept]

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.

[Tom Baker]

SW's do have the return line just like the LS.

[Aero-Nut]

^{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?}

[Aero-Nut]

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?

[Anticept]

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).

[Anticept]

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.

[Tom Baker]

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.

[FlyingMonkey]

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.

[Anticept]

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.

[Anticept]

So, what you're saying is semantically speaking, we shouldn't think of it as one

[IrishAl]

What does it damp?

[Tom Baker]

The companies documentation and location in the fuel system seem to indicate that it is to keep the fuel FLOW indicator steady. This may be because of the way the fuel recirculation is set up on the CT.

[Tom Baker]

I look at it this way. It dampens and they call it a dampener and doesn't accumulate.

 

I guess you can call it anything you want.

 

Fred works for me.   

 

A rose by any other name is still a rose.

[Doug G.]

A rose by any other name is still a rose.

It misquote only works up to a point. Tell your wife you are bringing home manure will probably elicit a different response than if you tell her you are bringing roses. ????

[Aero-Nut]

Fuel pressure pulsation so it doesn't show up on the instrument panel on your gauge. Newer instrumentation don't usually need this. These were on older models.

Should it not be on the side of the fuel pump that the fuel pressure sensor is located to smooth out the pulses? I am not an expert on fluid dynamics but.....

[Mike Koerner]

Here's a possible explanation of the upstream position: All pumps, need some minimum inlet pressure (suction head) to avoid cavitation. We have a gravity-fed fuel system to supply that pressure. However, gravity systems are sensitive to turbulence (g-loads). Any bumps that momentarily lighten the load on our butt will also reduce the pump inlet pressure... if not for this device which uses the gas pressure outside the bellows, acting on the tiny volume of fuel "accumulated" in the bellows, to maintain fuel pressure and flow at the pump inlet during these momentary interruptions (mind you, we are not talking about aerobatic flight or sustained negative g's). If you looked at a plot of the pump inlet pressure as a function time in turbulent conditions it would like like January's S&P 500. The dampener (also called a snubber) smooths the pressure out. This may be more of an issue for the flow meter than the pump.

Mike Koerner

[FredG]

Fred thinks it should be called "Bob".

[Tom Baker]

Should it not be on the side of the fuel pump that the fuel pressure sensor is located to smooth out the pulses? I am not an expert on fluid dynamics but.....

It is not there to smooth out fuel pressure, but to keep the fuel flow indication steady. My guess is that the fuel bypass introduces pulses from the pump back into the supply line at the gascolator, and the damper is there to keep those pulses from messing up the fuel flow.