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Gascolators, physics and Canada

kearney

Well Known Member
Canadian builders may be pleased to learn that:

"Ottawa TCCA HQ has agreed the requirement of the exemption for a “gascolator” can be met by a device that functions OR by a system that is designed to separate water and particulate contamination from fuel. "

This means that a gascolator "device" need not be installed if the fuel system will separate water and contaminants. This is of significance for RV builders who have high pressure fuel systems.

As gascolators in RVs will always be located higher than the lowest point in the fuel system (the tank outlet), they cannot remove water from fuel (pre-flight) unless the laws of physics are repealed and water flows uphill....

Also, the filter media in gascolators is small (a few square inches) and too coarse (110+ microns)to protect injectors.

The fuel tank drain and properly sized inline filters meet the requirements and are now deemed acceptable under either the Exemption to CAR 549 or CAR 549.

For me this was quite important as most gascolators cannot withstand the fuel pressures in systems with electronic fuel injection. No can it adequately protect the injectors from sediment fouling.
 
That’s great news Les,

Can you point us to the supporting documentation in case a local inspector “hasn’t got the memo”?

May we assume this rule is retroactive for flying aircraft previously inspected?

Bevan
 
I'm certainly pleased with this as it never made sense on EFI equipped low wing aircraft. Thanks for all your work in aid of getting them to see the light.
 
That’s great news Les,

Can you point us to the supporting documentation in case a local inspector “hasn’t got the memo”?

May we assume this rule is retroactive for flying aircraft previously inspected?

Bevan

Bevan

The quote above came from an email I received from TC yesterday. If you run into issues with MD-RA you can use the "dispute resolution" mechanism that MD-RA was required to publish after my inspection battle with them last year. You will find it on their home page. At least now we can go to the real regulatory authority - Transport Canada.

As to previously inspected aircraft, I am not qualified to opine on what you can or cannot do.

Just for clarity, my read of what Transport Canada requires is effective filtering and the ability to separate out water. In a high wing airframe, a gascolator may be the only option if fuel freely flows from the tank outlet down the firewall to the engine.

Cheers
 
As gascolators in RVs will always be located higher than the lowest point in the fuel system (the tank outlet), they cannot remove water from fuel (pre-flight) unless the laws of physics are repealed and water flows uphill....
Unless water in the tank on a previous flight was sucked up and carried to the gascolator, where it sat until the next flight.
 
Unless water in the tank on a previous flight was sucked up and carried to the gascolator, where it sat until the next flight.

Which may apply for Carb and (most) Mechanical FI systems - low volume fuel flows would collect water & retain it in the gascolator to some extent, plus what ever settles out in the bottom of the tanks.

Les is not suggesting gascolators are no longer useful or required in carb or mechanical fuel injection installations. He is just noting that TC now acknowledges that gascolators can be exempted if it is not workable in installations like EFI, as long as provisions are in place to purge water accumulated in the lowest location (tanks).

With Hi Volume / Hi Pressure full return EFI systems, the best pre-flight procedure would be to check for water accumulation at the tank drains. Later, as soon as the fuel pump is engaged, whatever small water accumulations in the system plumbing would immediately be purged back into the tank, diluted harmlessly in the (hopefully) many gallons of fuel there.

As a side note & yet to be tested, it's questionable how much water would be retained in a gascolator when continually subjected to a High Volume Full Flowing fuel stream, if the turbulent flow through the gascolator might mix & syphon what ever water was in the bowl and carry it back to the tank anyway.
 
Which may apply for Carb and (most) Mechanical FI systems - low volume fuel flows would collect water & retain it in the gascolator to some extent, plus what ever settles out in the bottom of the tanks.

Les is not suggesting gascolators are no longer useful or required in carb or mechanical fuel injection installations. He is just noting that TC now acknowledges that gascolators can be exempted if it is not workable in installations like EFI, as long as provisions are in place to purge water accumulated in the lowest location (tanks).

With Hi Volume / Hi Pressure full return EFI systems, the best pre-flight procedure would be to check for water accumulation at the tank drains. Later, as soon as the fuel pump is engaged, whatever small water accumulations in the system plumbing would immediately be purged back into the tank, diluted harmlessly in the (hopefully) many gallons of fuel there.

As a side note & yet to be tested, it's questionable how much water would be retained in a gascolator when continually subjected to a High Volume Full Flowing fuel stream, if the turbulent flow through the gascolator might mix & syphon what ever water was in the bowl and carry it back to the tank anyway.

Ralph - Exactly!!

By the way, I did the science on gascolator operation last weekend. I mixed 1 gal of avgas and a couple of cups of water. Shook it up and then ran it through an ACS "high pressure" gascolator. After running the full gal through the gascolator, it retained only a small amount of water. I repeated the experiment after letting the water settle out - same result. In any event, a gascolator holds only a trivial amount of water. The closed loop fuel system means any water is swept back into the tank and is mixed with fuel. It is not meant to be a gas/water fuel separator IMHO.
 
Ralph, I would like to know more details about how you did the test. Flow rate through gascolator is my main question. What type of gascolator (filter material) was used. For example, I use Andair gascolators which have a 75micron filter element which I believe is to help strip off the water. I would think flow rate has a lot to do with the success of that.

If the water is shaken up with the fuel as you say, then immediately put (pumped?) through a line to the gascolator, I can could see why the water may not seperate out. But is this a realistic scenario?. What we’re trying to avoid is a slug of water in the bottom of the tank making it’s way to the engine. The volume of the gascolator is to allow the water to seperate out as it passes through. The filter material helps to. All in theory anyway as I understand it.

Bevan
 
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Ralph, I would like to know more details about how you did the test. Flow rate through gascolator is my main question. What type of gascolator (filter material) was used. For example, I use Andair gascolators which have a 75micron filter element which I believe is to help strip off the water. I would think flow rate has a lot to do with the success of that.

If the water is shaken up with the fuel as you say, then immediately put (pumped?) through a line to the gascolator, I can could see why the water may not seperate out. But is this a realistic scenario?. What we’re trying to avoid is a slug of water in the bottom of the tank making it’s way to the engine. The volume of the gascolator is to allow the water to separate out as it passes through. The filter material helps to. All in theory anyway as I understand it.

Bevan

Hi Bevan

So there were two tests at about 34 GPH. The first had fuel mixed with water and shaken (not stirred per JB!). This simulated getting a partial tank of contaminated fuel. The second test allowed fuel to sit for 30 minutes and the water to settle out.

In both cases the gascolator collected minimal water. The filter media was about 6-7 square inches and 110_ microns. If you google fuel/water separators they have filters that are under 10 microns.

Gascolators are not fuel / water separators. What they do do is allow water to collect and be detected when located in the lowest part of the fuel system. They serve no purpose other than a fuel filter when installed in a low wing aircraft such as an RV. In my PA28 that I flew for 19 years, I only detected water when draining the tank and never in the FWF gascolator.

PS: Where are you located? I am in Springbank. We should meet sometime and swap lies.
 
What we’re trying to avoid is a slug of water in the bottom of the tank making it’s way to the engine.

Bevan

Draining the tanks before flight would eliminate this possibility.

With EFI systems and the high return fuel flow (99% return at idle), any water in the system is completely mixed with the fuel within a few minutes. 35-40 gph are typical pumping rates with these systems.
 
Les is not suggesting gascolators are no longer useful or required in carb or mechanical fuel injection installations. He is just noting that TC now acknowledges that gascolators can be exempted if it is not workable in installations like EFI, as long as provisions are in place to purge water accumulated in the lowest location (tanks).
Correct, and I got that, but his statement was generic and did not allow for the validity of a gascolator in non-high-pressure fuel injected systems, so I wanted to clarify.

As a side note & yet to be tested, it's questionable how much water would be retained in a gascolator when continually subjected to a High Volume Full Flowing fuel stream, if the turbulent flow through the gascolator might mix & syphon what ever water was in the bowl and carry it back to the tank anyway.
I don't claim to know the answer to this, but my understanding is that a gascolator operates centrifugally, ie. the gas enters at an angle and swirls inside the chamber before exiting at the filter in the middle. Would that swirling effect create enough G that the water would be preferentially pulled to the outer walls and therefore less likely to get to the filter in the middle? Thinking out loud here only.
 
Correct, and I got that, but his statement was generic and did not allow for the validity of a gascolator in non-high-pressure fuel injected systems, so I wanted to clarify.


I don't claim to know the answer to this, but my understanding is that a gascolator operates centrifugally, ie. the gas enters at an angle and swirls inside the chamber before exiting at the filter in the middle. Would that swirling effect create enough G that the water would be preferentially pulled to the outer walls and therefore less likely to get to the filter in the middle? Thinking out loud here only.

I don't believe there is a great deal of swirl in a gascolator. Gas in at the top and gas out at the top. I think it relies on dwell time and gravity to separate the water from the gas. The Usher gascolators I have seen have a screen (i.e. filter) at the top and nothing in the center of the cup. They have nothing engineered in them to establish any swirl, like you see inside of an air oil separator. Those also operate on a dwell time priniciple and not really centrifugal force. The swirling increases area and dwell time, as well as surface area exposure.

Larry
 
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I don't believe there is a great deal of swirl in a gascolator. Gas in at the top and gas out at the top. I think it relies on dwell time and gravity to separate the water from the gas. The Usher gascolators I have seen have a screen (i.e. filter) at the top and nothing in the center of the cup. They have nothing engineered in them to establish any swirl, like you see inside of an air oil separator. Those also operate on a dwell time priniciple and not really centrifugal force. The swirling increases area and dwell time, as well as surface area exposure.

Larry
Larry

You are correct. The two gascolators (ACS & Usher) that I have examined do not have a venturi effect. Also, the volumes of these devices is so small that the amount of water they could retain is trivial. The advantage of a gascolator located at the low point is that it would collect and retain standing water. Draining before flight would provide evidence of contamination (if any) before flight. Located anywhere else it would only function as fuel filter.

In a low wing aircraft, it is far more effective to drain water from the tank using the tank drain and have a properly sized in inline fuel filter (IMHO). Keep in mind that the gascolator filters are too coarse to protect fuel injection systems and are far smaller in surface area than inline filters.
 
Me
"Les is not suggesting gascolators are no longer useful or required in carb or mechanical fuel injection installations. He is just noting that TC now acknowledges that gascolators can be exempted if it is not workable in installations like EFI, as long as provisions are in place to purge water accumulated in the lowest location (tanks)."

Snowflake
"Correct, and I got that, but his statement was generic and did not allow for the validity of a gascolator in non-high-pressure fuel injecture systems, so I wanted to clarify."

...... "validity of a gascolator in non-high-pressure fuel injected systems"???
At no point did we question the "validity ..."
We (Les, Ross & I) would all agree that gascolators are appropriate for carb & mechanical FI systems!

Continue on with the endless gascolator debate if you must...
 
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I might add that we have hundreds of EFI equipped aircraft flying in the US without gascolators. No issues to date that I'm aware of.

The laws of physics are no different north of the 49th Parallel as far as I am aware...

Les did an actual bench test to prove or disprove the ability of a gascolator to remove useful amounts of water from a high flow, high pressure fuel system such as those used in EFI aircraft. It didn't, so it serves no useful purpose in these installations, outside of coarse filtering.
 
Mechanical FI systems - low volume fuel flows

Hi Volume / Hi Pressure full return EFI systems

I'm clearly uninformed on these two types of FI systems. Perhaps it's not too late to get smart(er). I have installed Andair gascolators in the wing roots and an Andair fuel boost pump. I have ordered a Lycoming IO-360 M1B. Am I describing a mechanical FI system or a Hi Volume / Hi Pressure full return EFI system?

Thanks
 
I'm clearly uninformed on these two types of FI systems. Perhaps it's not too late to get smart(er). I have installed Andair gascolators in the wing roots and an Andair fuel boost pump. I have ordered a Lycoming IO-360 M1B. Am I describing a mechanical FI system or a Hi Volume / Hi Pressure full return EFI system?

Thanks

Yours is a mechanical FI system with no tank return. Mechanical boost pump, mechanical engine driven pump, mechanical fuel servo and divider. The Hi Volume/Hi Pressure full return EFI system is an electronically controlled fuel injection system similar to a modern automobile with tank return.
 
"I have ordered a Lycoming IO-360 M1B. Am I describing a mechanical FI system or a Hi Volume / Hi Pressure full return EFI system?"

With a new Lycoming M1B from the factory, you most likely will be equipped with a mechanical FI set-up - unless you specifically asked to be equipped differently.
The following is basic differences of the plumbing between the most common fuel systems.
-Mechanical FI run on about 28 psi between the pumps and the servo, the max fuel flow would be the max amount your engine would burn, maybe about 14gph at wide open throttle at take off. So lets call that medium pressure/low volume.
-For comparison, if you had a Carburetor system that would be about 5 psi between the pump and carb, still the 14 gph at wide open throttle. So the carb system would be a low pressure/low volume.
-Electronic Fuel Injection systems are radically different in their plumbing compared to a mechanical set-up. Basically, fuel is drawn from the tank by an electric High Volume/High Pressure fuel pump and delivered directly to a fuel injector (electric servo valve)on each cylinder at up to 45 psi, and the pressure is maintained in this part of the plumbing circuit by a pressure regulator valve (to maintain the 45 psi) and what ever fuel that is not used is let through the regulator and sent back to the tank to eventually be re-circulated through the system again. To maintain these high pressures, the system has to operate at high fuel flow rates (up to 35 gph, again, only a small portion used, excess sent back to tank). The fuel injector servo pulses are controlled by an electronic control module programmed to act & deliver the right amount of fuel for each piston stroke.

The point of discussion on this thread is the appropriateness of installing a gascolator (controversy about it's ability to actually collect water, and inability to stay sealed) in an fuel plumbing environment involving the high pressure (up to 45 psi) and high flow volume (up to 35 gph) system.
 
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