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engdavidj

Fuel Filter Purpose?

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What is the purpose of the 5/16" metal fuel filter? I believe both fuel tanks feed into a Y connector, flow thru the shutoff valve, thru the small 5/16" metal filter and then into the gascolator on my 2006 CTSW. The fuel drops into the large sediment bowel in the gascolator and then flows out of the top thru a very fine screen. The surface area of the GASCOLATOR SCREEN is MUCH LARGER than the small fuel filter screen. Solid debris would settle in the bottom of the sediment bowel.

I would think the small fuel filter screen would CLOG UP MUCH SOONER than the large gascolator screen, leading to fuel starvation and engine failure.

Which makes me wonder, WOULDN'T IT BE SAFER TO REMOVE THE SMALL METAL 5/16" FUEL FILTER?

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If that filter was not present, it may allow larger debris to plug or severely restrict fuel flow to the gascolator inlet.

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Isn't the inlet to the gascolator completely open as in having a diameter of at least 1/4"? Only the outlet is screened. The both wing tanks also have a course screen on their outlets. The picture is for another brand of gascolator I found on the net.

gascolatorA.jpg

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A friend who used to be in the fuel pump business call the inline filter a rock catcher. As Bill said, it can stop something that might get caught in the inlet fitting on the gascolator. 

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A "rock" would be caught in the fuel tanks with their course screens. Any smaller particles would be caught in the gascolator sediment bowel since the fuel enters thru the middle pipe which is huge. The man's finger is pointing to the inlet. Since the gascolator has a very fine screen nothing would get to the fuel pump. The outlet is just above the man's finger behind the screen.

 

On my 2006 CTSW my gascolator has THREE hoses. What is the third hose for? Are you saying the fuel goes from the small metal fuel filter, to the fuel pump FIRST and then to the gascolator?

CTSWfuelSystem.jpg

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Thanks Tom. I see what you are leading to. IF I had a fuel flow sensor I would need the small metal fuel filter to protect it. I don't, I am steam gauge.

 

Is it possible to connect the fuel flow sensor under the hood in the engine compartment? I would think locating fuel components OUTSIDE of the passenger compartment would be safer should any leaking occur. I can see where it is EASIER to locate and connect behind the dash board INSIDE the passenger compartment.

 

I am about ready to replace my small metal fuel filter with a simple piece of hose. NO MAINTENANCE and it is SAFER by increasing the amount of debris to clog the filter which would be only the gascolator.

 

The THIRD line on my factory 2006 CTSW gascolator. I am assuming that is either an overpressure relief accomplished with an orifice or some type of vapor return line that connects directly to the lower pressure gravity fed input. I have not been able to locate any documentation on the third gascolator line.

 

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Yes, the third line is for vapor return. 

If your airplane is registered as a SLSA, then you can not just remove the filter.

I often relocate the filter to above the fuel valve when doing a hose change. I use a fuel injection clamp at the firewall and "U" tube. This is where I disconnect to clean the filter. I also ancor the "Y" to the firewall. It makes removing the filter for cleaning much easier. You leave the lines connected to the filter. You do have to pinch the fuel lines to shut the fuel off, but that is easily done. Above the valve is allowable per the old SB requiring the change from the plastic filter to the metal filter.

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Thanks Tom. Sorry I should have clearly stated upfront that I am registered as ELSA. I am a new user to the group. Twice I tried to edit my "Profile" to add ELSA but it does not seem to take.

 

I still do not see any valve at all to the small fuel filter and actually now see it as a NEGATIVE since the small filter will clog much quicker than the gascolator. Why run a small filter DIRECTLY into a larger more capable filter?

 

Changing the factory design of the fuel system is something I do not take lightly, especially with a well engineered airplane. Thus the extensive discussions on the forum with other experienced users.

 

The Dynon installation instructions state there are no restrictions on the placement of the fuel flow sensor. In the engine compartment , after the fuel pump is ok. I would think the cleanest place is after the gascolator.

Dynon120FuelFlowSensor.jpg

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35 minutes ago, engdavidj said:

I still do not see any valve at all to the small fuel filter and actually now see it as a NEGATIVE since the small filter will clog much quicker than the gascolator. Why run a small filter DIRECTLY into a larger more capable filter?

 It is not about the size of the filter, but rather the the size of particulates the filter is designed to remove. The two filters are designed with different purposes in mind.

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After buying my ct it was my first complaint. The small filter is a choke point in the fuel system. You will never see this in certified aircraft, fine filters of larger surface area are found after the gascolator in fuel injected engines and coarse screens right at carburetors after the gascolators. If there is any significant trash generated prior to the small filter it will clog up the screen. I know everyone says they never see much in the screen but I would hate to be the first one that does. When the first incident happens because of this filter there will be an air worthiness directive, it's called Tombstone Legislation. Anyway that's just my opinion. 

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My 2006 CTSW factory gascolator has a very fine screen with a large surface area. I cannot image anything getting past the gascolator. Any heavy debris will fall into the sediment bowel.

 

I don't know the "Microns" spec for my gascolator screen, but it was very fine. Aircraft Spruce lists 120 Microns pn 10543-1and 74 Microns pn 05-03436. I wish I would have measured the OD and ID of my screen to know if these would fit.

 

What are the typical uses for 120 Micron vs. 74 Micron filter screens?

 

The Rotax 912 fuel pump has an INTERNAL non inspectable non replaceable fuel screen. Thank you Brian Carpenter of Rainbow Aviation for your EAA video where I captured this picture. That screen APPEARS to be fine not course.

 

After the fuel pump what filtering is needed? Only if the fuel line interior has disintegrated due to age. My 1996 SeaDoo PWC's carb screens did clog up due to the 18 year old fuel line which was not resistant to Ethanol.

 

What would be an example of anything getting thru the gascolator?

Rotax912FuelPumpFilter.jpg

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This is the inside of the Rotax 912 fuel pump. The cover was ground off to get access. The black part  on top with the screen is the internal fuel filter. Brian Carpenter of Rainbow Aviation has this video posted at EAA.

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Somewhere on this forum Roger Lee, I think, has pictures of how/where to relocate the filter and change the fuel lines behind the panel so changing this filter is easy. Probably as Tom outlined above.

As from the factory it was a pain.

 

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EngDavidj,

I have looked at the same configuration you have in your CTSW in another similarly configured CTSW and came to the same conclusion that you did.

Two fuel filters is not always better than one (for "this" configuration, with these filters).

Which is definitely not obvious during a first look. 

Using the screen out of the FD filter as shown below it looks like it is equivalent to a 250 micron screen that would let particles smaller than .010 inch diameter pass the filter.

For the gascolator, the screen is listed as 125 micron which would only let particles less than .005 inch diameter pass.

So a gascolator would catch all the particles that the inline filter would catch but, due to the much larger screen area of the gascolator compared to the inline filter it would catch the same debris as the inline filter and still be open when the inline filter would be blocked.

Other benefits: three less joints which could leak, and much easier to maintain every year.

Since the airplane I worked on was an SLSA it was completed per design.

Looks like your Experimental certification would allow you to improve the design (And yes redesigning a fuel system is not something to take lightly!)

Thanks for your post.

DABAero

CTSW_Inline_Fuel_Filter.jpg

Mesh_vs_Micron.JPG

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The ctsw fuel system is poorly designed.  On example is the "Y" fuel connection at the firewall, the single tube that goes through the firewall is smaller than the ID of the hose which goes to the fuel valve. The clamp has to be extremely tight to prevent a leak. The  next hose change I do, I intend to change the fuel distribution plumbing to an established standard found on certified aircraft. I fully understand that standards are reduced for LSA however fuel plumbing is not something I will cut corners on and it is not costly or hard to do. I could not imagine being at altitude and start smelling a strong odor of fuel.

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1 hour ago, Madhatter said:

The ctsw fuel system is poorly designed.  On example is the "Y" fuel connection at the firewall, the single tube that goes through the firewall is smaller than the ID of the hose which goes to the fuel valve. The clamp has to be extremely tight to prevent a leak. The  next hose change I do, I intend to change the fuel distribution plumbing to an established standard found on certified aircraft. I fully understand that standards are reduced for LSA however fuel plumbing is not something I will cut corners on and it is not costly or hard to do. I could not imagine being at altitude and start smelling a strong odor of fuel.

I have done probably 15 hose changes to date, and I have never had issues with the "Y" fitting at the firewall except when I tried to use the 5/16" Gates hose that some have suggested using. With the proper sized hose there has never been an issue.

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I have discussed this with Roger at length as well. The two left and right distribution tubes are a larger size, there is no reason for this. I have seen some complaints of leaks in this area. If you are aware of this then it can be dealt with, however some have problems with it. 

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25 minutes ago, Madhatter said:

I have discussed this with Roger at length as well. The two left and right distribution tubes are a larger size, there is no reason for this. I have seen some complaints of leaks in this area. If you are aware of this then it can be dealt with, however some have problems with it. 

The only time I've seen issues is when someone used the incorrect 5/16" fuel hose. The fitting will literally fall out of the 5/16" hose! 

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Tom, when you say "incorrect 5/16" hose" what do you mean?  Is there one particular manufacturer who makes a "tighter" I.D.  or is there a DIN (metric) hose that should be used here?  Wondering if F.D. would approve a MRA for CTSW SLSA to remove the fuel filter and modify the fuel lines as described by Madhatter?  This appears to be a safety improvement because it reduces the probability for fuel starvation and reduces the number of joints which reduces the probability of fuel leakage.  I think it would really reduce the occurrence of fuel starvation in the population of CT's because, in reality, many owners might skip having the filter inspected each conditional inspection due to it being such a PIA to do and instead rely on the fuel flow results as a determination of the filter's condition.

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For a fuel line having different barb diameters on the same fuel line is not the preferred method. 

The below fittings are a good example for the CTSW fuel line which runs from the straight firewall pass through fitting to the gascolator.

The 7.5 mm (.298 in. diameter) fuel hose fits nicely at the firewall but is very snug at the gascolator.

The gates 5/16" (.313 diameter) fit nice at the gascolator but is loose at the firewall. 

How about just making all the barb diameters one size and then use Teflon hoses per Rotax SI-912-022 ?

No more 5 year rubber replacements just yearly or 100 hour inspections of the hoses.

DABAero

  

Fuel Fittings.JPG

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Nice picture of the difference.  This has been discussed a lot in previous posts.  My vote would be to use DIN hose and make a tight fit at the gascolator.  Still would like to see if FD would approve the rework Madhatter suggests.

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1 hour ago, Runtoeat said:

Tom, when you say "incorrect 5/16" hose" what do you mean?  Is there one particular manufacturer who makes a "tighter" I.D.  or is there a DIN (metric) hose that should be used here?  Wondering if F.D. would approve a MRA for CTSW SLSA to remove the fuel filter and modify the fuel lines as described by Madhatter?  This appears to be a safety improvement because it reduces the probability for fuel starvation and reduces the number of joints which reduces the probability of fuel leakage.  I think it would really reduce the occurrence of fuel starvation in the population of CT's because, in reality, many owners might skip having the filter inspected each conditional inspection due to it being such a PIA to do and instead rely on the fuel flow results as a determination of the filter's condition.

The parts catalog calls for a DIN spec hose 7.5mm ID. This is what was supplied from the factory. Instead of paying $35 per meter of hose some have chose to use 5/16" Gates hose because it is cheaper. 5/16" hose is 7.9375 ID. This .4375mm difference is the difference between the fitting falling out of the end of the hose or not falling out. As far as the fittings being different sizes, that is not ideal. I treat it as permanent connections and connections that are designed to be removed for service. I have always tried to use the location of the smaller fittings to disconnect hoses for service. I used to remove the whole fuel valve/filter assembly from firewall to firewall to service the filter, because it was easier. I have now started relocating the fuel filter between the "Y" and the "U" shaped tubes. I leave the hose attached to the filter, and disconnect at the Y&U shaped tubes. I use a 13.5mm Norma clamp at these locations. This is the same fuel injection clamp that FD used OEM.

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