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Ah, true on certain carbs. For example, on the MA-4-5 carb, the fuel inlet screen is not accessed through the fuel inlet, so no need to disconnect the fuel line.
I don’t know if all our carbs are like this, but on the ones that I’ve owned, I pull the carb inlet screen out from the side opposite the fuel line inlet. I think it can be pulled from either side. I might be wrong about that, but it’s the way I do it. Of course I don’t think that justifies using a hard line for the carb fuel inlet.
A failed fuel system in RV's And Rockets has cost lives.
+1
Misleading picture, sorry. That arrow points only to the fuel inlet side of this carb . Yes, the fuel would go through the screen, but that is not how you access it for inspection. The inlet screen is on the opposite side and not accessible from the inlet side. (Your arrow would be correct for an MA-3 carb, however.). So, to stay on point, a hardline would not make inspection on this carb more difficult.
I will admit that sticking with flexible hose is the easiest, most guaranteed, if not traditional method in this application. For me, this is just an out of the box thought experiment and question. I think some good points have been made for and against a hardline between pump and carb.
Yes. In my 40+ years in the aerospace industry, GA’s practice of using hoses in this application is the outlier by far. The vast majority use hardline as the default. Hose, being heavy, bulky, fragile and expensive, is reserved for those specialty cases where there is motion between components OR maintenance access drive it into consideration. Properly fabricated, engineered and installed hardline is proven to be the most elegant solution.
It is only rubber on one side. It is rigidly attached to the engine via the AN fitting, so will pick up any vibration from that engine. The rubber is not really isolating any vibration, just dealing with differential expansion rates in cyl vs CC; Al Tube is still vibrating.
As a fluidline supplier, hoses are about 90% of our product catalog. In this case, a stainless tube might acceptable, if it were supported, and whatever movement would not loosen the pump fitting. Good case for Michael's post is the stainless prop governor tubes. Also, on most turbine and rocket engines, there is a lack of hoses, except where airframe to engine connections are necessary. So YES, well planned rigid tubes are great. Well planned, is the key. As for FWF on experimentals, we recommend NOT using aluminum, especially 3003, due to its potential flare cracking behind the sleeve. 304 or 316 stainless works well.
Well -- I have an Marvel Schebler Model MA-4 on my O-320-D2A in my RV-9A -- same one. The screen is removed by removing the inlet port nut that holds the inlet fitting itself. The barrel fuel screen comes out with inlet port and fitting as shown below in mine. Been inspecting my fuel inlet screen for 22-years during the condition inspections. Photos of my carburetor on the bench to replace the "old style" plastic float with the new greatly improved blue epoxy float (#F update) back in 2016. BTW -- when you pull your fuel inlet port, it's also a good idea to replace that copper washer, too.
John, at the risk of getting burned by the flame war on the horizon, I'll answer this. Obviously a rigid tube has a smaller OD for the same ID as a hose. Sometimes a tighter bend radius, depending on the bend die thats used. In the above pic, the multiple bends will absorb any vibration and potential misalignment. It does take practice, patience and skill to make a custom rigid tube like that. That being said, most builders dont have the tools, practice, or time, and use teflon hoses. YES, teflon has a larger bend radius, especially with firesleeve. Yes, teflon is not life limited, and somewhat easier to use. I can tell you that making custom rigid tubes for installs from emails or non prototyped drawings is tough, and generally wasted time and expense. You never know if its going to fit, unless you are actually at the plane and do mockups. and you never know if there is something that will interfere with the tube. Pic below was Michael's I0540 circa 2018 with his stainless tube. Well designed, supported and fabricated. So, for most builders, teflon hose is the answer, but YES YMMV.
O 320's use MA4SPA
The O-320s I've worked on typically have "MA4" carbs. Are you sure you have an "MA-4-5" ? My O360 has an MA-4-5 and know that it conforms to the service manual!
Hardline is lower weight, lower volume, lower cost, and more durable. The degree of difficulty to “service the carb” can range from nothing to significant, and that factor - serviceability - is one of the things that can overcome the other advantages of hard lines. If your carb comes off often enough that the difference between one B nut or two B nuts is a factor, then flex hose starts to make sense.
MA-4 with the fuel screen on the fuel inlet side as shown in my photos above -- not the MA-3 as you suggested previously. Again Jose, what advantage are you hoping achieve by using aluminum or stainless steel tubing over PTFE hose for your carburetor fuel supply line?
MA-4 -- not the MA-3.
Correct -- the MA-4 model type -- not the MA-3 as Jose suggested.
My friend, you have mis-read the posts. No one suggested your engine had an MA-3. In fact, once you later mentioned you had an O-320 you were corrected in saying you had an MA-4-5. The MA-3 was mentioned much earlier as an example of one that had the inlet port and fuel screen on the same side as opposed to what you originally indicated in your original MA-4-5 labeled picture (post #10). BTW, thanks for quietly changing the picture which is now correct and also editing your later posts which seemed to confuse the MA-4-5 with the MA-4.
It's an MA-4 (typo was corrected). So, don't you think it's about time to get back to the intended thread topic guys?. And, I clearly demonstrated that my Lycoming carburetor (MA-4) and many others have the fuel screen on the fuel inlet port -- my picture clearly showed that -- correct? The actual point here -- not to split hairs -- right?
bravo
