FUEL FILTER

[Austintatious]

I'm not sure why the most simple of questions is so difficult to find answers to sometimes, so I'll bug all of you!

There is 0 mention of fuel filters in the M20k manual.  0 search results for "fuel filter" here on mooney space.

A google search for "Mooney fuel filter"  yields a ton of results for OIL filters.....

I simply want to know how often the Fuel filter needs to be changed...  I assumed it was to be done every annual, but I am not sure the shop did so.

 

84 M20k Rocket

[MikeOH]

Showing my ignorance here, but is there a fuel filter?  I know nothing about 305 Rockets, but I'm pretty sure my M20F only has fuel screens that are suppose to be checked/cleaned, but I'm not aware of a replaceable filter (e.g. paper pleat, foam, or?).

[Austintatious]

2 hours ago, MikeOH said:

Showing my ignorance here, but is there a fuel filter?  I know nothing about 305 Rockets, but I'm pretty sure my M20F only has fuel screens that are suppose to be checked/cleaned, but I'm not aware of a replaceable filter (e.g. paper pleat, foam, or?).

Well, I am confused on this too... I know there are screens, but during test runs after an annual we found a completely clogged injector...  Given how small the orifices are I cannot imagine there is not a pleated fuel filter in this system somewhere... For crying out loud, we have that on even the crummiest boat engine setup.

[EricJ]

17 hours ago, Austintatious said:

Well, I am confused on this too... I know there are screens, but during test runs after an annual we found a completely clogged injector...  Given how small the orifices are I cannot imagine there is not a pleated fuel filter in this system somewhere... For crying out loud, we have that on even the crummiest boat engine setup.

Nope, just screens.    The final screens in the fuel system are very fine, though, and stuff has to be pretty small to get through.   Sometimes the stuff that clogs the injectors is from deteriorating seals and hoses past the filter.

[Austintatious]

1 hour ago, EricJ said:

Nope, just screens.    The final screens in the fuel system are very fine, though, and stuff has to be pretty small to get through.   Sometimes the stuff that clogs the injectors is from deteriorating seals and hoses past the filter.

Wow, that seems like pure insanity.

[N201MKTurbo]

9 minutes ago, Austintatious said:

Wow, that seems like pure insanity.

Where would you put the filter?

[Austintatious]

23 minutes ago, N201MKTurbo said:

Where would you put the filter?

In a nutshell, as far down the line as possible before the injectors.  In my other aircraft, I have 2 inline filters right before the carbs and a third filter as the fuel comes out of the tank. They all get changed every annual and they filter down to the micron level.

[N201MKTurbo]

10 minutes ago, Austintatious said:

In a nutshell, as far down the line as possible before the injectors.  In my other aircraft, I have 2 inline filters right before the carbs and a third filter as the fuel comes out of the tank. They all get changed every annual and they filter down to the micron level.

I think the theory is that fuel filters can clog, so more isn't necessarily better. Any particles smaller than the injector nozzles will just blow through the engine. The injector nozzles are 0.028" That is a good sized particle. 

The Mooney/Lycoming/Continental fuel screens are required to be inspected and cleaned every annual. The finger screens, which are at the inlet for the injectors look like they would stop anything bigger than 100 micron (0.004"). So the only place to pick up anything that could clog the injectors must come from the injector servo or the hose from the servo to the divider. Your inline filters wouldn't help with that.

It has been this way for a long time. I don't hear about a lot of problems because of it.

[EricJ]

2 hours ago, Austintatious said:

Wow, that seems like pure insanity.

It's actually very well engineered.    The "screens" trap more than many other filter media do.    The next time the finger filter in your system is removed for inspection take a look at it.   It will generally last the life of the servo (or longer, I suspect the screens will outlast the motor), and they filter down to much finer particles than will clog the injectors.   They are easy to clean out if they do accumulate some crap and are 100% reusable.

On most Mooneys there are one or two more screens along the way before you ever get to the finger filter.   So the finger filter only sees stuff that comes along past those, at the gascolator and sometimes also at the boost pump.

It's a very well designed system.   Many airplanes are built the same way.

 

[PT20J]

According to the Precision Airmotive RSA operation and service manual, the most common inlet screen filters down to 74 microns. An average human hair diameter is about 100 microns.

When examining and cleaning these, remember that the screen filters from the inside out so debris will be inside the screen. 

[outermarker]

Wasn't there a mention of placing a fuel filter by the Duke fuel pump?

[47U]

44 minutes ago, outermarker said:

Wasn't there a mention of placing a fuel filter by the Duke fuel pump?

This one?

https://www.mooney.com/wp-content/uploads/2020/12/SBM20-222B.pdf

[ArtVandelay]

Wasn't there a mention of placing a fuel filter by the Duke fuel pump?

It’s a screen, when I removed the fuel pump to be overhauled, the screen was clean, so I assume the pickup screens are doing their job.