Fuel filter question

[ILikePike]

The Vans recommended/supplied airflow performance fuel filter is a 125 micron filter. The Precision Airmotive Silver hawk information for the fuel injection system provided with the Van's YIO-360-M1B calls for input fuel to be filtered to 32 micron. What's up with that! Any suggestions?

[rzbill]

Worry not.
The filter from Don at Airflow is fine. He knows what he is doing.

There is an integral filter in the silver hawk too. It is so fine that one can barely see light shine through it. (dark room and flashlight right on the screen) This filter is on the pressure side of the fuel system. Not sure I would recommend this fine of a filter on the non-pressure side of the fuel system.

[terrye]

I went through this too. When I discussed it with Precision Airmotive, they replied as follows:
"We recommend a nominal 32 micron filter because the finger screen in the inlet of the servo is 70 micron and is not meant to be a primary filter. I agree that most certified aircraft should have a similar filter installed, but I have no way of knowing what they use as they are separated from us by the engine manufacturer which gives engine installation specs. Also from our experience, most do not use a sufficiently fine filter".

It's also worth noting that the finger screen in the inlet of the servo does have a bypass, and so if it gets clogged with 70 micron particles, it bypasses and lets any contamination downstream through to the spider and nozzles.

After a LOT of investigation of certified aircraft fuel systems, and available components I ended up with the following system.
Andair GAS375 gascolators (70 micron) in each wingroot
Andair fuel tank selector valve
Weldon 18000A high pressure fuel pump mounted in the usual place ahead of the selector valve in the tunnel
Falls Filtration 02W05847 main filter mounted approximately where the Van's gascolator for a carb engine is mounted right side low forward of the fireeall. This particular filter is normally used on the Beech King Air.

The specs on the filter are:
Fluid: Avgas or Jet Fuel
Flow Rate: 600 pph, using Jet fuel this works out to 85 GPH
Pressure rating:
-Operating 75 psi
-Proof 150 psi
-Burst 225 psi
Filtration:
-17 micron nominal
-33 micron absolute
Pressure drop: 0.5 psi max at rated flow
Bypass valve cracking pressure: 1.8-2.2 psi

I think most FBO fuel systems have 32 micron or better filtration, but as protection against those that don't or for fueling from a drum I prefer to have an adequate main fuel filter with good contaminant filtration and dirt holding capacity. YMMV
I'm still working on mounting all this stuff and sorry do not have pix.

[ILikePike]

Interesting, anybody else got an opinion? What size particle will clog an injector if it goes past the bypass? I am concerned about making a mess in the cockpit removing the fuel filter for inspection. I would prefer it to be more convenient. This just gives me more concern about the Vans recommended filter but I am very hesitant to monkey with the fuel system.

[Walt]

My opinion... I would be more concerned about sucking hot fuel through a very fine filter (vapor lock) than I would be with injector clogging. The former can really ruin your day, the latter is more of an inconvenience.

A very fine filter should only be downstream of the fuel pump.

Fuel components (like large filters and gascolators) FWF act as heat sinks which promote vapor lock.

I use a large capacity 74 micron filter after the selector, I would not be comfortable with anything finer in the suction line.

Lot of airplanes flying with the AFP setup, very few problems.

Last but not least, "making a mess" is what happens when one performs maintenance, if you're afraid of making a mess, then let someone else do it!

[Bevan]

I just went through this...

My configuration is...
RV7A
O-360 converted to injection with SilverHawk

Canada requires a gascolator even with fuel injection but I didn't want it on the firewall per Vans instructions for carbed engines due to heat sink/vapor lock issues. So I put one in each wing root instead. Since these gascolators have a large 75 micron filter included, I removed the AP pre-filter which was located next to the boost pump. This was removed because it was now redundant being 125 micron, inside the cockpit possibly making it more messy/difficult to clean/inspect, and it's removal offset the additional weight of the second gascolator.

I later found that the Silverhawk required a "32 micron" filter either immediately before or after the mechanical fuel pump according to the manufacturer of the Silverhawk. In discussions with the manufacturer, it was determined that a 40 micron filter would be sufficient since 32 micron isnt available, and 25 micron is unnecesary. The smallest dimention that could be affected by debris is approximately 70 micron if I recall.

I found a 40 micron filter that fit inside the AP filter housing and will mount it downstream of both pumps on the firewall. It will have a large piece of firesleeve covering it for heat protection. I don't expect to ever find anything big enough to see in this filter. I am hapy with this arrangement and think it will work out good. Not flying yet though so all things are subject to change.

Bevan