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Silver hawk Fuel Injection Question

Robb

Well Known Member
I am in the process of doing my first annual inspection on my RV7. I am removing all the panels and so far I have not see any type of fuel filter in the system. I do have the electric fuel pump between the seats on the lower console. I checked all the previous logs and do not see any mention of it. I am used to a gascolator in my Husky. If not it sure looks like it should have some type other than the one inside the fuel injection system.
 
I am in the process of doing my first annual inspection on my RV7. I am removing all the panels and so far I have not see any type of fuel filter in the system. I do have the electric fuel pump between the seats on the lower console. I checked all the previous logs and do not see any mention of it. I am used to a gascolator in my Husky. If not it sure looks like it should have some type other than the one inside the fuel injection system.

There is a fine screen filter in the AFP pump system (between the seats). Its the big gold anodized cylinder. Contact Airflow Performance in Spartanburg, SC for details if you do not have original documentation.

There is also a VERY VERY fine screen filter in the SilverHawk fuel injector servo body. Contact Precision Airmotive for documentation regarding maintenance.

Both of these filters should be inspected and cleaned at the annual condition inspection.
 
Fuel fliters

In Canada our regulators make us also install a gascolator. My annual, the afp filter comes out in tunnel between knees, as well as all fuel connections there checked. Also, the fuel servo is inspected for and the screen pulled on that and the gasket/ring replaced. My andair gascolator pulled and cleaned/inspected.

If you bought the plane, I would contact the previous owner/builder. Pretty important stuff. He can surely tell you what there is,where it is, and what they did as normal annual routine. Not something to skip or not fully understand.
 
With the EX-5, Precision requires a 35 micron filter installed downstream of all pumps and valves except the engine driven pump.

In contrast, the cylindrical AFP filter supplied with their boost pumps is 125 micron, and is installed upstream of the electric boost pump. As such, a builder may have deleted it.
 
I have this on my list of things to figure out. Dan are you saying that the 125 filter is ok or should a 35 be installed IAW the Precision recommendation? I installed the Vans supplied filter/pump and FWF kit on my IO-360-M1B.
 
I have this on my list of things to figure out. Dan are you saying that the 125 filter is ok or should a 35 be installed IAW the Precision recommendation? I installed the Vans supplied filter/pump and FWF kit on my IO-360-M1B.

I don't think a 125 micron filter prior to the electric boost pump can be a bad thing, regardless of Precision's instructions. Besides, I'll bet Don at Airflow wants that 125 micron filter in front of his boost pump, just to protect the pump.

I would not put a 35 micron screen in that AFP canister without careful fuel flow checks with the engine compartment hot, hot, hot.
 
With the EX-5, Precision requires a 35 micron filter installed downstream of all pumps and valves except the engine driven pump.

In contrast, the cylindrical AFP filter supplied with their boost pumps is 125 micron, and is installed upstream of the electric boost pump. As such, a builder may have deleted it.

Now that's got me curious. Specifically about the mesh of the finger screen installed in the EX-5 servo. I see the note about 32 micron filtered fuel supply by Precision but I have not found reference to what the internal screen is. Just by observation, I have a hard time believing it is finer than 32. I guess if it is, I will have learned something.

No intent to change anything since my system has had very little debris on the last 4 annuals (480 TT). Hardly worth the disassembly (but yes I will continue to do it). :)
 
I was not actually thinking about changing out the 125 micron filter before the pump. The question was about the wisdom of adding a 35 micron filter somewhere after the boost pump?
 
I don't think a 125 micron filter prior to the electric boost pump can be a bad thing, regardless of Precision's instructions. Besides, I'll bet Don at Airflow wants that 125 micron filter in front of his boost pump, just to protect the pump.

I would not put a 35 micron screen in that AFP canister without careful fuel flow checks with the engine compartment hot, hot, hot.

I note that the Andair pump that I and many others have has their filter before the pump. So the pump manufacturer wants it *before* the pump, the FI manufacturer wants it *after* the pump, and none of them, as far as I can tell, are small enough. :)

I don't know what the upshot of all this is...I'm not changing my system, as it's worked flawlessly for nearly 400 hours now and I've not found anything in any filter since the first 25 hours (just a hint of some blue paper fibers from initial assembly). YMMV.
 
There is a fine screen filter in the AFP pump system (between the seats). Its the big gold anodized cylinder. Contact Airflow Performance in Spartanburg, SC for details if you do not have original documentation.

There is also a VERY VERY fine screen filter in the SilverHawk fuel injector servo body. Contact Precision Airmotive for documentation regarding maintenance.

Both of these filters should be inspected and cleaned at the annual condition inspection.

Bill, you made me curious and I referenced the Precision Airmotive EX-5 servo manual. It reads " The airplane's fuel filter needs to be maintained to ensure that the servo gets clean fuel. The fuel filter inside the servo is a last chance filter. This filter does not need to be checked or cleaned unless it is suspected that contaminates have entered the fuel line after the aircraft's fuel filter."

Hopefully, I saved you some headaches at annual :)
 
Bill, you made me curious and I referenced the Precision Airmotive EX-5 servo manual. It reads " The airplane's fuel filter needs to be maintained to ensure that the servo gets clean fuel. The fuel filter inside the servo is a last chance filter. This filter does not need to be checked or cleaned unless it is suspected that contaminates have entered the fuel line after the aircraft's fuel filter."

Hopefully, I saved you some headaches at annual :)

Hmmm. Now things start to make sense. If one externally filters to the same particle size as the internal screen (the 32/35 mesh requirements noted earlier in thread) then the internal screen will never catch any debris. No need to check it.

In the vans std setup, the AFP is a coarse screen so the EX5 screen may pick up debris. I'll keep cleaning it for that reason. Thanks for the info! :)
 
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I see the note about 32 micron filtered fuel supply by Precision but I have not found reference to what the internal screen is. Just by observation, I have a hard time believing it is finer than 32.
I have an Andair 62 micron filter upstream of my Andair boost pump. Based on information I'd previously received from Mattituck, I hadn't planned on installing another filter after the boost pump but I decided to email Precision and confirm what I'd heard earlier from Mahlon. Their words were that anything finer than the 70 micron screen in the servo would be acceptable.
 
Thanks for the info. I did find the filter it is down in the enclosure between the seats and it is a large red cylinder type that is cleanable. It appears top be a bitch to get at. Funny thing is I see no mention of any maintenance in the log books anywhere. I have 230 hrs TT so I doubt its bad but we will see.
 
Hmmm. Now things start to make sense. If one externally filters to the same particle size as the internal screen (the 32/35 mesh requirements noted earlier in thread) then the internal screen will never catch any debris. No need to check it.

In the vans std setup, the AFP is a coarse screen so the EX5 screen may pick up debris. I'll keep cleaning it for that reason. Thanks for the info! :)

Wait wait. This is not true. The servo screen is the screen of last resort. Debris can come from a number of places including hoses, pumps, diaphrams, etc. Check it per manufacturers specs and dont neglect it due to other filters up stream regardless of micron.
 
Wait wait. This is not true. The servo screen is the screen of last resort. Debris can come from a number of places including hoses, pumps, diaphrams, etc. Check it per manufacturers specs and dont neglect it due to other filters up stream regardless of micron.

Right..and the manufacturer's instructions say:

This filter does not need to be checked or cleaned unless it is suspected that contaminants have entered the fuel line after the aircraft's fuel filter."
 
Right..and the manufacturer's instructions say:

I had an occasion to call them recently and asked as this had just come up. Despite what the instructions say, they do recommend you check it occasionally. It is super easy to do. I do mine at each CI.

PS - I have never found anything in it. Nothing, zilch, nada. I only occasionally find stuff in the upstream filter. A microscopic piece of fuzz, a pin head spec of something black, although just yesterday doing my CI, I found a very small goldish metallic spec, like super tiny can hardly see with the naked eye. I think it might have been from the fuel tank drain as I removed them to drain that tanks, or it could have been from the selector valve as I removed it for replacement. Who knows.
Anyway, nothing exciting....
 
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I had an occasion to call them recently and asked as this had just come up. Despite what the instructions say, they do recommend you check it occasionally. It is super easy to do. I do mine at each CI.

I'll go by what they've *written*. Anybody can say anything over the phone.

Plus...the more stuff you needlessly take apart, the more chances you get to mess something up, and the last thing I want to mess up is my *fuel system*. Remember the Waddington effect?

Manual says don't take it apart unless you (have or) suspect contamination upstream. Sounds like good advice to me.
 
Wait wait. This is not true. The servo screen is the screen of last resort. Debris can come from a number of places including hoses, pumps, diaphrams, etc. Check it per manufacturers specs and dont neglect it due to other filters up stream regardless of micron.

Hi Mike,
I may have mislead you with the way I wrote my post. I meant to imply that I would keep cleaning the servo filter.
 
I'll go by what they've *written*. Anybody can say anything over the phone.

Plus...the more stuff you needlessly take apart, the more chances you get to mess something up, and the last thing I want to mess up is my *fuel system*. Remember the Waddington effect?

Manual says don't take it apart unless you (have or) suspect contamination upstream. Sounds like good advice to me.

Peter is who I spoke with. He has been there in the tech support role for quite a long time and knows the product very well.
However, I get what you are saying and the choice is certainly yours to make. I don't think inspecting this part is needless, but we can agree to disagree.
I would say that I am probably your best advocate. I have never found anything in that screen, ever.... but I will still keep looking.
 
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This is from my Precision manual:

Fuel%20Servo%20Maintainance_zpsgbggtgpg.jpg


Calls for 50 hour inspection of the inlet strainer or per the airframe manufacturer.

So as the builder, I inspect mine at the annual CI.

I also check the boost pump filter annually.
 
This is from my Precision manual:

Fuel%20Servo%20Maintainance_zpsgbggtgpg.jpg


Calls for 50 hour inspection of the inlet strainer or per the airframe manufacturer.

So as the builder, I inspect mine at the annual CI.

I also check the boost pump filter annually.

These where what I had as well. However, I think there is a newer instruction set out there that might be causing the confusion. I was "told", don't want to start any rumors, that the manufacturer found people where damaging the inlet and it just wasn't worth the trade off. If that is true, some people just shouldn't do their own maintenance.
Please, this is hear say....so treat it as such.
 
The one I posted is dated Nov 8, 1996 and not for the experimental model.
Maybe there are different requirements for the certificated version, or as you said, maybe just updated their documents.
 
Fuel servo filter inspection

I found this thread in the archives and I'm resurrecting it. I notice in this thread that several posters have stated that they clean their Precision Silver Hawk fuel servo filters at annuals but none of them have ever found any debris in the filter.

I'm a bit suspicious of this particularly when the majority of builders have the stock standard Van's AirFlow Performance auxiliary pump/filter upstream which is quite coarse at 125 micron. The SilverHawk servo filter on the other hand is considerably finer at approx 70 micron.

My question is: How do you know that you have no debris in the servo filter when it seems virtually impossible to visually inspect the interior due to the extremely narrow dimension of the filter.

And what technique is being adopted to "clean" the servo filter. I don't believe Precision has any specific cleaning technique in their installation manual.
 
Good question. I clean with MEK, tap out on end, straining through a paper filter element, then repeat, carefully, with compressed air also through the paper filter. I inspect the paper filter with a 10x magnifier.
Whether or not that process dislodges any particulates, or whether or not I can see them in the paper filter is certainly questionable.
I changed my inspection interval and no longer check at every CI. There is a lot of filter area in that finger screen and the odds of not seeing anything in the 125 micron filter and having it pass enough smaller contaminate to clog the 70 micron filter I would think are pretty slim.
Right, wrong, or indifferent, that is what I do.
 
Right..and the manufacturer's instructions say:

This filter does not need to be checked or cleaned unless it is suspected that contaminants have entered the fuel line after the aircraft's fuel filter."

But that is assuming you follow ALL of their instructions, which include a filter DOWNSTREAM of all pumps, which most RV's don't follow. They put the filter upstream of the pump. This means that any debris shed from a deteriorating pump will end up in their screen, which is not sized to handle much debris.

Larry
 
But that is assuming you follow ALL of their instructions, which include a filter DOWNSTREAM of all pumps, which most RV's don't follow. They put the filter upstream of the pump. This means that any debris shed from a deteriorating pump will end up in their screen, which is not sized to handle much debris.

Larry

Spot on Larry. And Precision's installation manual also calls for a 30 micron filter upstream of the servo. The Airflow Performance boost pump/filter that virtually every RV with fuel injection currently has (as specified and supplied by Vans) has a quite coarse 125 micron filter. And generally there is no gascolator specified by Vans on the fuel injected models. Gascolator filters are typically around 30 micron.

The end result is that most fuel injected RVs have a relatively coarse 125 micron filter upstream of the boost pump and the only other filter is the Precision servo filter which is approx 70 microns. In other words coarse debris will lodge in the AirFlow filter and finer debris will pass through and lodge in the Precision servo filter.

In other words the statement that "the Precision servo filter is only a last chance filter that does not need to be regularly inspected" is simply not true for the fuel system set-up that most RV builders have in their fuel injected Lycomings.

As I've said previously, most builders report that they never find debris in their servo filter (so they tend to stop inspecting it). But that is because a visual inspection of the servo filter is realistically impossible due to the very narrow internal dimension and the fact that the internal bore is the upstream side of the filter. They probably have debris in that filter but they cannot see it.

I flush both my AirFlow boost pump filter and my Precision servo filter with mineral spirits and then drain the fluid through a white paper filter. Then I inspect the paper filter under my microscope. Typically I find microscopic debris that is generally not visible to the naked eye in both the AirFlow and Precision filters. As would be expected the debris in the 125 micron filter is coarser and the debris in the 70 micron filter is finer.

I highly recommend that all builders with the typical Vans fuel injected fuel system and no gascolator thoroughly clean their servo filter at every annual. Just taking it out and looking at it cannot determine if it is actually clean. Actually the same can be said for the AirFlow filter...don't rely on a visual inspection...take it out and clean it even if it visually looks clean.
 
Can anybody post a source for a 30 micron cleanable/inspectable filter and suggest a suitable mounting location/method in a FWF (hot) environment?

Bevan
 
Well stated Bob and Larry. Your timing is good as I haven't missed any inspection intervals. I will continue as I have before with the inspection and cleaning regime.
I have not heard of a fuel starvation incident. Don't want to be the first.
 
The end result is that most fuel injected RVs have a relatively coarse 125 micron filter upstream of the boost pump and the only other filter is the Precision servo filter which is approx 70 microns. In other words coarse debris will lodge in the AirFlow filter and finer debris will pass through and lodge in the Precision servo filter.

Andair fuel filter is 62 microns.
 
Can anybody post a source for a 30 micron cleanable/inspectable filter and suggest a suitable mounting location/method in a FWF (hot) environment?

Bevan

Bevan, you should have a Gascolator (Canada eh?) after your boost pump, this should catch & illustrate any debris before it becomes an issue down stream. Is it a good idea to string a series of filters to protect a filter?
 
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