Craig B.

Curious to see how guys mount their filters and whether the mounting position has caused any problems? Thanks for your replies.

Craig

Ehab

My Feedback: (44)

If I am using a UAT(which is now 100% of the time), I do not use any filters. But I do triple filter the fuel going in....

rhklenke

My Feedback: (24)

You need to mount the JetCat filters vertically if you possibly can. If you don't, the filter is so fine, it filters out the "micro bubbles" of air and they accumulate under the edge in the filter. Then when the bubble gets big enough, it "burps" out a big one with predictable results - been there, seen it...

Bob

acw

My Feedback: (1)

I mount my filters vertically if possible. If not, I run the fuel pump manually and tap the filter while moving the fuselage nose up. I'm always surprised by the amount of air that get trapped in there.

I believe that when the filter is horizontal, some air accumulates on top of the filter. One up leg like a take off will then potentially release the air.

Arnaud

fasteddi

hi arnaud
that is exactly what happens to me with my yak54 turboprop- take of,f than nose up and the turbine shut off.....................finished!!!
since that- filter in vertical, i never have a problem like that again!!!

uwe

rcguy!

My Feedback: (69)

I mount them as JetCat suggests. Who would know better then the manufacturer?

Dave

Kevin Greene

My Feedback: (85)

Big NO NO, Ehab!!! What filters your fuel after it leaves the pump???....Fuel pumps shed metallic particles as they run/wear...All of this goes directly into the turbine to clog up fuel sticks, destroy bearings, causes the fuel solenoid to stick, etc...

Always use a JetCat style filter after the pump but before the fuel solenoid....

Kevin

mr_matt

My Feedback: (10)

In addition to mounting vertically, I recommend that you do not hard mount them. If they are free to move a bit, the natural vibration tends to clear any tiny bubbles out of the filter.

Ehab

My Feedback: (44)

Most turbine mfgs say that about the pump. But also most if not all turbines have a final filter inside the front cowling. I have yet to hear about a turbine that had all or some of its injectors clogged because of pump minute particals. Again, I am talking about isolating and proving a problem exist because of ONLY a pump shedding particles not other causes such as bad fuel, oil, fod etc etc.... May be some turbine mfgs on this forum would like to chime in their findings.

BTW, I used the Festo 4mm clear platic filter in the past and never had a bubble out of it....

highhorse

My Feedback: (2)

EDIT: Doh, nevermind. Didn't read carefully enuff and basically duplicated Kevin's post.

Deleted mine.

Sorry Kev.

junglejet

Filter before the fuel goes in the tank/s and a filter in the UAT, how much more do you need????

Kevin Greene

My Feedback: (85)

Ehab....The final filter in the turbine, from my understanding, is not as fine as the JetCat inline filter...The final filter is a last chance trap that should not be relied upon as part of the primary filtration system...Remember, a percentage of your fuel is sent to the bearings to lubricate them....Bottom line is that the pump does wear and put out fine particles....Why take the chance???

Kevin

Ehab

My Feedback: (44)

I used to filter a lot in the past, then I personally witnessed many flame outs and crashes due to filters (either mechanicl problems or user errors) that I decided to change my install. My highest flights were on a Bobcat w/o filter and no problems. I stopped counting after 350 flights. Sold the P120 and last I heard was still running fine (about a year ago)....

Pricipally, a filter used properly does no harm, but I ask if there is any reported case of failure due to no filter in line and pump particles...I like to know the facts Kevin, as I respect your opinoin...[8D]

Kevin Greene

My Feedback: (85)

Hey...No problemo Ehab!!!...Too bad you now live half way around the world as we could be discussing this over a pizza and a pitcher of beer while watching college football on the big screen...[8D]...I didn't mean any harm....And I, too, respect your opinion...[sm=thumbs_up.gif]...

We all have our ways of doing things and like you I have had success with my turbine engines...I can boast of NEVER having one flameout in all of the years I have been flying turbines...I'm very particular...No, I'm down right anal when it comes to plumbing a turbine...

Now I've gone and done it...My entire fleet will now be probably destroyed by flame outs on take off...[:@]...Is there any wood close by to knock on???

Kevin

Ehab

My Feedback: (44)

Yes there is...your head...could not resist, you left it wide open buddy

Crazy4Flight

My Feedback: (540)

I have seen 3 flame outs due to trapped air in filters, therefor I do not use filters on board. I filter fuel after the fill pump. A new jet will get the fuel system filled an flushed several times before flight.

But I do have a filter on my tank vent!

Why?? To keep crud from entering the clean fuel system.

Didier

I completely agree with EHAB. Fuel filters is the number 1 cause of flame outs and eventually causes your jet to crash... (if murphy's law is applicable).
No way there is going 1 fuel filter inside my jet!!!! I use the best fuel and filter it before it go's in to my jet.
I have a couple of friends that still runs jetcat's with serial numbers somewhere between 100 and 150 that never had any flame outs after removing the filter.
Jetcat seems never to have reported about dirty fuel sticks.

Craig B.

I understand all of the opinions above but I wonder about the plausibility of a large single air bubble passing through the membrane of the filter and entering the out-line in the form of a single uninterrupted air bubble. I agree with the "why take the risk" idea as well, just trying to understand how 6-7 jets have flown hundreds of flights like this without a single flameout?....touch wood!

Craig.

Ehab

My Feedback: (44)

To date, I have not known of, or heard of, nor told that there is a single problem related to "no filter in line". I have seen, heard and was told of many flame outs due to air bubbles in the line, for various reasons. As a result, I concluded that an extra filter in line will add to a failure rate rather than prevent dirt from going in. Again, assuming proper fueling practices...

rhklenke

My Feedback: (24)

On the other hand, after I started mounting the fuel filter vertical as JetCat suggests, I have not had a single flame out due to bubbles in the line in many, many hundreds of flights...

Bob

Craig B.

Hi guys,

Interesting finding......all of the manuals, old and new, that I have (which have come from Jetcat Germany) have no mention of mounting the filters vertically but Jetcat USA's manual does. Obviously an addition to the manual made by Jetcat USA.

Craig.

Kevin Greene

My Feedback: (85)

Nah....If you knew me better you would say my head is harder than that......At least that is what my wife says...[:@]...

This is how I have my filters mounted...No flameouts so far...

Now to ask...Do I have my filter pointing in the correct position or is it backwards???...I talked to Bob Wilcox and he said that it doesn't matter but others here on RCU say that there is a definate orientation....

Also, some say to make a loop with the fuel line before having the filter mounted vertically...My way, the bubble, if there is one, stays at the top of the filter...When running the turbine for the first time I shake the UAT as well as thump the fuel filter to get out all of the bubbles...

Another thing is that I never de-fuel the plane completely...I always leave the UAT full of fuel and all of the components upstream have fuel in them, up to the fuel solenoid....If you empty the UAT you will have to go through the bubble purge process all over again every time you fly...My UAT's have never had black algae found in them...Even if they did all you have to do is to order a new internal UAT sock from Todd at Dreamworks..

Kevin

Vincent

My Feedback: (61)

Kevin,
You have the filter installed correctly... I usually run the 6mm tubing from the uat right up to the pump inlet, then 4mm downstream.With a uat onboard and good filtering between the fuel can and the jet i don`t even install the filters anymore. I had a filter air bubble in my BVM sabre last year cost me lots of repairs. When i got the Sabre flying again i eliminated the filter.
V..

reo

My Feedback: (130)

I gave up on JetCat filters years ago. Love their engines but the filters are more trouble than they are worth. I use 6 MM Festo filters after the pump with absolutely no issues whatsoever. I do make every effort to mount them vertically and not fastened down to anything in the airframe.

Craig B.

Hi guys,

Well tonight I ran some interesting tests with a mate of mine who is a mechanical engineer specializing in hydraulics. Both of us have been very skeptical about the ability of the filter to cause problems by the venting of large air bubbles in horizontally mounted filters.

We set up a test rig with a jetcat fuel pump and filter rigged as you would in the aircraft. The fuel pump was rigged to a regulated power supply. Pump start voltage was 0 volts in all tests. In all tests the filter was emptied of all fuel prior to the commencement of each test. For each test, the filter was positioned in the test position (horizontal or vertical depending on the test) and the pump voltage (Pv) was increased to 0.7 volts which I think is pretty close to the idle voltage of most of the engines. The timing for the rate of increase of Pv was similar to that for normal engine startup time. Pv was subsequently varied according to the tests below....

TEST 1- filter horizontal, startup to 0.7 volts (alot of air expelled from fuel lines and filter...we have all seen this on startup). Pv increased gradually...small air bubbles expelled intermittently from filter (note, no air in fuel lines leading to pump by this stage) up to Pv of 1.4-1.5 volts. At greater than 1.5 volts it was not possible to get more visible air bubbles out of the filter even when it was changed from horizontal to vertical. I think that, and I may be corrected on this that max full throttle pump voltage is around 2.2 volts.

TEST 2- startup sequence the same with filter vertical. Note that as the Pv was increased, the pattern of bubble passage from the filter was the same or more prolonged with the filter mounted vertically. ie. the filter position seemed to make no noticeable difference to the passage of air, if anything, the problem seemed worse with the filter vertical. By this I mean, that the air did not vent more easily from the vertically mounted filter. If anything, the air seemed to take longer to vent from the vertically mounted filter with respect to the horizontally mounted scenario, but the difference was not huge.

TEST 3 and 4- as for tests 1 and 2 but filter orientation was changed repeatedly to resemble change in aircraft attitude. Note that changing filter orientation only affected air venting tendency if pump voltage was kept to below 1.4 volts at all times prior to changing the filter orientation. ie. at low flow rates, and only if pump had not been ramped up to above 1.4 volts, changing filter orientation could vent air more easily. If high flow rate applied at any time during test, prior to changing filter orientation, then changing orientation had no effect, probably because all air had vented by this point.

TEST 5- Effects of vibration....Tests above were repeated while subjecting the filter to vibration (as if it were hard mounted) and and also shaking the filter as might occur if it was not hard mounted. Both could elicit bubbles from the filter but the size of the bubbles was bigger if the filter was not hard mounted. At no stage in any test was it possible to create a bubble that was any longer than a few mm in the fuel line. It would appear that it was not possible to produce a bubble or even stream of bubbles that would have the remotest chance of shutting down an engine.

Conclusion....if you are in the habit of taking off at 1/4 to 1/2 throttle, then your filter orientation will be critical. If you run your engine up to full power prior to leaving the ground, filter position seems to make no difference at all.


COMMENTS- People often make the mistake of taking a static view of a bubble in the filter. The fact is that the flow rate and size of the filter chamber are highly relevant as is the pore size in the filter element and the viscosity of the liquid. The flow rate through the filters is so high that the bubble does not remain at the top of the filter but it is displaced around the periphery of the filter membrane housing. Due to the pressure generated by the pump, the vast majority of the air is broken up as it is forced though the membrane of the filter. The point is that the pressure within the filter and the turbulence generated buy the fluid movement are the most influential forces acting on the air bubble, not the buoyancy of the bubble. This is why the venting process is most affected by the pump voltage, more so than any other variable like filter orientation.

From our tests, there was no evidence to support the conclusion that you should mount you filter vertically or that you should avoid hard mounting your filter, almost the opposite in both cases. As for those who will claim that they have seen an air bubble come from a filter and shut an engine down....well, with respect, you did not see that did you, you can only have assumed that is what happened and there is a big difference there. The above test results really call those assumptions into question.

Having seen the results of the tests and never experienced an engine shut down in flight (touch wood), I am not going to do anything other than run my engine up to full power for a couple of seconds if I have serviced my filter, fully emptied my aircraft or fuel lines or if I am flying a jet for the first time. I do this as a matter of routine anyway to make sure the engine parameters seem normal and to ensure that I have no vapor being generated due to obstructions in the fuel system.

My mechanical engineer mate is in the process of running some simulations on the filter to see what the computer says. I will report back when the results are to hand.

Hope this is of interest.

Craig.