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Old May 24, 2015, 06:33 PM
LIFrancis is offline
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Question
Pluming my fuel system

Is there a basic diagram of how to plum the fuel system with a main and UAT? It's on a Heli with a Wren44. Just for some reassurance...
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Old May 26, 2015, 02:39 PM
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From BVM, although Wren says the valve should be on the pressure side of the pump, NOT the suction side
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Last edited by Mav62; May 26, 2015 at 02:47 PM.
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Old Jun 03, 2015, 05:29 PM
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I'm surprised BVM would put this out: key error here is placement of the shutoff valve before the pump. This should always be AFTER the pump and closest to the engine.

Otherwise, looks normal. Some prefer running separate lines to the header tank, but you can do it either way. Either way, for saddle tanks, it is key to ensure your tube lengths and setups are absolutely identical all the way to the clunks. Otherwise, the tanks will drain at different rates. Bear in mind, on a parallel saddle tank setup, if they are draining unevenly, once the vacuum breaks in one, it is done supplying fuel, even if it is not empty. Think about that in terms of where the tank is and what the aircraft is doing in flight (rolls, loops, inverted flight etc.). For this reason, some prefer to plumb the saddles sequentially.

Also, on parallel saddles, ensure you are teeing the vents as in the diagram. Do not vent separately.

Don't know what size you are engine you are running, but I would not use the BVM UAT on anything > 120 size, as they tend to collapse a bit under suction, which significantly reduces the working surface area of the trap. GBR makes some nice rigid UATs which work better with the bigger setups and suction levels.

EDIT ; didn't see Wren 44. BVM UAT will do fine for that.
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Old Jun 05, 2015, 11:34 AM
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I was told to put the shut off valve on the suction side of the pump. Why would you want it on the pressure side?
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Old Jun 13, 2015, 08:54 PM
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Quote:
Originally Posted by why_fly_high View Post
I was told to put the shut off valve on the suction side of the pump. Why would you want it on the pressure side?
With the shut off valve close to the engine on the pressure side, in case of emergency you will be able to shut off fuel to the engine immediately. All turbine installation diagrams from all manufacturers show the shut off valve on the pressure side, so I also assume they know what they are doing.
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Old Jun 14, 2015, 11:17 AM
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Quote:
Originally Posted by why_fly_high View Post
I was told to put the shut off valve on the suction side of the pump. Why would you want it on the pressure side?
To add to the previous comment... The valve is also on the pressure side, close to the engine to prevent fuel from trickling into the turbine and possibly causing a Hot Start on your next fire up.
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Old Nov 23, 2015, 02:22 PM
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Quote:
Originally Posted by Dionysus View Post
With the shut off valve close to the engine on the pressure side, in case of emergency you will be able to shut off fuel to the engine immediately. All turbine installation diagrams from all manufacturers show the shut off valve on the pressure side, so I also assume they know what they are doing.
I have my festo shutoff valve on the inlet (tank side) of my pump on my JM vt80 and if I shut off the fuel valve before the engine shutdown switch , the turbine stops immediately .... No burps , nothing. If the valve is there , like where is the pump going to get fuel from ? On restart after fuel up and next flight there is no smoke or flame out the exhaust so for me it works just fine thus way.

If you are getting fuel into the turbine after fuel shutoff ,then you have issues with your turbine solenoid valves.
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Old Nov 23, 2015, 07:49 PM
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You are running Festo fittings on the suction side of the pump?!! That is just begging for a flame-out.
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Old Nov 23, 2015, 09:02 PM
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Just the fuel shutoff valve . Had my install checked out by local jet guy we nickname Dr. turbine I think it us as he has been into turbines since they first came over from Europe and he saw no issues.
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Old Nov 23, 2015, 09:39 PM
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Festo fittings are designed ONLY for pressure, not vacuum. Festo themselves clearly indicate they are not suitable in the product literature. You will pull air in at some point.

I have seen lots of veteran jet guys (and warbird guys) do stupid stuff on installs. Just because he has done it this way for a long time, does not make it right.

Please correct this. Not worth losing your model. And, you will also be placing the shutoff valve on the pressure side of the pump, where it belongs. That's why your shutoff valve is a Festo.

Also, the jetsmunt manual is notorious for showing and incorrect filter setup and not showing any fuel system diagram at all. One of the purposes of the fuel filter on a turbine is to catch any metal particles that might be emitted by the fuel pump, which could cause the solenoid to jam open, or could clog the micro fuel ports. So it too goes after the pump, not before. The Jetcentral, Jetcat and Kintech manuals show a correct fuel system installation. UAT, Tygon or Poly large-bore to pump, then the filter, then shutoff, then solenoid or motor Festo connection. Everything after the pump is Festo, 3 or 4mm. Also, using small Festo on the suction side of the pump (where it is weak) degrades pump performance and overworks it.

Basic rule of thumb on a turbine fuel system: never use Festo on the vacuum side of the pump and never use Tygon on the pressure side.
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Old Nov 24, 2015, 02:52 AM
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Quote:
Originally Posted by TTRotary View Post
Festo fittings are designed ONLY for pressure, not vacuum. Festo themselves clearly indicate they are not suitable in the product literature.
Perhaps you should read festo's literature. The ball valves are rated to minus 1 bar, i.e. minus 15psi. It's a very common myth that Festo are pressure fittings only but a simple read of festo's own specifications soon dispels the myth. The reason why so many Festo filters misused as fuel filters soon develop bad leaks is because they are designed for suction not pressure!
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Old Nov 24, 2015, 06:05 AM
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Perhaps you should read festo's literature. The reason why so many Festo filters misused as fuel filters soon develop bad leaks is because they are designed for suction not pressure!
With all due respect, this is ridiculous. Festo's own product literature on the.de site is clear in this respect. Please do not post nonsense like this. What purpose does it serve?

Apart from this, just look at the schematic for a Festo fitting. It is obvious that it uses pressure to augment the grip and sealing of the fitting. More pressure, more sealing power.

Besides which, the suction side of a jet pump delivering 3-5 bar to the turbine is going to be a lot more than 1 bar. Use your head, man.

But hey - it's your money and your grief. Run Festo fittings wherever you want, but don't come complaining on here if you lose your plane due to air in the system .

I'm out.
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Old Nov 30, 2015, 08:50 PM
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TTRotary is correct.

Please look at the turbine manufacturers schematics for the fuel plumbing. I have a Jetcat and a Jet Central in front of me and the shut-off valve is on the pressure side.

Two BIG reasons.

1) As TTRotary states, the pressure helps seal the connection. Yes, they will work under slight vacuum, but that is not how they are designed.

2) You NEVER close off the suction side of a pump.........a pump will destroy itself with cavitation, but will only build pressure if the outlet is blocked.

I only have 36+ years of rebuilding pumps.......what do I know?

But......to each his own. We are only trying to help with advice.
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Old Dec 01, 2015, 05:29 AM
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Quote:
Originally Posted by TTRotary View Post
With all due respect, this is ridiculous. Festo's own product literature on the.de site is clear in this respect.
Then produce it.
Here is festo's data sheet for the ball valves showing rating to minus 1 bar https://www.festo.com/cat/en-gb_gb/d...N/HE_VB_EN.PDF

And as per an article in a recent issue of the RC Jet International magazine, the clear body Festo filters that are being used as fuel filters on the pressure side are actually air suction filters, not intended for either fuel or pressure hence the high failure rate, see https://www.festo.com/net/SupportPor...LTERS_ENUS.pdf
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