Fuel system non return valve
 

Does anyone know the opening pressure of the non return valve(Reversion valve). Yes I'm building my own quick disconnect fittings for my carbon fibre tank. I just need to know the non return valves spring rating.

not sure - but I guess it'll just need to be a weak spring behind the ball bearing as the weight of the fuel will help keep it closed anyway. If your making your own set do you intend to knock a few up and offer them up for sale on the site ?? ps let me know if you do and for how much.
cheers

Neil

Why do you need a non return valve? The fuel just goes round and round driven by the pump against the pressure regulator.

Douglas

Ahh, but when you discoinnect the Q/Ds the fuel ****es out on the floor.

Douglas, the Carbon tank needs 2 disconnects 1 each side of the tank, at it's lowest point, so it's a little different to the alloy / steel standard tanks.
In my alloy tank the return side is quite high up in the tank so no opportunity really for all of the fuel to **** all over yer boots...

Neil

Neil, are you able to provide a sketch or pics, because I'm not convinced about your explanations ...
There's no rigid fuel tubes into a carbon tank, compare to steel (no idea about alloy ...)

My couple of Carbon tanks 93 and 94 have got original reversion valve on the return way ...

On all the self sealing fuel connectors I have seen the action of inserting the male portion pushes open a spring loaded plunger valve. A bit like the garden hose connectors. The connector is then open both ways for the fuel. The rating of the spring has no effect on the fuel flow.

Douglas

The purpose of the non return valve in the return line is to ensure that when the pump runs dry, the fuel circuit still contains fuel. No other reason. ( Obvious solution, never let it run dry). But if the Ducati boys have one then you need one, after all they are the wizards.

If you look at the drawings, the fuel tank connections can in theroy be anywhere. The pickup for the pump is at the base of the pump at the low point. the return outlet is also there, but it has been up to the top of the tank and through the "Degasser", then the hose goes back down again.

Douglas. The disconnect fitting is not a non return valve. and your right the sping has nothing to do with anything other than closing the line via the valves in them.

Rob. I'm going to use an inline male plastic quick disconnect inserted into a 20mm adaptor on both conectors. One will have a non return valve. They will be made of al alloy. This will stop the issue of fuel ****ing out the pressure line from the tank when you disconnect it. Have to wait a week or so to see the results.

Griff

All, I thought that the LHS connector was a non-return valve - it's actually called a 'fuel reversion valve' in the parts book, whereas the other side is just called a 'union', this led me to think it was a non-return type.
I've bought some quick disconnect connectors which are brass and chrome plated from a guy in the states - they have a 90 deg kick in them but they look great and are leak proof on male and female end. They are not directional.
The thread size is not right but a mate of mine is knocking up an adapter to screw into the tank 1st.
I'll post some pics on completion.
cheers

Neil

http://cgi.ebay.com/ebaymotors/Quick...mZ46 16900337

check out his disconnectors.

Neil

jgriff, I don't understand your explanation / reasoning.

The return side is only dealing with unused fuel from the injectors, these are pumping fuel back under pressure and this is fed thru the pipework and connectors into the degasser, and then straight back into the tank & not to the pump.

It's doing this as there are only certain throttle openings and revs where just about all of the fuel supplied is used by the injectors, at points below this only one injector is firing but the system is seeing fuel at the same pressure as when at high revs, hence the return of fuel under pressure.
On single injector motors the same symptom occurs thru the rev range, check out the injection timing charts in the falloon books, or the moto one performance index.

I know that the degasser was fitted as Duc had big problems with tank pressurisation which starved the motor of fuel, even when a tank breather was fitted - I think it starved the motor of fuel as the back pressure was greater than the pump pressure - hence the degasser and also the 'non-reversion valve', the valve halted back pressure and allowed one way flow only and a motor not starved of fuel.

This is the only logical reason I can come up with for it being there on the works bikes, more fuel demand, bigger pressures, bigger heat soak etc...led to tank over pressure
cheers

Neil

Yeah strange isn't, whats worse is I can't find where i read it again. I always just thought it was to stop the fuel coming out when you disconnected the tank, as per the manual.
Ok the fuel system. The pump puts out somewhere between 3-5 bar constantly. it draws from the bottom of the tank. Fuel leaves the tank and feeds the injectors. Next in the circuit is the pressure regulator, the pressure regulator bleeds off any pressure in excess of 3 bar to the return line. (Aftermarket can be set to 4.5. This gives more fuel per injector cycle, and hence more go. FIM). 3 bar is 44 ish psi. So the the return pressure can be any where from 0 to 2 bar depending on injector demand. Max pump pressure 5 bar minus system pressure 3 bar.
The degaser just removes any air that may be in the circuit, from cavitation or maintence.(In avaiation we use to call them swirl cans.)
The tank needs a breather to allow for over and under presurisation. Use the fuel you get negative pressure and pump will starve for fuel, and cavitate. Add heat and tank will have positive pressure. Tank will get fat and burst. A little positive pressure means the pump doesn't have to work so hard. So you would think that this is a good thing. But it will cause more pressure on the back surface of the pressure regulator diaphram, thereby effectively increasing the regulators spring force and raising regualted pressure above 3 bar.
So our non return valve now has two jobs. Stop fuel ****ing out all over the place when you take the tank off. (Fuel pump has its own non return valve), and stops an increase in fuel pressure regulation in the event of a fuel tank increase in pressure, by maintaining a set return line pressure using the opening spring force in the Non return valve.
How about that then? Sound better.

[Edited on 4-3-2006 by jgriff]

[Edited on 4-3-2006 by jgriff]