Return Flow function

[G3WGV]

I've now bought a D120 and have been spending some time tinkering with the configuration. It has version 5.1.1 firmware, configured for the Roatx engine. One thing that caught my eye is the RETRN FLOW parameter in the Fuel flow section. The manual, somewhat enigmatically, states This function is generally used only by Original Equipment Manufacturers (OEMs).

I assume this parameter is to permit a fixed return flow constant to be set for fuel systems that have a low volume return to the tank, thereby obviating the need for a second flow sensor and differential counter. If so it would be most useful to know how this is set. Is there some algorithm based on forward vs. return flow volume, or is it more complex than that?

 

[dynonsupport]

It's less complex than that. It assumes a constant return flow. You set it in "K" if I remember right, and it subtracts this amount of K from your flow sender.

So if your K factor is 30,000, that means 30,000 pulses per gallon.

If you expect a constant return to the tank of 1.5 GPH, then you would set this to 45,000 (30,000 * 1.5)

This will only work well if you have a fixed return orifice size and a fuel pressure regulator that is relatively stable.

 

[G3WGV]

Excellent, thanks very much. I've just spent most of the day (it's 7:30pm here in the UK) installing the D120 and it really is a nice piece of kit to work with.

 

[N439AT]

It's less complex than that. It assumes a constant return flow. You set it in "K" if I remember right, and it subtracts this amount of K from your flow sender.

So if your K factor is 30,000, that means 30,000 pulses per gallon.

If you expect a constant return to the tank of 1.5 GPH, then you would set this to 45,000 (30,000 * 1.5)

This will only work well if you have a fixed return orifice size and a fuel pressure regulator that is relatively stable.

I would like to resurrect this thread to ask if the RETRN FLOW parameter is only applicable if there is a second flow sensor in the system to measure return flow?

Tony

 

[dynonsupport]

No, it's to there to simulate a second fuel flow sensor being there on a EMS-D10/D120/D180 that always outputs the same theoretical fuel flow rate (not really what happens in the real world in many conditions, but it can be passable in some configurations). With those products, it is possible to measure the difference between the main fuel flow sensor and a 2nd actual fuel flow sensor for return flow via a Matronics box. SkyView can do it natively.

 

[PhantomPholly]

It's less complex than that. It assumes a constant return flow. You set it in "K" if I remember right, and it subtracts this amount of K from your flow sender.

So if your K factor is 30,000, that means 30,000 pulses per gallon.

If you expect a constant return to the tank of 1.5 GPH, then you would set this to 45,000 (30,000 * 1.5)

This will only work well if you have a fixed return orifice size and a fuel pressure regulator that is relatively stable.

I would like to resurrect this thread to ask if the RETRN FLOW parameter is only applicable if there is a second flow sensor in the system to measure return flow?

Tony

As they said, it's really a "manual correction." Ideally you will install the flow sensor downstream of any return line (if possible) so that what the sensor "sees" is the actual flow to the engine.