[Vlad]

I have a carbureted 320 and can not answer somebody's question about fuel injection. He is asking what is this fitting for

Engine is IO-360M1B.

 

[cfiidon]

The technical name eludes me (someone help here), but it's a fuel overflow thing-a-ma-bob. Ideally, it should have a tube from it to somewhere safe... but I note that the one on my Bonanza has nothing.

Don

 

[[email protected]]

tap for fuel flow gauge

it looks like the port for picking up fuel flow on a gauge.

 

[Kahuna]

it looks like the port for picking up fuel flow on a gauge.

All wrong.
You cant measure total engine fuel flow out of a spider port.
It was likely used for fuel pressure gage.
It could be removed and plugged.
It is not a "overflow thingy" either.

 

[[email protected]]

hmmmmm...

i was under the impression that fuel pressure and flow in the spider are linear and the port was used for direct read gauges to indicate fuel flow from the pressure...

 

[cfiidon]

Careful!

All wrong.
You cant measure total engine fuel flow out of a spider port.
It was likely used for fuel pressure gage.
It could be removed and plugged.
It is not a "overflow thingy" either.

My ECi documention labels it as a vent. From an AVWEB article on fuel injection it says:

"The upper side of the divider diaphragm is vented to atmospheric pressure. A small hole will be drilled in the manifold valve-cover to allow for this venting, or a fitting will be installed to provide for a drain-line attachment. Any blockage of this vent will result in a fuel flow loss at altitude, due to the expansion of the trapped air within the cavity as the aircraft climbs. When the air expands against the diaphragm, the valve is forced downward against its seat, effectively closing off fuel flow through the valve."

So blocking/plugging this would be a very bad idea....

 

[aerhed]

All wrong.
You cant measure total engine fuel flow out of a spider port.
It was likely used for fuel pressure gage.
It could be removed and plugged.

Yer wrong too.
There should be a fitting for a drain above the diaphragm. Drains overboard in case of diaphragm failure. Also planes like Cessnas use a port in parallel with the injector line outputs to measure "fuel flow". It's actually just a calibrated pressure gage that equates manifold valve pressure with flow.

 

[Neal@F14]

Could it be a fitting for connecting to a purge valve?

 

[Don at Airflow]

What the "gage" port is really for.

Back in the day before all the cool electronic stuff was available, things had to be done mechanically. Some of you may recall flying a Piper, Mooney or Beechcraft with a split Manifold pressure/Fuel Flow gauge on the panel. The fuel flow gauge was connected to the ?gage? port on the flow divider. The ?gage? port was cross-drilled into the adjacent nozzle line port, so the pressure it read was injector nozzle backpressure. Since the nozzle size and amount of nozzles on an engine is a known factor a relationship can be established between injector nozzle backpressure and total fuel flow. Granted this relationship is based on a square curve (since the nozzle has a fixed orifice) therefore the pressure vs. fuel flow is not a linear function on the pressure gauge. In most applications the nozzle backpressure at max fuel flow is around 7 to 10 PSI, so fuel flows at idle and in the lower power ranges are not very accurate or un-readable. But in any case manufactures could re-face a pressure gauge to read fuel flow.

Today with most homebuilders using electronic engine data capture a ?turbine? type flow meter is used. In these cases the ?gage? port on the flow divider should be plugged or the fitting capped. The ?gage? port is some times a useful in troubleshooting for picking up clogged injector nozzles.

Don