Rear engine fuel drains

[wslade2]

Agreed about the fuel strainer. I recently had a pesky drip that required replacement of the plunger.

[n86121]

I think I have them all traced correctly now.
Believe it or not, many transition to firesleeved hoses so it is a bit confusing!
Retracing a bowl of red spaghetti backwards from each end.

When mixture in detent. Cleanly shuts idle.
Is definitely in full idle against the stop.

Doesn't drip immediately on shut down, takes a while before ...drip drip drip.

Drip from LR cylinders definitely stops w fuel closed overhead.

Still drops with newly overhauled flow divider from QAA.COM.
Still drips after a while, and then endlessly.
Flow divider spec only supposed to hold 1 PSI for 2 mins.

Thinking what else could be seeping fuel into cylinders, ...I thought of hand primers...?

Noted from your comments,
I discovered (after 25 years) that hand primers have a lock position.
I have used them so rarely, I never noted the actual detent position before.
Generally I'd just push them in and twist, but apparently not locked.

Fuel back on.
We will see if drip resumes with primer in detent.

[Kim Geyer]

There is a check Valve in the engine driven fuel pump return line it could be faulty and allowing fuel back up thru the system. I’ve seen it twice on our planes

[n86121]

Looked up parts diagram and list
-40 check valve pump to manifold.
Will check that out.

Makes sense.

From the drawing
the check valve appears near / under the elec boost pump
In Engine compartment or inside firewall?
Hard to tell.

Will find it tomorrow.

Thanks!

[Kim Geyer]

On our T337H’s the check valve is under the headliner above the baggage door.

[n86121]

Found mine
Little red devil in front of rear oil cooler, oriented vertically
arrow down, into airframe (and I assume back to manifold and tanks)
Same?

Pulled, cleaned,
did a light sun n blow test.
Seemed OK
Re-installed.
No change.

That said, it relies on its internal spring to stay UP and closed, and spring is very weak.
So IN airplane might still drool?
So maybe replace anyway?
Later models they mount horizontally. Probably for that reason.

QAA.com says with mixture in idle cutoff,
light pressure in the flow divider and its check valve shouldn't really matter.
cutoff is cutoff.

Other ideas?

[wslade2]

crack the line going from fuel pump to "throttle" / flow control with mixture in off position, tank valve open. See if there is dripping. My expectation is there should be no flow (ie-cutting off the engine is achieved through no flow through the pump).

What I understand the purpose of diaphragm in the flow divider is, is to provide an "abrupt" cut off of fuel flow as the pressure drops from cutting fuel pressure via the mixture on the control on the pump. But it is not your "stop" of fuel flow. It just provides a clean break. Your pump should be the control that alters fuel line pressure or stops fuel flow.