Quote:
Originally Posted by rpowers
While we're on the topic of the Facet fuel pump:
What does the pump do when the float reservoir is full and the float valve is closed?
It seems to keep on humming (pumping), but does it recirculate fuel within itself? I've opened mine up to look at the mesh screen filter, and there is a ball-valve in the center. Does anyone know what goes on inside?
Also, what is actually doing the pumping.
Is it a membrane or some other mechanism?
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My notes scavenged last year from various archived posts (I did not track the sources):
"FACET fuel pumps have a small diaphragm which moves the fuel under pressure. The pressure is internally regulated by a small spring-loaded by-pass valve that has been preset for the rated pressure of the pump. It is normal for the pump to keep on pumping (making a clicking sound) even when the carburetor is full and the pump is operating against a dead-head, or zero flow, condition." (Don)
"Facet pumps click when running. Fuel flow is regulated internally by a spring-loaded bypass valve, so that the fuel is recirculated internally when the pump's pressure set point is reached. They push not pull"
Some Facet pumps have a check valve that prevents fuel from draining through the pump if the pump is off and there is a downstream carb leak. but I don't think the usual model used in A4s has that feature?