At 10:02 PM 3/31/2001 -0500, Bud Krueger wrote:
> Can anyone lead me to a site with a good technical description of the
operation of the anti run-on valve circuit?
Well, noty right off hand, but it's easy enough to explain. The anti
run-on valve is used to apply manifold vacuum to the float chamber of the
carburetor when the ignition switch is turned to the OFF position to stop
the engine. Drawing a vacuum on the float chamber effectively stops fuel
from flowing into the jets of the carburetor, so the engine dies
immediately with no running on.
This is accomplished electrically as follows. There is a terminal on the
ignition switch that is turned on (hot) when the ignition switch is turned
to the OFF position. This power is routed through the anti run-on valve
solenoid and then on to an oil pressure switch on the engine. The oil
pressure switch maintains a grounding connection with oil pressure, but
goes open circuit when the oil pressure drops.
So when the engine is running the oil pressure maintains the ground
connection. Then when you switch off the ignition switch supplies the
power to trigger the anti run-on valve, which stops the fuel and kills the
engine quickly. When the engine stops turning the oil pressure drops and
the pressure switch opens, which removes the ground connection and releases
the anti run-on solenoid so it won't run the battery down when parked. As
such, electrical power is only applied to the anti run-on valve from the
time you switch off until the engine stops turning. The rest of the time
the float chamber is vented to atmosphere.
Barney Gaylord
1958 MGA with an attitude (and no anti run-on valve)
http://www.ntsource.com/~barneymg
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