Transmitting link for overspeed trip.

[xandro101]

I am a newly graduated mechanical engineer and I have difficulty conceptualizing what sort of strictly mechanical mechanism I could use to transmit the force available from a centrifugal sensing device at the main shaft of a prime mover all the way to a stop valve to shutdown the plant. I need a little assistance from experts in this forum.

 

[AlephZero]

Think of something that is so simple it can't possibly fail.

A nice strong metal chain or wire, with one end attached to a mechanical governor and the other end pulling a fuel shiutoff valve closed, would be one option. Some jet engines have exactly that as the "ultimate" safety device, in case the electronic systems that control normal engine operation fail.

 

[DickL]

If the stop valve is a solenoid valve, then having the centrifugal sensing device open a contact in the valve's solenoid circuit is the simple means, assuming the valve is a normally closed valve (energize to open).

If it is a motor controlled valve, tripping a contact would still work, except the resulting action would be to command the motor to close the valve.

If the stop valve is more than a short distance away from the cf device, a purely mechanical means would probably become a questionable solution.

 

[Bob S]

Take apart a typical single-phase fractional-horsepower induction motor (e.g., 1840 RPM in the USA) and look at the centrifugal switch to disconnect the starting coil. This an electrical contact.

Now look at the starting circuit for a single phase repulsion-start induction motor, which mechanically disconnects the stationary brushes from the rotating radial commutator above a set RPM. The mechanism is a centrifugally-actuated hollow tube that slides axially on the motor axle. See picture thumbnail of radial commutator on a pre WW I induction motor.
motor.

[added] Manufactured by Century Electric about 1914. See also http://www.flickr.com/photos/47938537@N02/5118932181/

Bob S