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

 

[alphy]

I can understand your difficulty in conceptualizing a mechanical mechanism to transmit the force from a centrifugal sensing device to a stop valve. It is a complex problem that requires a thorough understanding of mechanical engineering principles and design.

One possible solution could be to use a series of gears or pulleys to transmit the force from the centrifugal sensing device to the stop valve. This would require precise calculations and proper sizing of the gears to ensure that enough force is transmitted to effectively shut down the plant.

Another option could be to use a hydraulic system, where the force from the centrifugal sensing device is converted into hydraulic pressure and transmitted to the stop valve. This would require the design of a hydraulic circuit and selection of appropriate components such as pumps, valves, and cylinders.

It is important to consult with experts in the field of mechanical engineering to determine the most suitable and efficient solution for your specific application. They can also provide valuable insights and advice on the design and implementation of the mechanism.

In addition, computer-aided design (CAD) software can also be utilized to simulate and test the proposed mechanism, allowing for adjustments and improvements before actual implementation.

Overall, the successful design of a mechanical mechanism to transmit the force from a centrifugal sensing device to a stop valve requires a combination of theoretical knowledge, practical experience, and collaboration with experts in the field. I hope this helps in your understanding and approach to this problem. Best of luck in your endeavors.