Sticky Throttle

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daves1459
Posts: 43
Joined: Mon Jun 07, 2010 7:58 pm

Re: Sticky Throttle

Postby daves1459 » Mon Aug 07, 2017 9:50 pm

Dan, If you look at the center photo you'll see a tongue of metal hanging down from the top and resting on the top edge of the valve. This is a piece of phosphor bronze spring material that presses the valve against the seat as it slides up and down under the spring.

The friction tables I have list the same values as you quoted. I have an ancient bronze bearing design book that lists smooth phosphor bronze on smooth phosphor bronze, dry, at .17. Certainly coefficient translates into the effort, but, as you point out something like Teflon or Vespel have near the same static and dynamic coefficient so should really help the stick slip issue. The valve is .218" thick. I can pocket it and drop in a wafer of material. I think I'll try the Vespel first as it is much easier to work with than Teflon.

Bill, It took me staring at the bottom side view of the throttle for a while before it hit me about the bottom link bending the rod as it is pulled and the link passes through and arc. The fact that the bottom link pivot point is not inline with the rod really aggravates the rod motion. I think with longer arm bell cranks and a straight bottom link the situation will improve.

Thank you to you all for your comments. I have some good ideas that will improve my situation. Unless someone has something to add I consider this thread complete.

Atkinson_Railroad
Posts: 88
Joined: Mon Jun 08, 2015 6:27 pm
Location: Michigan
Contact:

Re: Sticky Throttle

Postby Atkinson_Railroad » Tue Aug 08, 2017 6:05 am

This Properties Handbook published by DuPont has been helpful and have referred to it occasionally.
It's [roughly] 34 pages of just about everything you will ever need to know about Teflon PTFE.

http://www.rjchase.com/ptfe_handbook.pdf

John


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