Re: Re: New Article on Valve Linkages


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Posted by Rick Denney on March 08, 2004 at 11:42:39:

In Reply to: Re: New Article on Valve Linkages posted by one thought on March 08, 2004 at 11:18:26:

Yes, I've done that when needed. But it makes measurement more difficult--you can't remove the sleeve after making the bend. It's best to do a little math to see how much longer it needs to be, and then make all four linkages longer. Then bend them all at once, and if it turns out wrong, start over, heh, heh.

As to the forces involved, it makes no difference. I know it seems like it should make a difference, but it doesn't. In engineering and physics, we draw free-body diagrams to look at those forces, and the free-body diagram remains the same. With the bent rod, the force will still be applied on the underside of the ball surface, in line with the other hinge. This happens with S-linkages, too, where the top side of the S-link wears more than the bottom side because the linkage geometry is pushing up on it. The only way to eliminate off-axis force on the stop arm is to raise the linkage so that the joint on the lever is in the plane of rotation of the stop arm joint. This is how string linkages were set up. But I doubt it matters much.

There's no worry of the tube rattling between the joints. The plastic is soft and allows solid tightening against the brass. I've never had them work loose.

Rick "who bends the arms when needed to provide clearance between the joint and the stop arm" Denney


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