Posted by John Swensen on June 22, 2000 at 18:27:41:
In Reply to: Re: Re: Re: Re: Questions posted by Klaus on June 22, 2000 at 16:54:26:
Klaus,
Here, alleviated means "solved".
Using crude ASCII graphics, a spindle and bearing looks like this:
-/ \- This is the bearing
__/\__ This is the spindle, where it fits in the bearing
The spindle has a tapered top, plus a flat flange around the bottom of the taper, and the bearing has a matching tapered hole, plus a flange that meets the flange at the bottom of the spindle. When correctly fitted, the flanges are in close contact, with the bearing taper just slightly larger in diameter than the spindle taper. You can see that, if the spindle is moved down, relative to the bearing, the fit of the bearing becomes looser, and if it is moved up, the fit becomes tighter. With a new rotary valve, the flange prevents the rotor from moving too far up, and the bottom bearing keeps the rotor from moving too far down.
There is a similar taper at the bottom of the rotor, where the bottom spindle engages with the bottom bearing. Getting the top and bottom bearings to fit just right requires some precision machining.
As the bearings wear over time, ideally the flanges wear just enough, relative to the spindle, that the fit of the tapers remains close, but free-running. Unfortunately, the overall distance between the top and bottom bearing flanges remains fixed, over time (it can even increase, slightly, with wear of the flanges). This could be corrected by periodically remachining the bottom bearing plate to fit closer to the top bearing, but a more common solution is to put a screw in the bottom valve cap, pushing the entire rotor up slightly for a good fit at the top bearing (where the majority of forces act), with a looser fit at the bottom bearing. The adjustment screw sometimes acts like an additional bearing, keeping the bottom spindle aligned.
To state it a little more directly, the screw can take up some slack in a worn bearing, but it does not expand anything.