Replacing Cork and Felt Bumpers
Putting on new cork and felt bumpers is really a job for an experienced repairman, but in an emergency you may have to do the job yourself. If regular cork bumpers are hot available, one can be made from an ordinary bottle cork. Clickless valves, be sure to glue on cork and felt with a glue not readily soluble in water, or saliva will soak them loose. Avoid getting any glue on the piston or casing walls, and be sure the slot in the cork and felt is centered so the pin will move up and down freely in this slot without touching.
Most valve stems are marked to indicate just how high the bu mper and felt should be to allow the piston to come up so that the ports in the pistons accurately meet the knuckles in the casing. If there is such a mark on the valve stem, it is easy to cut the cork so the piston will stop at the proper place when the finger releases it. Keep shaving or sanding off the cork until when you sight across the top of the valve cap, the mark on the valve stem is level with the top of the valve cap, then you know the cork and felt are the proper height.
If there is no such mark, you’d better let an experienced repairman do the job. It is extremely important that the height of cork and felt is correct, otherwise the ports in the piston and the knuckles in the casing will not meet accurately, and the instrument will blow stuffy and will lack resonance.