Posted by David on May 20, 2001 at 09:00:32:
In Reply to: Question out of left field! posted by Rick on May 19, 2001 at 08:06:42:
The valve guides currently on instruments are made out of delrin, the same stuff as found on some timing chain sprockets in small cars. Delrin is very sturdy. The reason it wears out has nothing to do with the material. It has to do with "how" a person puts the valve back in the valve casing. If you will spin the valve carefully until the valve guide lines up with the slot, not get in a hurry, and slide the material into the slot, it should last a very long time. Another tip to make them last longer is to "never" tighten the finger button with the valve in the casing. This puts sideways pressure on the valve guide and will eventually shear off the material on the metal slot.
Delrin would be a perfect choice if a plastic material were used. It is impervious to all the heat and all oils. The experience manufacturers have had, however, would probably make them shy away from anything called 'plastic'. Teflon does eventually wear off, polypropolene is subject to expansion in the heat, and nylon expands when oil gets on it as it absorbs the oil.
The question of a lighter valve has been around for at least 40 years, and maybe more. Manufacturers, and some individuals, have experimented with hollow rotors or even drilling holes in them. (Drilling holes 'tends' to build up heat causing the rotor to expand. They don't fit very well after that!!!! I had a friend try that routine one time. It's really expensive to replace all the rotors!!) The first plastics (?) to come out were not nearly as good as the stuff made today. As I said before, nylon expands with oil - not a good choice, polypropolene (the lightest one) expands and contracts with heat and cold, but DELRIN....If a manufacturer could be convinced 'we' would buy the concept, one of them might give it a go.
Personally, I am going back to the metal valve guides which your local repairman can get from UMI, Allied Suppy, or Badger State Supply as King sousa valve guides (let the repairman choose where to get the valve guides - it'll save you a bigger bill later). They are threaded so the hole in the valve also has to be threaded. A good repairman has the taps and dies to do such a job. The valve guides will have to be filed down to fit exactly and "please" let the repairman do this.
Most of the "new" valves are made out of stainless steel with brass inserts on the tubing with delrin valve guides. By putting in lighter springs, and making sure the valves are kept clean and oiled the valves should last a very long time and perform very well.