Re: Valve Springs


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Posted by John Swensen on January 14, 2000 at 15:59:34:

In Reply to: Valve Springs posted by Tim Cary on January 13, 2000 at 16:27:36:

Springs for piston valves are usually made of bronze wire, but could be stainless steel for some models. There are lots of variables to play with to determine a spring's characteristics, including wire material, wire diameter, spring diameter, number of turns, taper of spring (if any), end treatment, and others. Some valves (such as the Nirschl valves on B&S, VMI, Nirschl, Hirsbrunner (and other?) tubas) have small cups in the piston bottoms and bottom valve caps that pretty much limit the outside diameter of the spring, but you could play around with the other variables to find a spring "feel" that you like.

For rotary valves the spring wire could be either music wire, bronze wire, or stainless steel wire, and the constraint here is the inside diameter of the spring. Clocksprings in old Alexander and B&S tubas and new St. Petersburgs, are usually flat (spring) steel.

The good news is, if you are reasonably handy, it is easy to wind your own wire springs with minimal tooling, using instructions found at this site (clocksprings require some more extensive tooling, any may be beyond the casual tinkerer). You can find bronze wire (around .036" is about right for Nirschl valves) from a harpsichord string supplier (I have been very happy dealing with The Instrument Workshop, in Ashland, Oregon), and music wire from a hobby shop is an easily-available source for quick experiments. After winding the springs, you bake them in your oven for about a half an hour to stress-relieve them (they tend to unwind, otherwise). I have made several sets of rotary-valve springs (in music wire and bronze) that have allowed me to adjust the resistance of the keys. One word of advice is to wind the springs on a steel mandrel (brass is way too soft), and, again, music wire comes in a range of diameters suitable for rotary keys.

You can always put the old springs back if your new springs don't work out, so there is nothing to be lost by experimenting.



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