Worn out Valves
The more worn the valves are, the worse the lower register plays. Often a worn-out valve on a trumpet for instance will still let you play high but when you try to go below the staff it becomes difficult to play.

1) Of course, it is hard to tell at a distance whether the valve has been severely damaged or not. But simply having the damage described is not a severe problem. Just because the wrong technique was used to try to remove it, doesn't mean that the right technique won't get it out without further damage.

2) valves and casings can be straightened out with the proper tools

3) slow and crunchy is wonderful description. Again, it is most likely a matter of aligning, polishing, and probably re-plating. The Hetman classic would be most effective on loose sloppy valves. Sounds like the problem with these valves lies elsewhere.

So, basically the process would be to remove the valves, straighten the valves and casings, and then if they are loosely fitting, replate them.

If the sound is bad just on depression of the valve, check the slide for leaks (or the spit valve).

Depressed piston valves of any type are likely to play poorer. Not only are leaky valves likely to cause airy sounds, but they also can be in places where bad nodes can cause intonation problems. Worn valves are just as likely to be leaky in either position; however, you have two more chances for leaks in the depressed position. This is then combined with the fact that you also have lots more joints which can cause leaks in a longer airway which is potentially "stuffier" to begin with. Compensating pistons in spades.

Worn Perinet valves can be helped with a thicker oil, but it is not a solution in the long run, more to find out about an instrument's other qualities. The thicker oil may make the valves sticky in cold weather, if you sometimes play outdoors. If the wear problem is only a minor, it could also be a solution for some time.

There are solutions to worn valves, but they are not just simple.

One method is copper plating, it is one of the simpler plating processes, and copper applies in a thicker layer than silver or nickel would do. It is necessary to stop the plating process several times, and polis the new copper layer, or it will get uneven. Note that some valve surface alloys may reject the copper plating.

A valve stem is being copper plated. The machine ensures a slow rotation while the plating goes on, to ensure a uniform layer on the valve. Sorry for the small pic.



The plate-and-polish goes on until the valve only fits sticky, then the valve is oiled and rubbed with a fine lap powder and moved in the valve house. Here it is good to remove guides that restrain valve movement, the valve should be able to move beyond its normal travel distance and rotate. Remove the valve, clean both valve and instrument, and see if the valve runs smooth, continue with the lap if it does not.

This process is demanding enough, so it is good to check if the instrument is worth the work, thick oil in the valves will do just fine.

Dealing with a valve cracked (and warped).

The cracks are tricky, why did they happen? Is there corrosion on the inside of the valve, or did someone try to free a frozen valve a little violently? Or is the material of an inferior quality? Metal, nicknamed "Crispbread brass" make the brass is very unstable and fragile.

This needs to be soldered with the appropriate solder (that’s a whole other topic). Then turned to round, copper plated to bring it back to close. Then turned again on a lathe, and final plating of your choice (nickel, silver or bronze).

If they're leaking, then you must have them plated. As part of the prep work, the cracks can be filled, but if there's not enough material to seal, the only way to add metal is plating.

Be very careful with solder to not disturb the fragile-looking through-tubes in the valves, nor the valves bodies, which must be VERY thin at those points.

Worn Valves
Let me first suggest a couple of different directions or preliminary steps in which to look at this problem.

I'd first suggest making sure that the issue is the play of the valves rather than, for example a leak somewhere else or an alignment problem.

I'd try to check that out by using a heavier oil on the valves. I use a mix of (traditional) valve oil [or lamp oil] and mineral oil. What you want to see is whether the sound improves, and at what point the action of the valves slows down. At 50% mineral oil or less, the valves can probably be managed with just using a heavy weight valve oil like Hetman's Classic.

If you need a higher % of mineral oil to get a good sound and the valves are still quick, then they are going to need to be rebuilt.

The next thing to consider is, are the valve casings still round? When the valves are rebuilt, they should be round, but if the casings aren't, then they still won't work well. One quick check is to put the pistons in the wrong casings and see how they work. And you can possibly also put them in from the bottom. You aren't necessarily going to learn anything conclusive, but you can get some clues.

The micrometers will have a role to play when it is time to decide how much to build up the pistons, but it is better not to rely on them too much. Correct clearance is better determined by the above than by measurement.

What you want to do is to determine what would be a tight fit for the piston into the casing. Then the lapping will open it up just enough for the piston to move smoothly within the casing.

I made that rotating apparatus because the plating process mainly takes place on the surface immediately towards the anode.

Then you may ask why not just deploy the calve inside a copper tube and keep the valve "standing" during the process?

Copper is quite heavy, the result is that during the process, the lower part of the valve will be plated with more copper than the upper part if done that way.

So, I made the rotating apparatus. The rotating speed is not essential, although the valve should at least make one turn in 5 minutes as very minimum, and as maximum not stir the solution in any way.

If there is need for a thick copper layer, the best result is obtained by plating some copper on, then polish the valve and hone it on "a suitable thing with a hole in it" (one you make of brass on purpose) - but not the valve housing! Then clean it and plate on and repeat as necessary. With very worn valves this process compensates that the valve is not worn alike all over its body but tends to become a little barrel-shaped by wear-off.

Only the final honing takes place between valve and valve housing.

And how much? That is a question of feeling. The valve should run smoothly, and will require very regular cleaning and lubrication during initial wear-in. The cleaning is important, lube alone doesn't do it!