Freeing Stuck Valves and Valve Caps

This isn’t as large a topic as some I’ve covered, but very important, especially if I can help you avoid major damage that is often caused while attempting to free stuck valves. I’ll start with that.

First, I’ll address stuck valve caps. Most often this is very simple, although in extreme cases, can be a challenge.  First, never use plyers, which will cause damage to both the caps and casings.  The best way is using a cowhide or wooden mallet, lightly tap around the circumference and try unscrewing it again.  If not successful, try again, tapping a little harder and in the direction that they will unscrew, but very careful not to damage anything.  Next, try tapping while trying to unscrew.  Again, be careful not to hit too hard or hit the casing, which would damage it.  Next, with the pistons removed, but bottom caps still stuck, use a tapered punch that fits in the hole in the cap, use the thumb and finger of one hand on the cap and grip the punch with the other hand and turn.  This will almost always do the job, but if not, use heat at the same time and add a little penetrating oil.  Don't heat the brass more than that which would volatilize the penetrating oil.

Using a combination of the steps above will eventually loosen the most stubborn cap.

The next photo shows two pistons that have been punched through from the bottom, the first with a screwdriver and the second with a wooden dowel. While this sort of damage can be repaired, the cost is more than most instruments are worth. In the first case, the screwdriver gouged the casing as well. Of course, in current production instruments, the piston might be replaced with less expense.

In the second photo, the bottoms of the pistons have been battered, but they got lucky or used judgement to stop before ruining them. If the pistons were freed with this amount of force, they really weren’t stuck badly. Sometimes the pistons are still deformed by this force and still need to be repaired in order to function.

There are several causes for pistons to stick, by far the most common being dried spit. This only happens from gross neglect of minimal maintenance. If the instrument is never cleaned or lubricated, eventually enough minerals are deposited and allowed to dry out, cementing the piston in place.

The second is from solidified oil. This doesn’t happen to modern (last 80 years or so) valve oils. They will evaporate completely or at worst, thicken only enough to slow the valves down. Vegetable and animal oils can oxidize and eventually become solid, locking the valves or slides in place.

The third is damage to the casing that is bad enough, either a dent or bend, to bind the piston.

The last is an obstruction in the bore, bridging the piston and casing ports.

I’ll address these in reverse order:

In the case of an obstruction, the most common being a paper clip that has gotten into the bell and found its way to the first valve (usually). The valve will move up and down only a little, but can’t be depressed all of the way or withdrawn. Forcing it will badly damage both the piston and casing as was done by the screwdriver above. The only solution is to remove the obstruction before removing the piston. Sometimes it is loose enough that it can drop away by its own weight. If not, you will have to be very creative and cautious in getting this to move. Sometimes, I’ve been able to free it up using a small dent ball on a right angle rod intended for removing dents from knuckles. Insert it into the second valve casing, assuming the obstruction is in the third and gently push towards the bell, where it entered. A similar tool could be made from plastic or aluminum.

I’ve also had luck dropping a brass dent ball driver into the bore from the other direction. Be absolutely sure that it is small enough to go though the ports or you will add another obstruction and be gentle so that it won’t wedge itself beside the paper clip.

The last option that I have used (this could easily be the first choice) is to insert a cleaning snake through the lower tube of the third valve (this works in most modern trumpets and cornets). Snake it through the third and second casings and gently push against the obstruction. Once again, there is danger that it will wedge beside it or go past, but a little finesse should get results.

A damaged casing will also bind a piston. Often, the second valve slide has been bent towards the first valve, distorting the casing. The slide can usually be pulled back enough to withdraw the piston and then the damage can be repaired. Sometimes the whole valve section is bent, with the braces and knuckles between the casings causing the binding. Again, it can usually be at least partially bent back, just using your hands (apply your knee with great caution), allowing the valves to be removed. Often, the piston(s) is/are also damaged, so both it/they and the casing need repair. Any of the casings can be dented causing the piston to bind. Obviously, the dent can’t be repaired with the piston in place, so it must be pulled free, regardless. Sometimes there is no consequential damage to the piston, but often there is and it must be repaired.

Probably the most common damage to a piston valve casing is at the very bottom, when the instrument is dropped or hit hard on the bottom cap. In this case, the piston will travel down freely until it hits this damage and then stick. This is actually the easiest to repair. Pull the piston out, remove the bottom cap and insert a tapered dent mandrel through the bottom of the casing. Push and twist this cautiously, withdraw and try the piston. If it still binds, go a little further with the mandrel. In rare cases, the bottom threads are expanded enough to bind the bottom cap. This will need to be repaired separately, so caution may save you time and/or expense.

It is rare to find a modern instrument with solidified oil causing the problem, but occasionally, somebody applies vegetable oil and with enough time, it will cause the pistons to stick solid. This usually requires the application of heat, enough to be just uncomfortable to hold, to soften the oil enough to withdraw the pistons. If enough decades have passed, it may take more heat. I believe that I’ve had to get the casings hotter than 300 degrees Fahrenheit before the oil softened enough, in one or two cases during my career.

The last is by far the most common situation, with buildup of minerals, cementing the pistons in place. This is also the most common cause of stuck rotary valves. With these it is best to remove them by normal methods, clean thoroughly and re-install with fresh oil. Most often with piston valves, this is slight enough that they can be pulled out by hand. If they don’t come out fairly easily, apply valve or penetrating oil where ever you can get to to the edges of gaps. A bit of heat can also help at this point. If this doesn’t get them moving, remove the caps and buttons. Again, get oil where you can and apply enough heat that it is just uncomfortable to hold. With a hyde, wood or plastic mallet, tap the top of the valve stem gently until the piston just starts to move. Install the valve button again and pull. If it won’t move, apply a little more heat and tap just a little harder. Use your best judgement, keeping in mind that you are working on brass that is easily damaged. Don’t use too much force and don’t be tempted to drive it up from the bottom. You can insert your little finger into the bottom of the casing while pulling on the button. On occasion, I’ve removed the stem and installed a lapping handle on the piston. Then with oil and heat applied, I can lightly tap the handle both down and up until the piston starts to move. Once it starts moving, it almost always comes out easily.

Almost as a post script, I’ll add another case that should never happen, but a repair shop that deals with school instruments will likely experience eventually. Some teenagers and pre-teens have troubled lives and may think that there is some reason to apply cyanoacrylate adhesive to a band mates valves. This can be softened with heat, but it takes about 500 degrees Fahrenheit, which will melt solder with predictable results.