|A western concert flute divided into many parts. (Photo credit: Wikipedia)|
This is achieved by seating the pads correctly and then bending the keys and testing them continually until you get the best seal possible. We test the seal in several ways. One of the most common ways is to use a strip of cigarette paper. You place it between the rim of the tone hole and the pad and then close the key to see if the paper is grabbed or slips out. If it slips out, that means that air can get out of that space and thus you will lose sound and volume etc. I use a jeweler's eye loop to examine the hole more than I use the cigarette paper because I can get a closer look through the magnification and I find it quicker.
Bending the keys to make them level was at first very scary. You are working on a $300.00 and up instrument and you're taking a pair of flute pliers and bending the key to insure it is setting right over the hole. Yes, you occasionally break the keys right off. At first this is very unnerving but when you realize that you are suppose to be able to fix keys that are broken off, then it becomes no big deal. Once you realize that all the pieces of the flute had to be made and soldered together, you can rest assured that you can fix anything. We have recovered flutes that have been stepped on, sat on, jammed in doors etc., etc.
Alright so we took out all dents and bends, which is a science all on it's own. We made sure the springs are all intact and of the correct tension. We have checked and replaced and seated all the necessary pads. Finally, we bent and leveled all the keys and their pads over the tone holes so that we get as close to a perfect seal as possible.
Then we clamp the keys shut, to make a deep imprint in the pad, thus making a very air tight seal. We do this by first using a small pad iron to iron out any wrinkles from any new pads. Then you soak the pads with alcohol (this is one method). Apply the individual key clamps. Then you place the flute in a pad oven for a few hours. Pad ovens vary in size and shape. I use a long narrow leak light, which I put in the flute and then I put it in a wooden box. Some people don't use an oven.
After that, you'll get a great seal and the flute will play great. The volume will be great with no hissing or leaks.
After that if you give it regular hand cleaning and have someone a tech give it a once over every 6 months you get the best out of your flute and it will last a long time.