The most important maintenance task relates to pads -- they must be seated precisely in order to seal completely.

Perfectly seated pads are necessary in order for the instrument to respond clearly and immediately.

Pads must seal by virtue of being airtight, not through the stiffness of spring tension.

Each pad must close exactly parallel with the tone hole, covering the entire circumference of the hole at exactly the same moment.

A clarinet that leaks due to improper sealing of pads, joints or cracks will be more resistant than an instrument that seals tightly. When selecting a new instrument you must learn to tell the difference between the natural resistance of the wood and the
unnatural resistance produced by improper sealing.

Here is a test that the player can apply to see whether pads are absolutely tight:

When all the holes in each joint of the clarinet are covered by the pads and moistened fingertips, the lower tenon is pressed against the moistened palm of the other hand to make an effective seal, and suction is applied to the top tenon by the mouth and held by the inside of the upper lip. A perfect vacuum should then be created inside the bore. If the clarinet does not suck up tightly in this manner, then it leaks and must be adjusted.

Sealing the holes, blowing air through the tube and listening for the hiss of leaking air does not test effectively whether the clarinet is tight. The clarinet must be made to hold a strong vacuum, especially the upper joint.

The upper joint, as well as the first two pads on the lower joint, should be entirely sealed by cork pads. The remaining tone holes are too large to be sealed by cork pads and must have skin pads.

Cork pads seal tightly but are slightly noisier in operation than skin pads. However, this can--and should--be compensated for by perfection of spring tension in combination
with an impeccable legato finger action. For a cork pad to seal properly, it must be shaped to fit precisely over the tone hole, with no imperfections in the cork--especially the part of the pad coming in contact with the rim of the tone hole.

Skin and/or leather pads may close silently, but are often the major cause of leaks. For a skin pad to seal correctly, it must be airtight in its construction. The skin must not be attached too loosely over the material of the base or a leak will result. The skin must
neither be stretched so tightly that the pores are spread apart thereby initiating a leak.

As with the clarinet itself, a skin pad must be tested for leakage through vacuum suction. This can be done by utilizing a tube of the same diameter as the tone hole, placing it directly on the pad, and attempting to create a vacuum through oral suction. The majority of pads will be discovered to be unsuitable.

It is important that the lowest pads on the right-hand side of the lower joint close precisely together. As time goes by, these pads tend to bind on the upper edge and must be readjusted to prevent leakage. Each pad must open to exactly the correct
height for purposes of intonation and tone quality. As shown in the drawing on the left, if the opening is too small the tone will be flat or muffled. If the opening is too big, as shown on the right, the action will be too slow and the sound will be too bright.

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