Before each playing the clarinet (practicing, preparing for the clarinet lessons, rehearsals with the piano accompaniment, public appearances, etc…) you should check its playing condition in order to remove the eventual malfunction promptly.

           It is impossible to play on a defective instrument.

So, check the following:

1.  Are all the screws in the mechanic in place and whether they are properly tightened?
2. Are all the needle-springs and the springs in place and whether they are correct?
3.  Are the holes of the upper and lower joint clean?
4.  Are all the pads in place and whether they properly close the holes and are not worn out?

    This checking is done by taking the upper joint of the clarinet in the left hand and covering all the holes, as when playing tone c1. We close the lower hole of the clarinet pipe with the right palm and blow powerfully several times through the upper opening to make sure that the air does not come out through any pad (see picture left).

    We do the same checking with the lower joint of the clarinet. The difference is that we here use the right hand when closing holes. We then press the key 1a with the little finger, and close the lower hole of the clarinet pipe with the left palm (see picture right).

      If you have checked that the air does not come out anywhere, and pads cover the holes well the clarinet is in good playing condition!

Taken from my book
I Am Studying Clarinet I