Remove the pistons, wash them and the inside of the casings with mild dishwashing soap and warm water, and rinse in clean water. Be careful in handling the pistons that you do not drop or strike them against objects, as they are hollow and dent very easily. Wipe the pistons dry with clean cheesecloth and lay them on a clean cloth so they won’t pick up grit or dust. Then swab the inside of the casing with clean cheesecloth, using swab supplied with the instrument, or a weighted string. If you use the metal swab, be sure you do not gouge the casing wall with the end of the swab. Keep end covered with the cheesecloth. See Fig. 3 on how to do it. After cleaning, dip the pistons in clean, cold water and replace in the casings.
Be sure you get No. 1 piston in No. 1 casing, No. 2 piston in No. 2 casing, and No. 3 piston in No. 3 casing. This obvious point is stressed because it is so often a cause of trouble. The interchange of pistons one and 3 will still permit the instrument to be played but it will blow stuffy and will be out of tune. No. 1 casing is nearest the mouthpiece and No. 3 casing is nearest the bell; the pistons are numbered, usually on top; so there is no excuse for getting them mixed up. Sometimes the valve caps are also numbered 1, 2, 3, and if so be sure to avoid getting them mixed up, as they are liable not to be interchangeable. If the valve caps are numbered inside and should be properly replaced, No. 1 on No. 1 valve, etc.
On valves of the key-in-keyway type be sure you have the key properly started in the keyway before you push the piston down or the key and keyway may be damaged. In the spring barrel type valve , where various shapes and sizes of piston guides fit into slots in the upper end of the valve casting, be sure these guides are in their proper slots before you screw the top valve cap down. Sometimes these guides consist of 3 points irregularly spaced and sometimes they consist of one large and one small point. The reason for these designs is so the points of the guides will drop into the slots in the upper end of the casing in only one position, insuring proper radial location of ports in the piston with reference to knuckles in the valve casing.
On some valves there is a locating key in the pin head which determines the radial position of the piston; this fits into a short slot in the upper end of the casing, insuring that the ports and knuckles meet accurately. While the pistons and valve caps are not interchangeable and must be replaced carefully according to the number each bears, the pin heads are interchangeable. Be very careful in handling these pin heads that the pins do not become sprung or bent, for this will impair smooth valve action. If a pin does become bent or damaged, don’t try to repair it; get a new pin.