Trumpet valves are made up of a finger button, valve stem, top cap, valve spring, valve guide and piston. Inside the casings are notches that receive the valve guides and allow the valves to be depressed. The notches and guides are sized so that the valve can fit properly only in one orientation. Each piston has a number engraved on one side above the valve guide. This number helps ensure the valve is inserted in the proper hole and in the correct orientation.
Locate the first valve. It will have a numeral "1" engraved above the valve guide. Insert it in the valve casing closest to the mouthpiece. Turn the valve until the numeral "1" is facing the mouthpiece and the valve guide drops into its notches. Tighten the top cap.
Insert the valve with the numeral "2" into the middle casing. Rotate it until the the numeral "2" faces the mouthpiece and the valve guide fits into its notches. Tighten the top cap.
Slide the final valve into the casing closest to the bell. Rotate it until the numeral "3" is facing the mouthpiece and the valve guide rests in its notches. Tighten the top cap.
Press each valve individually to make sure they slide smoothly and easily.