A musical instrument piston valve receivable in a valve casing. The valve includes a valve stem, a valve barrel connected to the valve stem, and a valve guide slidably disposed with respect to the valve barrel. A spring is disposed in the valve barrel extending between the valve stem and the valve guide. A piston extends from the valve barrel and includes one or more ports. There are also various ways of adjusting the angular orientation of the piston in the valve casing. It is preferred that the piston and the valve barrel are monolithic in construction and the piston valve includes an adjustable valve guide.