Valve seat and valve

A valve seat for a ball valve in an adjustable medical valve is described. The valve seat is formed as a cone in a manifold. The cone is formed by rotating a line that intersects a central axis of the valve seat around the central axis. The angle of the intersection between the line and the central axis is doubled to form the included angle of the valve seat. Generally, the narrower the included angle, the better the tolerance of the assembled valve for variations in the spring constant of the pressure regulating spring. Specifically, the present invention has included angles between 0 and 90 degrees with the preferred included angles being between 10 and 40 degrees. A valve embodying the valve seat is also disclosed.