The function module determines the capacity of the valve. The module is a ready-made insert which is simply pushed into the valve body. It consists of a moveable control cone with V ports, and an orifice including the valve seat. The function module is manufactured using the most modern production techniques and guarantees a long, reliable life span with excellent control characteristics. It is sufficient to only exchange the function module to carry out a complete repair. This makes service easier and considerably reduces costs.