A valve unit includes a valve housing having an input line and an output line or the process pressure as well as a process guide shaft, an operating piston for closing and opening a connection between the two lines, two control lines and two control chambers for controlling the operating piston. The operating piston has a closing ring which in the closed state of the connection sealingly abuts a valve seat of the valve housing and it has a diameter which corresponds to a guide diameter of a dynamic process seal. The valve seat includes a softer and more elastic material than the sealing edge. The valve unit has low axial forces, due to low sealing forces, thus makes a long service life with a high number of cycles of operation possible.