A method for operating an inline coating installation comprising - an introduction chamber with an insertion gate, - a first buffer chamber adjoining the introduction chamber, which can be separated from the introduction chamber by means of a first insertion gate, - a process chamber adjoining the first buffer chamber, which can be separated from the buffer chamber by means of a second insertion gate, - a second buffer chamber adjoining the process chamber, which can be separated from the process chamber by means of a third insertion gate, - a discharge chamber adjoining the second buffer chamber and having an outlet port, which can be separated from the second buffer chamber by means of a fourth insertion gate, wherein the introduction chamber, the first buffer chamber, the second buffer chamber and the discharge chamber are designed as a module for receiving substrates up to a predetermined size, wherein the substrates for the coating are transported from the introduction chamber through the first buffer chamber to the process chamber and from the process chamber through the second buffer chamber to the discharge chamber, characterized in that the first buffer chamber has a gap sluice device with at least one slit diaphragm by means of which, when the first insertion gate is open or closed, within the first buffer chamber a pressure gradient is adjusted between the pressure in the region of the second insertion gate and the pressure in the region of the first insertion gate and in that also when the insertion gate is open and the first insertion gate is open, a pressure gradient between the pressure in the region of the second insertion gate and the pressure in the region of the first insertion gate is maintained by operating pumps connected to the buffer chamber within the buffer chamber. - an introduction chamber with an insertion gate, - a first buffer chamber adjoining the introduction chamber, which can be separated from the introduction chamber by means of a first insertion gate, - a process chamber adjoining the first buffer chamber, which can be separated from the buffer chamber by means of a second insertion gate, - a second buffer chamber adjoining the process chamber, which can be separated from the process chamber by means of a third insertion gate, - a discharge chamber adjoining the second buffer chamber and having an outlet port, which can be separated from the second buffer chamber by means of a fourth insertion gate, wherein the introduction chamber, the first buffer chamber, the second buffer chamber and the discharge chamber are designed as a module for receiving substrates up to a predetermined size, wherein the substrates for the coating are transported from the introduction chamber through the first buffer chamber to the process chamber and from the process chamber through the second buffer chamber to the discharge chamber, characterized in that the first buffer chamber has a gap sluice device with at least one slit diaphragm by means of which, when the first insertion gate is open or closed, within the first buffer chamber a pressure gradient is adjusted between the pressure in the region of the second insertion gate and the pressure in the region of the first insertion gate and in that also when the insertion gate is open and the first insertion gate is open, a pressure gradient between the pressure in the region of the second insertion gate and the pressure in the region of the first insertion gate is maintained by operating pumps connected to the buffer chamber within the buffer chamber.