Valve device, in particular a pig loader, for joining to a thick-matter conveying line of a construction machine for conveying thick matter, wherein the valve device has: - a base body and an, in particular slide-like, adjustment body, which is adjustable relative to the base body between a first switching position and a second switching position, and - an automatic, in particular active, transfer device (4, 4A) with a receiving space for receiving a media separation device (M, M1), in particular a pig, - wherein the base body has a first connector for connection to a pump side of the construction machine, in particular to a pump-side thick-matter pump line of the construction machine, through which pump line thick matter is able to flow, and has a second connector, - wherein the adjustment body has a third connector for connection of the thick-matter conveying line of the construction machine, - wherein the second connector and the receiving space are connected to one another, - wherein, in the first switching position, the first connector and the third connector are connected to one another for a flow at least of thick matter between the first connector and the third connector, - wherein, in the second switching position, the second connector and the third connector are connected to one another for automatic transfer of the media separation device (M, M1) between the third connector and the transfer device (4, 4A), in particular via the second connector, characterized in that - the transfer device (4, 4A, 4B) has a piston which is guided in the receiving space so as to be adjustable relative to a housing of the transfer device (4, 4A, 4B) in such a way that, in particular in the second switching position, the media separation device (M, M1, M2) is transferable from the receiving space by adjustment of the piston relative to the housing, in that - the piston is adjustable relative to a housing of the transfer device (4, 4A, 4B) between a first and a second piston position (S1, S2) along an adjustment direction, in that - the piston, in the first piston position along the adjustment direction, is arranged at a distance from the connector (K2, K4, K5) that is connected to the receiving space, and in that - the piston, in the second piston position along the adjustment direction, is received in the respective connector (K2, K4, K5) in such a way that this connector (K2, K4, K5) is separated in a fluid-tight manner from the receiving space by means of the piston. - a base body and an, in particular slide-like, adjustment body, which is adjustable relative to the base body between a first switching position and a second switching position, and - an automatic, in particular active, transfer device (4, 4A) with a receiving space for receiving a media separation device (M, M1), in particular a pig, - wherein the base body has a first connector for connection to a pump side of the construction machine, in particular to a pump-side thick-matter pump line of the construction machine, through which pump line thick matter is able to flow, and has a second connector, - wherein the adjustment body has a third connector for connection of the thick-matter conveying line of the construction machine, - wherein the second connector and the receiving space are connected to one another, - wherein, in the first switching position, the first connector and the third connector are connected to one another for a flow at least of thick matter between the first connector and the third connector, - wherein, in the second switching position, the second connector and the third connector are connected to one another for automatic transfer of the media separation device (M, M1) between the third connector and the transfer device (4, 4A), in particular via the second connector, - the transfer device (4, 4A, 4B) has a piston which is guided in the receiving space so as to be adjustable relative to a housing of the transfer device (4, 4A, 4B) in such a way that, in particular in the second switching position, the media separation device (M, M1, M2) is transferable from the receiving space by adjustment of the piston relative to the housing, in that - the piston is adjustable relative to a housing of the transfer device (4, 4A, 4B) between a first and a second piston position (S1, S2) along an adjustment direction, in that - the piston, in the first piston position along the adjustment direction, is arranged at a distance from the connector (K2, K4, K5) that is connected to the receiving space, and in that - the piston, in the second piston position along the adjustment direction, is received in the respective connector (K2, K4, K5) in such a way that this connector (K2, K4, K5) is separated in a fluid-tight manner from the receiving space by means of the piston.