Stack mold transfer device are disclosed that include first and second transfer members having respective first and second transfer channels, first and second valve seats, and first and second valve members. The first valve member defining a flow portion and a first sealing surface and the second valve member defining a second sealing surface and a receiving pocket. When the first and second transfer members are in an engaged configuration, the first and second transfer channels form a common transfer channel. When the transfer device is in a closed-flow configuration, the flow of molding material is blocked, and when the transfer device is in an open-flow configuration, the first sealing surface of the first valve member is slidably received in the receiving pocket of the second valve member and the flow portion of the first valve member is positioned to allow molding material flow within the common transfer channel.