An adsorption dryer includes first and second drying towers (30, 32). Each tower has a first port and a second port through which gas can pass into or out of the tower. A first and a second manifold (34, 36) are connected respectively to the first and the second ports of both towers (30, 32). The manifolds (34, 36) each include integral gas passages (46, 48, 50, 52) each port of the towers (30, 32) being in communication with a gas passage. Each of the manifolds (34, 36) includes at least one integral valve seat (42, 44) upon which a valve actuator (72) is mounted to constitute a valve (V1..V6) to control flow of gas through the gas passages.