A sealing arrangement for a quad sector rotary regenerative air preheater (10) has a rotor (12) rotatably mounted in a housing (14). The rotor (12) has radially extending diaphragms (16) forming compartments (17) and radial seals (66) extending along the edges of the diaphragms. Sector plates (30) are positioned at the axial ends of the rotor (12) to divide the preheater (10) into a flue gas sector (34), a primary air sector (40) and a first secondary air sector (42, 44) adjacent said flue gas sector (34) and said primary air sector (40), and a second secondary air sector (42, 44) positioned adjacent said flue gas sector (34) and said primary air sector (40). The sector plates (30) between the flue gas sector (34) and said secondary air sectors (42, 44) are in sealing engagement with two of the radial seals (66) at all times and the sector plates (62, 64) between the primary air sector (40) and the second air sectors (42, 44) are in sealing engagement with only one of the radial seals (66) at any particular time.