Double-seal flexible gate valve

A gate valve for controlling flow in an axial direction, comprising:

• an axially-extending valve body having a discharge orifice of preselected diameter;
• a gate assembly including a spacer disk, a rigid backup plate of diameter substantially less than that of said discharge orifice joined to upper and lower flexible sealing disks spaced apart by the spacer disk, each of said sealing disks having an outer diameter greater than that of said backup plate and of said spacer disk;
• valve seat means comprising radially inner and outer annular valve seating rings, with said inner ring having a sealing surface below that of said outer ring so as to be offset therefrom, said rings attached to said valve body adjacent said discharge orifice for sealingly engaging said sealing disks such that the upper sealing disk forms a pressure-tight seal with said outer ring and a separate pressure-tight seal is formed with said lower sealing disk and said inner ring, the upper and lower sealing disks being deflected when seated against the seating rings so as to have concave configurations for achieving a wiping action across the sealing surfaces which is defined by the offset of said sealing rings;
• valve positioning means for moving said backup plate in downstream and upstream directions so as to bring said upper and lower sealing disks into and out of engagement with said outer and inner valve seat rings, respectively;
• and
• said valve seat means defines chamber means between the pressure-tight seals formed with said upstream and said downstream sealing disks, for receiving seepage flowing past at least one of said seals.