Patent ID: 6131882
Filing Date: 2000-10-17
Classification: F16K

Abstract:
A butterfly valve comprising:a stepped cylindrical valve body through which fluid flows, said stepped cylindrical valve body having a first diameter upstream portion, a second diameter downstream portion and a center line which extends coaxially through both of the first diameter upstream portion and the second diameter downstream portion;a sheet ring attached to the inner surface of said valve body, said sheet ring being located in said cylindrical body at a step between the first diameter upstream portion and the second diameter downstream portion, said sheet ring having an inner diameter essentially the same as a smaller of the first diameter upstream portion and second diameter downstream portion;a rotatable shaft which extends through a larger of the first diameter upstream portion and second diameter downstream portion so as to be rotatable about an axis which is offset from the center line; anda valve member of a generally disk-like shape secured to said shaft, said valve member having a first semi-circular half having a first curved sealing surface on an outer periphery thereof, and a second semi-circular half having a second curved sealing surface along an outer periphery thereof, said shaft and said valve member being offset from one another such that during a first initial rotation of said shaft through a predetermined small angle from a closed position wherein the first curved surface and the second curved surface are both in engagement with said sheet ring, the first half rotates towards the downstream portion, separates from the sheet ring and moves with respect to a wall portion of the second diameter downstream portion of the stepped cylindrical valve body to establish a small gap through which fluid can initially flow while the second half remains in contact with the sheet seal as it rotates towards the upstream side, and thus limit the amount of flow past the valve member to a controlled small amount and protect the sheet ring from damage by a sudden large change in flow amount.