Patent ID: 8567435

Claim:
A valve comprising: a valve body including a valve seat defining a fluid aperture and inclined at an angle from 5 to 35 degrees relative to a cross section of the valve body taken at 90 degrees relative to a fluid flow axis through the valve body; a valve head for contact with the valve seat for closure of the fluid aperture; a pair of elongate lever arms defining a longitudinal axis, each of the lever arms having a first end and an opposite second end, the first end of each lever arm being connected to the valve head, the lever arms being offset from the valve head, the lever arms being rotatable about a pivot axis located between the first ends and the second ends, the lever arms being symmetrically laterally spaced apart on opposite sides of the fluid flow axis to define an elongate space therebetween, the pivot axis being located in said space and said space extending on both longitudinal sides of the pivot axis; and an elongate tension spring having one end anchored to a first anchor point located between the second ends of the lever arms and an opposite end anchored to a second anchor point on the valve body, the elongate tension spring being configured to: (i) urge the valve head into contact with the valve seat on closure of the valve head, and (ii) provide a decreased opening force on opening of the valve head, wherein the first and second anchor points and the pivot axis, in combination with the angle of the valve seat, have a spatial arrangement that causes an acute angle made between a longitudinal axis of the spring and a longitudinal axis of the lever arms to decrease to less than 10 degrees when the valve head is fully opened, and wherein at least a portion of the spring is accommodated in the elongate space between the lever arms when the valve head is fully opened, said at least a portion of the spring extending on both longitudinal sides of the pivot axis.