Adjustable loss-of-head valve

Claim 1

An adjustable loss-of-head valve for clamping between two opposed flanges of a pipe, said valve comprising: an annular body of a diameter permitting said body to be clamped between said pipe flanges, an annular recess on the inner periphery and to one side of said annular body and defining a upstream annular constriction and forming a first radial shoulder and wherein said annular recess includes a radially projecting portion on the downstream side of said annular body and forming a second radial shoulder downstream of said first shoulder, a stationary perforated plate having a diameter in excess of the internal diameter of said annular constriction and positioned within said recess and having a radially projecting portion in abutment with said second shoulder such that the upstream end thereof is spaced axially from said first shoulder, a mobile perforated plate having a diameter less than the diameter of the recess but greater than the diameter of the annular constriction, slidably mounted upstream of said stationary perforated plate within said recess between said annular constriction and said stationary plate with its peripheral edge facing said first shoulder and means for clamping said annular body between said opposed pipe flanges and said radially projecting portion of said stationary perforated plate against said second shoulder, and control means mounted on said annular body for moving said mobile plate transversely to the axis of said annular body to vary the perforations of one plate with respect to the other, and wherein said annular recess radially projecting portion on the downstream side of said annular body and forming said second radial shoulder is of a radial depth in excess of the diameter of said radially projecting portion of said stationary perforated plate to define an annular seal ring recess between an opposed pipe flange and said single piece annular body, and an annular seal ring within said annular seal ring recess.