The difference lies in how it is fitted to the pipework. A wafer-type butterfly valve is clamped directly between two mating flanges on the pipework without its own flanges and held in place by through bolts – it is compact, lightweight and cost-effective. A flanged butterfly valve (lug design) has its own integral threaded holes at the ends and can be bolted to a flange on one side using stud bolts, allowing for a detachable connection on each side. The lug design is therefore particularly suitable for dead-end service – i.e. wherever one side of the pipeline needs to be isolated from pressure without dismantling the opposite side. Both designs are available from stock at FERGO as part of the Fergo butterfly valve range.