Two butterfly valves can share the same size, the same PN16 rating and the same EPDM liner \u2014 and still be completely different valves, because of how the body meets the pipe. Wafer, semi-lugged, fully lugged and flanged bodies behave differently during maintenance, in dead-end service and at large diameters. Specify the wrong one and the problem only shows up the day someone needs to remove the downstream pipework.<\/p>\n
A wafer valve has no bolt holes of its own. It is sandwiched between two pipe flanges, and the flange bolts pass straight through from one flange to the other, clamping the valve between them. That makes it the lightest, most compact and most economical body type \u2014 which is why it is the default choice for HVAC and treated-water lines.<\/p>\n
The limitation is structural: the valve is only held in place by the compression of both<\/em> flanges. If the downstream pipe is unbolted, nothing retains the valve or holds pressure. A wafer valve therefore cannot be used for dead-end service or as the last valve before removable equipment.<\/p>\n In the Niagara butterfly valve range<\/a>, the FFS80W and FFS80GW are wafer-type ductile iron valves, WRAS approved for potable water up to 80 \u00b0C, rated PN16 and hydrostatically tested to 24 bar (shell) and 17.6 bar (seat) \u2014 covering DN50\u2013DN200 (Fig. 970W) and up to DN600 (Fig. 970WG).<\/p>\n A semi-lugged body adds locating lugs around the periphery. Its practical advantage is alignment and cross-standard fit: the same valve body accepts PN10, PN16 or ANSI Class 125 flange drillings \u2014 useful on sites where European and American pipework meet.<\/p>\n Niagara’s FS50 and FS50G are semi-lugged valves in epoxy-coated ductile iron with anti-blowout stems, covering DN50\u2013DN200 and DN50\u2013DN300 respectively. The FS50W\/FS50GW variants carry WRAS approval for potable water and extend to DN600, and the FSDG50\/FSDG50G add gearbox operation. Like wafer bodies, semi-lugged valves still rely on both flanges being in place \u2014 they do not provide dead-end capability.<\/p>\n A fully lugged valve has threaded lugs, so each flange bolts to the valve independently. The downstream pipe can be unbolted and removed while the valve stays anchored to the upstream flange \u2014 this is the body type to specify at pump connections, strainer positions and anywhere equipment will be removed for service. Whether a specific model may hold pressure in true dead-end service, and at what rating, must be confirmed against its datasheet.<\/p>\n This is the deepest part of the Niagara range:<\/p>\n A flanged (double-flanged) valve has its own integral flanges, bolted to the pipe flanges like any other flanged fitting. It is the heaviest and most expensive body \u2014 and the standard choice for large diameters, buried service and pumping stations, where the rigidity of an integral flange matters more than weight.<\/p>\n Niagara’s FFB20\/FFB21, FFSD30\/FFSD31 and FFS40\/FFS41 are flanged valves to BS EN 593 for PN16 flanges, DN50\u2013DN200, with ductile iron, stainless steel or aluminium bronze disc options and EPDM or Nitrile liners. At the top of the range, the FFS1150G series covers 26″ to 56″ in ANSI Class 150 with ASME B16.47A end connections \u2014 municipal transmission territory. The FB20\/FSD30\/FS40 series offers a universal pattern fitting both PN16 and Class 125 drillings.<\/p>\nSemi-lugged: flexibility across flange standards<\/h2>\n
Fully lugged: built for maintenance and dead-end duty<\/h2>\n
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Flanged: the large-diameter workhorse<\/h2>\n
Comparison at a glance<\/h2>\n