Series GYW flow indicators utilize a double-wall construction and are used on flanged piping systems handling highly corrosive and ultra-pure liquids compatible with Pyrex glass. They cannot be used with hydrofluoric acid or sodium hydroxide as they will etch the Pyrex cylinder wall. Natural polypropylene ends are standard and are also the least expensive. FKM seals are standard. These indicators will fit 1-1/2" smooth face standard companion flanges as well as DIN (European standard) flanges. Two flange O-ring seals are supplied; therefore, other gasket materials are not required. An optional fluttering device is also offered. Flow indicators are designed to indicate the presence or clarity of high purity or corrosive liquid in a piping system. For use with ultrapure liquids or chemicals compatible with acrylic. O-ring seals are used on indicators allowing them to seal at extremely low pressures as well as high pressures. Flow indicators are full ported, eliminating any possible flow resistance. Standard O-ring seals are Viton. Standard fasteners are stainless steel. The transparent outer cylinder wall is high impact strength acrylic. The inner wall (wetted) is Pyrex. Made of PVC.