Dwyer, 451-AF, Series 250-AF Inclined Manometer Air Filter Gage, 0-1' w.c., 8' Inclined ScalePrecision Machined, Solid Acrylic Plastic Gages, Accurate To ±1% Of Full ScaleDwyer® Durablock® Series 250-AF Gagesare precision machined 1" thick solid acrylic plastic, virtually unbreakable and free of distortion. The fluid bore is precision drilled to ±.0002" to assure life long accuracy. A glass spirit level is built into the body and encapsulated to prevent damage or tampering. The scale is mirror polished chrome plated brass to assure parallax free reading by alignment of the meniscus with its reflection. Safety traps are incorporated in the body to prevent loss of fluid due to pressure surges. Red and green signal flags indicate clearly when a filter change is necessary. Gages are suitable for use in ambient temperatures of -20 to 150°F. Connection fittings are positively sealed by"O" rings but easily removed for zeroing or addition of fluid. Furnished complete with instructions.Economy Models 451-AF and 452-AF are similar to 250 Series except they are not equipped with over pressure traps. Two A-324 1/4" compression fittings are included with each Gage. Bodies are of 5/8" thick acrylic and scales are mirror polished, epoxy coated aluminum.FeaturesHighly accurate and easy to use yet almost indestructible, Dwyer® Series 250-AF Inclined Air Filter Gages are foolproof and dependable. There are no moving parts - no mechanical linkages - nothing to wear out, jam or deteriorate from vibration. They never need calibration. The mirror polished inclined scale allows the operator to easily read minute differences in differential pressure across the filter accurately without parallax error.The only servicing required is occasional zeroing. If cleaning is necessary, it is easily done with soap and water.