De Dietrich 97570027 flange sight hole

A flange sight hole is a fitting mounted on the boiler casing or burner front plate to allow visual inspection of the flame during operation or commissioning. Parts of this type consist of a flanged body, a glass window, and a sealing gasket. They provide a direct view of the combustion chamber without opening the appliance, enabling the engineer to check flame shape, colour, and stability, and to verify electrode position or burner head condition. Such sight holes are typically installed on the access door or on a dedicated flange connection. The glass must withstand the operating temperature of the combustion chamber and the pressure inside the boiler. When replacing a sight hole, the key selection parameters are the flange outer diameter, the bolt hole pattern and number, the gasket type (flat fibre, graphite, or silicone), and the glass material (borosilicate or quartz for higher temperature ratings). The unit is sealed against flue gas leakage, so the gasket must be undamaged and the glass free of cracks. The article listed under De Dietrich 97570027 and 336.889.002 is a flange sight hole from that manufacturer. It belongs to the category of boiler pipes, flanges and connections. As with any manufacturer-specific connection component, the geometry and bolt pattern are fixed to the appliance model; a generic replacement may not match the flange dimensions or the sealing surface.