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Umbrella Washers, which are also called Sela Washers, are similar to Bonding Washers with a slight twist. Comparing to the Bonding Washer, Umbrella Washers is the combination of a large umbrella shaped EPDM and flat washer. The purpose of the Umbrella washer is to be fastened on the roof with wave shaped sheets.
The EPDM Washer on the Umbrella Washer is a low-cost weather resistant rubber and can withstand up to 275°F. Although EPDM rubbers are the most common, there are other types of rubber also made for similar purposes, such as neoprene and silicone. The Umbrella Washers are best to be fastened on the top of the wave curvature. The large EPDM under the Umbrella Washer can provide the similar sealing effect of the Bonding Washer in this area. The Flat Washer on the top of the umbrella EPDM washer will provide a distributed force to expand the EPDM washer inward and outward.
The installation for screws with Umbrella Washer is not as easy as it seems. The incorrect installations of the screw will give insufficient or excessive tightening to the Umbrella Washer. This may cause water leakage around the EPDM or damage to the EPDM and create gaps between the objects. The correct installation should push the EPDM outward and inward to fully cover the surface of the Flat Washer and the screw threads on the inside. Most Umbrella Washers are made with zinc coatings to prevent corrosion.
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