Suitable for applications such as crude oil, where a 16″ or 20″ full opening and 8″ fill opening is needed. Recommended working pressure is 25 PSI. “Ball in Socket” hinge and cam design provides positive locking and prevents 8″ cover from fully opening when trailer is still under pressure. Cover assembly is available in Mild Steel Plated. Buna N base gasket and bolts and nuts are optional and available.