A manhole cover is a sealing device used on ships to close manholes. Based on the installation method, it is divided into protruding and embedded types. The material is mostly hot-rolled carbon steel or the same steel as the hull, while the bolts and nuts are made of stainless steel or galvanized carbon steel.
The international standard ISO 5894:2018, revised under my country's leadership, added the embedded manhole cover type and stipulated that asbestos-free materials are required.
Protruding manhole covers include three types: A, B, and C. Type A has a 100mm high coaming and is suitable for compartments prone to water accumulation; Type B has an elongated oval structure for deck platforms; and Type C is suitable for container areas. Embedded types D and E are installed on the bottom of cargo holds and other areas requiring a flat surface.
Watertight compartments use water-resistant rubber gaskets, oil tanks are equipped with oil-resistant seals, and jet fuel tank covers are made of brass. During installation, they must be staggered from the lower deck, with the long axis of the through-hole set vertically, and the lower edge at least 500mm above the bottom plate.
The protective device patent achieves stable support through a primary and secondary support leg structure, while the balancer patent utilizes a cylinder to reduce operational difficulty. Some models are equipped with a breathing valve to balance the internal and external pressure difference, and the emergency exhaust volume exceeds 7000 m³/h.
