Techincal Research

With my initial thoughts being that all covers that you see on the floor are manhole covers (sewage orientated) I have now discovered that the different shapes and sizes provide completely different uses. This post is a summary of each type, explaining the functional forms of each, also briefly mentioning the materials used to make each one, I will go out and start taking photos and see if I can define which is which using this research.

Coal Hole
A coal hole is a hatch in the pavement above an underground coal bunker. They are sometimes found outside houses that existed during the period when coal was widely used for domestic heating from the early 19th century to the middle 20th century. In Britain they became largely redundant within the major cities of the UK when the Clean Air Act forced a move towards oil and gas for home heating.

The hatch is typically about 12 to 14 inches (30 to 35 cm) in diameter and consists of a cast iron ring set into the pavement, with a circular cover, often made of cast iron alone but sometimes containing concrete or glass panes or small ventilation holes. There are three main reasons for the circular shape of the coal hole plate: a circular disc can not accidentally fall through its own hole (unlike a square or rectangular one); its weight means that it can be rolled rather than carried or lifted; and the absence of corners allows for a reduced risk of damage to it.

Storm Drain (Grated Inlet)
There are two main types of storm-water drain (storm sewer) inlets; side inlets and grated inlets. Side inlets are located adjacent to the curb (kerb) and rely on the ability of the opening under the backstone or lintel to capture flow. They are usually depressed at the invert of the channel to improve capture capacity.Grated inlets have gratings or grids to prevent large objects and debris from falling into the sewer system. However, their bars are fairly widely spaced so that the flow of water is not impeded. Consequently, many small objects can fall through.

Manhole Cover
A manhole cover is a removable plate forming the lid over the opening of a manhole, to prevent anyone from falling in and to keep unauthorized persons out.

Manhole covers usually weigh more than 50 kg, partly because the weight keeps them in place when traffic passes over them, and partly because they are often made out of cast iron, sometimes with in fills of concrete. This makes them inexpensive, strong, and heavy. A manhole cover sits on metal base, with a smaller inset rim which fits the cover. The base and cover are sometimes called "castings," because they are made by a casting process.