Introductin of Precast Concrete Manhole
The precast concrete manhole is widely used for its high density and strength, antiknock characteristic and impermeability are much much better than the concrete block manhole.
A manhole system consists of: the manhole cover, manhole base, manhole ring, and manhole top. The manhole body is ordinary circular, but it could be made to rectangular, flabellate, and in other irregular shapes too. The height of manhole could be adjusted by manhole rings to meet requests of different projects.
1. Manhole Top
There are different kinds of manhole tops such as: cylinder-shaped, cone-shaped, and horseshoe-shaped. When the manhole rings are normal size like 700mm, 800mm, cylinder-shaped top is commonly used. When the manhole rings are 1000mm, 1200mm, 1500mm, the cone-shaped top is an option. When ladders are necessary for people to go inside of the manhole, the horseshoe-shaped manhole is considered the better option.
2. Manhole Ring
There are manhole rings connecting the manhole top and basement, and manhole rings are used to adjust the depth of manhole too.
3. Manhole Base
Manhole base is the functional parts of the manhole system, and its dimension affects the function of the manhole system.
Ordinary there are to shapes of manhole base, circular and rectangular. Circular manhole base is easier to produce, and pipes can be inlet in 360°, but it takes more maximum plane size. Rectangular manhole base is commonly used in large pipelines and right-angled pipelines.
The distance between top of manhole base and the edge of inlet pipes should more than 150mm, the distance between the base bottom and the edge of inlet pipes should more than 50mm, and the distance between pipes should more than 100mm when there are several inlet pipes needed.
Concrete manhole with base: the base is precasted together with manhole body, reduced the lifting work during installation, but not very convenient to install.
Manhole without base: the manhole bottom base and manhole are cast separately, and installed together,
The most inconvenience during the project is that the manhole is difficult to lift and install. So the design of the manhole item should be focused on reducing the weight, the assembly of manhole system could be adjusted according to different project, larger manhole base could be made in half and half to make it easier to lift and install, and to meet the different requirement in different geographic places.
The inlet for pipes in the manhole base can be circular shaped, U shaped, and blind pit. The blind pit is kind of reserved hole, only half depth of the inlet, need to open when needed.
The gutter is ordinarily designed in the manhole for the request of current fluency. The gutter can be cast together with manhole base or cast separately, and assembled together when necessary.
The manhole as a trance to the underground pipeline, installation of ladders are necessary, and the ladders should be safe, durable. There are steel ladder and steel reinforced plastic ladder, the steel ladder goes rust easily and is replaced by the other one gradually.
5. Joints of Concrete Manhole
Joints between the manhole elements are almost the same with concrete pipes, there are flat joints, as well as male & female joints. The seals for the gap are cement plaster, factice, and rubber seal.
Concrete Manhole Manufacturing
Wet Cast Manhole Mold
Wet cast manhole mold uses the steel mold to manufacturing precast manholes, using wet concrete as aggregate, the finished manhole will cure inside the mold until it becomes solid to remove the mold. This mold is suitable for Low-Rate Initial Production.
Automatic Concrete Manhole Machine
Concrete manhole machine uses dry concrete as aggregate, and with the high-frequency vibration force, the finished manhole product has high density and strength, the mold could be removed instantly after production. This machine is suitable for mass production.