In the installation of a sewer system, it is necessary to lay the successive lengths of pipe in exact alignment with one another. When it is necessary to change the pipe to another direction, as would be true at a street intersection or at a bending in the street, a manhole is installed to allow the necessary change in direction. Not only does the manhole serve as a junction-piece, but it serves as an access means to permit clearing of the lengths of pipe by "rodding". The manhole is a fairly large concrete tubular element which is set vertically and which is provided with pipe holes adjacent its lower end adapted to receive the ends of the pipe. The sewage flows from an inlet pipe along an open groove (called an "invert") and flows into an exit pipe. In this way, a sewer maintenance man may climb down into the manhole and introduce a cleaning rod into either the inlet or the outlet pipe for the purpose of clearing accumulations or blockage. In the past, a manhole has been supplied to the contractor who is installing the sewer system in the form of a concrete tube having open lower end which during installation rests on the bottom of the trench. It has then been necessary for a worker to climb into the manhole and to build up a floor on the bottom of the manhole of brick and concrete. The floor is built up high enough to form the invert and also to provided sloping floor surfaces sloping down into the invert. This is a time consuming and labor-entensive operation. Furthermore, the resulting floor (particularly because of presence of the brick) tends to have an awkward appearance and there is a tendency for sewerage to catch loose or mislocated brick causing a blockage. Furthermore, because the operation takes such a long time, it is a time-limiting factor in the sewage installation project and, therefore, makes the project more expensive. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
An outstanding object of the present invention is the provision of a sewer form which permits the formation in the field of a floor and invert in a manhole by pouring concrete. A further object of the present invention is the provision of a sewer form for forming an invert having any of the conventional number and direction of inlet and outlet branches.
It is another object of the instant invention to provide a sewer form which is simple in construction, which is inexpensive to manufacture, and which is capable of a long life of useful services with a minimum of maintenance.
A still further object of the invention is the provision of a sewer form which is light in weight and is easily carried from one place to another, as well as easily removed from the manhole after use.
It is a further object of the invention to provide a sewer form for forming an invert in a manhole, which form permits the invert to be constructed by unskilled labor.
It is a still further object of the present invention to provide a sewer from which permits a floor and invert to be constructed that is perfect in appearance and which is smooth enough to allow sewerage to flow unobstructedly through perfectly-formed inverts.