This case study appeared in WWD December 2020 issue.
Sewer drops have traditionally been constructed outside of the manhole, a technique that has proven troublesome over time. Outside drops are expensive to construct, requiring excavation down to the manhole invert elevation. Outside drops are difficult to access for inspection and cleaning, leaving them prone to clogging and failure. A failed outside drop can lead to infiltration into the manhole.
The RELINER/Duran Inc. Inside Drop System is designed to address these issues and control flow using simple, cost effective components inside the manhole for easy installation. The system consists of a marine grade fiberglass drop bowl that is bolted to the manhole wall just beneath the high-level inflow pipe. Stainless steel pipe support brackets are used to attach the drop pipe to the manhole wall. The drop bowl does not touch the incoming pipe and protrudes minimally into the structure. The resulting drop pipe is just off the manhole wall and securely fastened. A flexible coupler is used to connect the drop pipe to the drop bowl, and a bend is installed at the pipe base in the manhole invert. An optional force line hood is available for high velocity applications.
The system is easy to install and allows the drop to be cleaned and inspected from above. The system can be used for main line, service connection, and wet well drops. These products are made in the USA and accommodate internal drops ranging from 4 inches to 24 inches in diameter in a variety of different structure sizes.