A drop shaft is used to connect a shallow storm or sanitary sewer with a deeper pipe or interceptor tunnel. The flow may either drop freely within the shaft or be piped downward. Sometimes a spiral technique is used to decrease the velocity of the flow. These shafts need to also be maintained properly based on the internal structure and how they have deteriorated.
Valve, Diversion, and Overflow Structures
Valve chambers shut off the flow to a pipe or divert it into a parallel line. These are most frequently used on a pressure pipe system. Overflow structures are susceptible to corrosion and deteriorate faster than the rest of the system. There are few standard shaped parts in these systems and this creates difficulty in maintenance and repair, and because the sewer lines tend to be very deep, the groundwater pressure in the actual groundwater is high and puts considerable stress on the pipes allowing for inflow, causing greater problems with volume at the sewage treatment plant.