Dry Pit Definition

What is a Dry Pit?

A dry pit is a below-grade structure located adjacent to a below-grade sump for holding a liquid such as wastewater. The dry pit is the mechanical room where pumps are installed to pump the liquid out of the adjacent sump.

The most common modern municipal wastewater pump station design utilizes submersible pumps which are submerged directly into the wastewater they are pumping. However, an alternative design, and one that was popular in the past, is the wet-pit/dry-pit configuration.

In the wet-pit/dry-pit configuration it is common to use pumps that were not designed for submerged operation. The wet-pit is a below-grade sump in which wastewater is collected. The dry-pit is located adjacent to the wet-pit and is where pumps are installed. The pumps in the dry-pit take suction from the wet-pit by way of piping which penetrates from the dry-pit into the wet-pit.

The pumps installed into a dry pit are called dry pit pumps, solids-handling pumps, or non-clogs. Alternatively, submersible pumps may also be installed into a dry pit as long as some type of cooling water is circulated around the submersible motors which depend on external liquid for cooling.