20230918 20200300 1.0 TRUE Pressurized Main The feature is a line shapefile that has three subtypes to classify data; force, low-pressure, and vacuum. Force mains are pipelines that convey wastewater under pressure from the discharge side of a pump or pneumatic ejector to a discharge point. Pumps or compressors located in a lift station provide the energy for wastewater conveyance in force mains. A low pressure main uses a small pump stations to move wastewater through the transmission system. A vacuum evacuates air from a closed volume and develops a pressure differential between the volume and the surrounding atmosphere. Baltimore County, Maryland Department of Public Works