Waste water pumps transport heavily contaminated water which often contains solid particles of various organic, inorganic and mineral origin. Single-stage designs are preferable. Waste water pumps are generally not self-priming. They are completely submerged in the fluid handled. Wear-resistant mechanical seals are used as a shaft seal. Typical applications are those of the food processing, construction, pulp and paper, sugar, and metal industries (e. g. metal electrolysis) as well as mining and water extraction (e. g. cooling water, seawater desalination). A distinction is made between municipal and industrial waste water pumps as the requirements differ considerably. Municipal waste water pumps, also referred to as sewage pumps, typically transport the following fluids: raw sewage , mechanically treated waste water from treatment tanks, sludge (e. g. activated, raw, digested and return activated sludge) as well as stormwater. For industrial waste water pumps the selection of suitable materials is crucial as industrial waste water can be highly aggressive or abrasive. The pump casing can be especially fitted with casing wear rings or wear plates which are made of particularly wear-resistant materials and can be easily replaced. Waste water pumps can be designed for either wet well or dry installation. Waste water pumps for wet well installation are also referred to as submersible motor pumps. Metering pump (Chemical dosing pump) Most metering pumps are oscillating displacement pumps. An exactly defined volume of liquid is drawn into the displacement body on the reciprocal stroke and forced into the metering line on the compression stroke. The pump settings can be changed to achieve consistently accurate metering.