How to Select Dosing Pumps

Image Credit: Mahr Metering Systems Corporation | Waston Marlow Pumps Group

Dosing pumps are low-volume pumps with controllable discharge rates that are used to inject additives or difficult-to-mix fluids into mixing, pumping, or batch/tank systems. Dosing pumps are usually made from plastic, thermoplastic, or stainless steel and feature mounting holes or accessories. Dosing pumps often have a controller which enables the fluid flow to be monitored and adjusted easily.

Operation

Dosing pumps can be designed to operate based on a dynamic or positive displacement principle. Dynamic pumps, and their subtype centrifugal pumps, utilize fluid momentum and velocity to generate pump pressure while positive displacement pumps use expanding and contracting cavities to move fluids. Dynamic pumps produce a variable flow suited for generating high flow rates with low viscosity fluids, while positive displacement pumps produce a constant flow suited for producing high pressures (and low flow rates) with high viscosity fluids.

Pump Types

Selecting a suitable dosing pump requires an analysis of different pump types. Most dosing pumps are positive displacement pumps, which provide steady, low flow for a variety of types of media.

Among positive displacement pumps, types include rotary and reciprocating pumps.

• Rotary pumps are typically characterized by medium flow rates and low to medium head. They provide a smooth flow and are best suited for clean, non-abrasive, viscous fluids. Subtypes of rotary pumps include screw, peristaltic, gear, and rotary vane pumps.
  • Gear pumps contain few moving parts and are the ideal choice for clean oils and other clean, high viscosity liquids.
  Peristaltic pumpsrequire no seal and have no leakage, making them a good choice for handling disinfectants, corrosives, and slurries.
  • Rotary vane pumps are able to handle thick and thin liquids well, making them ideal for applications handling multiple clean liquids of varying viscosities.
  • Screw pumps provide the highest flow rates of positive displacement pumps. They can handle oils, fuels, and other high viscosity liquids.
• Reciprocating pumps are typically characterized by low flow rates and high head. They provide a pulsed flow able to handle dirty, tacky, and viscous liquids. Subtypes include diaphragm, piston, and plunger pumps.
  • Diaphragm pumps are seal-less pumps which can run dry and can handle a wide range of fluids, including liquids which contain solids and corrosives. These are among the most common types of dosing pumps.
  • Piston pumps can provide very high pressure and are best suited for high head applications involving abrasive liquids.
  • Plunger pumps provide the best means to achieve very high pressures. They are best suited for water and other thin liquids. 

Specifications

The primary specifications to consider when selecting dosing pumps are accuracy, flowrate, pump head, pressure, horsepower, power rating, outlet diameter, and operating temperature.

• Accuracy describes how close a volume of pumped fluid is to the exact desired value. Pumps with higher accuracy will pump measured volumes of fluid with more precision and repeatability. Accuracy is given in a +/- value or % variability.
• Flowrate describes the rate of volume discharge through the pump, usually given in gallons per hour (gph) for low-flow dosing applications.
• Head defines the energy supplied to liquid (per unit weight) by the pump. It is expressed as a column height of liquid (either vertical lift or suction), given in feet of head (ft).
• Pressure describes the operational pressure of the pump. It is usually given in pounds per square inch (psi) or bar. In the case of dosing pumps, it describes the maximum pressure or pressure range that the pump is guaranteed to pump against at a relatively controllable flow rate.
• Horsepower indicates the output power of the pump, measured in units of horsepower (hp).
• Power rating indicates the power required to operate the pump, measured in Watts (W) or horsepower (hp). In the case of electric pumps, some manufacturers will instead specify the required voltage (in volts or V) and current (in amps or A). The power rating is the product of the voltage and current ratings (power = voltage x current).
• Outlet diameter is the size of the discharge or outlet connection of the pump. Inner diameter (I.D.) describes the size of the inner opening while outer diameter (O.D.) specifies the entire opening size including the pipe thickness.
• Operating temperature defines the range of temperatures or temperature limit of the media handled by the pump.

For a more in depth understanding of pump specifications, performance curves, and operation, visit the Industrial Liquid Handling Pumps information page on GlobalSpec.

Materials

The base material of a dosing pump is important to consider, as it affects the type of media that can be handled effectively. System fluids may be abrasive, acidic, caustic, tacky, very hot, very cold, or otherwise hazardous. Base materials such as cast iron, plastic, and stainless steel possess different advantages for handling these various characteristics.

• Plastics are the least expensive base materials, and provide excellent corrosion resistance and protection from a broad range of chemicals.
• Stainless steel alloys provide excellent protection against various chemicals and rust corrosion, and have higher pressure ratings than most plastics.
• Cast iron provides excellent strength and abrasion resistance, with high pressure ratings.

Applications

Dosing pumps are used in a variety of commercial, industrial, municipal, and maritime applications. Examples include agriculture and horticulture, dairy farms, breweries and distilleries, construction, food service and food processing, power generation, and oil and gas production. Dosing pumps are also used in the aerospace and defense, automotive, machine tool, mining, medical, pharmaceutical, semiconductor, and paper industries. Cryogenic pumps are rated for conditions where temperatures are low enough for gases to condense to become liquids or solids.

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