How to Select Chemical Pumps

Image Credit: All-Flo Pump Company, LLC. | Gorman-Rupp Industries | Clark Solutions

Chemical pumps are pumps designed to move chemicals or chemical slurries. They are designed and constructed to handle substances with varying levels of viscosity, corrosiveness, and abrasiveness. Some of these pumps are also metering pumps, which provide flow measurement and control for applications which require precise volumes of chemicals.

Operation

Chemical 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 chemical pump requires an analysis of different pump types.

Among dynamic pumps, types include centrifugal and special effect pumps.

• Centrifugal pumps are typically characterized by high flow rates and low to medium head. They are best at handling low viscosity chemicals. Subtypes of centrifugal pumps are axial, mixed, and radial flow pumps.
  • Axial flow pumps provide the highest flow rates and lowest head of centrifugal pumps
  • Mixed flow pumps are designed to incorporate characteristics of axial and radial flow, providing medium flow rates and head.
  • Radial flow pumps provide the highest flow head and lowest flow rates of centrifugal pumps
• Special effect pumps include specially propelled or powered pumps such as hydraulic, gas lift, and electromagnetic pumps. They provide specific advantages for specialized applications. For example, electromagnetic pumps do not have a mechanical seal, making the pump leak free and low-maintenance which is important for toxic or corrosive chemicals.

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 chemicals. 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 chemicals.
  Peristaltic pumps require no seal and have no leakage, making them a good choice for handling disinfectants, corrosives, and chemicals containing solids.
  • Rotary vane pumps are able to handle thick and thin liquids well, making them ideal for applications handling multiple clean chemicals 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 chemicals. Subtypes include diaphragm, piston, and plunger pumps.
  • Diaphragm pumps are seal-less pumps which can run dry and can handle a wide range of liquids, including chemicals containing solids and corrosives.
  • 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.

For more information on the operating and performance characteristics of these pump types, visit the Industrial Liquid Handling Pumps page on GlobalSpec.

Specifications

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

• Flowrate describes the rate of volume discharge through the pump, given in gallons per minute (gpm) or gallons per hour (gph) for low-flow or metering 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.
• Horsepower indicates the output power of the pump, measured in units of horsepower (hp).

Selection tip: Selections above 70 hp should be reviewed carefully from a bearing and mechanical seal reliability standpoint before making a purchase.

• 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 chemical 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 and thermoplastics may be the least expensive base materials, and provide excellent corrosion resistance from acids and various chemicals.
• Stainless steel alloys provide protection against chemical and rust corrosion, and have higher pressure ratings than most plastics.
• Cast iron provides excellent strength and abrasion resistance, with high pressure ratings. 

References

Grainger - Chemical Pumps

• Diaphragm Pumps Enhance Chemical Injection Systems During EOR
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• When to Use PD Pumps (Copyright Viking Pump, Inc.)
  pump's flow rate and efficiency. PD pumps maintain. their flow rate and efficiency even with significant changes in pressure. Variations in. Many liquids vary in viscosity depending on temperature or due to. Viscosity. chemical reaction. A rise in viscosity will independently alter the flow. rate...
• Sizing and Selecting Metering Pumps Planning a Metering Pump Installation (.pdf)
  abrasive slurries. Is the chemical viscous or is the chemical a slurry? Does the chemical release. gas? Special liquid ends are available for these specific applications. Standard metering. pumps handle clear liquids with viscosities ranging from water-like to 1500 cps. Special. liquid ends can...