This article takes an in-depth look at metering pumps and their use.
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A metering pump is a specialized mechanism designed to precisely dispense a predetermined volume of fluid at a desired rate, ensuring controlled volumetric flow. The phrase "metering pump" encompasses a range of pumping technologies, each engineered to fulfill unique application, operational, or process demands. The specific selection of a metering pump is determined by the requirements of the particular application.
In choosing a metering pump, it is crucial to consider factors such as the fluid's viscosity, temperature, discharge pressure, flow rate, and the composition of materials in the wetted path. A metering pump typically consists of a pump head and a motor, which can feature either manual or electronic control systems for adjustments.
Metering pumps often employ piston-driven positive displacement techniques, where the piston transfers the liquid within the reservoir chamber. Although piston-driven pumps are widely used, alternative designs exist to meet specialized requirements.
A metering pump is a type of reciprocating pump that uses positive displacement to deliver a precise, controlled volume of liquid with each stroke. These pumps are essential in dosing, blending, and injecting fluids in a wide range of industrial, municipal, and laboratory applications. Their rotary motion is translated into reciprocating movement via a wheel and worm shaft mechanism, although specific configurations may vary between different metering pump designs. Metering pumps are valued for their accuracy and repeatability, offering exceptional control over the dosage and flow rate of various chemical or process fluids.
The primary function of a metering pump is to ensure that the correct volume of liquid is transferred during a process, whether it’s water treatment, chemical dosing, pharmaceutical formulation, or food and beverage processing. By ensuring precise dosing, metering pumps help operators achieve consistent product quality, regulatory compliance, and process efficiency.
There are several types of metering pumps, each engineered for specific applications across industries like water treatment, chemical injection, oil and gas, food and beverage, and pharmaceuticals. The choice of metering pump often depends on the liquid’s viscosity, corrosiveness, required flow rate, pressure, and automation needs. Understanding these differences is key when selecting the optimal dosing pump for your system.
Piston metering pumps are a reliable positive displacement pump design that utilizes a reciprocating piston to move fluids within the chamber. The flow rate and volume of liquid dispensed are governed by the diameter and stroke length of the pumping chamber. Fluid flows through check valves—located at both the inlet and outlet—ensuring directional flow and effective discharge.
As the piston retracts, a vacuum is created in the chamber, opening the inlet check valve and drawing the fluid into the chamber. During the discharge stroke, the piston pushes the liquid through the outlet valve. Piston metering pumps excel at handling high-pressure duties and chemically compatible fluids—ideal for precise dosing in laboratory, industrial, and petrochemical applications.
A diaphragm metering pump employs a flexible diaphragm to draw liquid into the pumping chamber and then expel it. This positive displacement pump is popular thanks to its leak-free operation, making it suitable for transferring corrosive, hazardous, or abrasive chemicals. The diaphragms can be operated mechanically or hydraulically. In mechanical diaphragm pumps, the diaphragm is directly coupled to a plunger or lever arm; in hydraulic diaphragm pumps, hydraulic fluid acts as an intermediary to move the diaphragm.
The diaphragm movement generates suction, pulling fluid through the inlet valve and then forcing it out through the outlet valve, ensuring consistent volumetric accuracy. Diaphragm metering pumps are commonly used in water treatment, agriculture, industrial processing, and chemical dosing where accuracy and chemical compatibility are critical.
Peristaltic metering pumps, also known as tube or hose pumps, operate differently from piston and diaphragm pumps. They use a flexible tube or hose, which is compressed and released by rotating rollers or shoes on a spinning rotor. This creates a vacuum that draws fluid into the hose and propels it forward by peristaltic action. The process offers exceptionally gentle handling of shear-sensitive fluids and provides consistent flow even with slurries or viscous media.
Peristaltic metering pumps are ideal for applications involving aggressive, abrasive, or particulate-laden liquids, as the pumped fluid only contacts the inside of the tube, reducing contamination and wear. These dosing pumps are used extensively in pharmaceuticals, food and beverage, laboratory automation, and chemical processing.
A gear metering pump is a rotary positive displacement pump that features intermeshing gears to create a vacuum and draw fluid into the chamber. As gears rotate, they trap and convey the fluid between gear teeth from the inlet side to the discharge port, producing a steady, pulseless flow.
Well-suited to high-viscosity fluids and high-pressure processes, gear metering pumps are utilized in hydraulic systems, lubrication, polymer delivery, chemical dosing, and fuel injection. Their ability to precisely meter thick, viscous, or lubricating fluids makes them a preferred option in oil and gas, chemicals, and manufacturing industries.
Syringe metering pumps are precision instruments designed for laboratory, medical, and research applications where ultra-precise dosing or sampling is essential. Infusion syringe metering pumps deliver minute quantities of liquids at tightly controlled pressures and intervals—vital for drug delivery, chromatography, and titration. Withdrawal syringe metering pumps, on the other hand, are engineered to automatically extract and transfer fluid samples for analysis or testing.
Syringe pumps are prized for their exceptional accuracy in micro- and nano-liter dosing. Their slower metering rates and low-volume reservoirs make them ideal for specialized applications, such as laboratory analysis, medical dosing, or calibration, rather than bulk fluid transfer. Multiple syringe pumps can also be utilized for simultaneous delivery of different reagents or test fluids.
Bellows metering pumps utilize an elastic bellows structure that expands and contracts to displace fluid. The up-and-down motion, typically generated by a motor-driven lever, enables the pump to draw fluid in through an inlet valve during expansion and expel it through an outlet valve during contraction. This simple yet effective mechanism is ideal for the precise dosing of low- to medium-viscosity fluids.
Commonly used in medical devices, instrumentation, inkjet printing, and analytical equipment, bellows metering pumps are valued for their reliability, chemical resistance, and ability to handle small flow rates with minimal pulsation or contamination.
Plunger metering pumps work similarly to piston pumps but use a robust plunger instead of a piston, often enabling them to achieve ultra-high discharge pressures—sometimes exceeding 50,000 psi. They are typically single-acting, drawing fluid through a suction check valve and then forcibly expelling it through a discharge valve during the plunger’s forward stroke.
Plunger pumps are ideal for high-pressure applications in oil and gas, process engineering, and industrial cleaning. They excel in applications where reliability under extreme pressures is vital, but are less suitable for fluids with abrasive solids, as the plunger design is subject to direct wear.
Small metering pumps—often called micro or mini metering pumps—are compact solutions for precise fluid transfer in confined spaces or portable systems. They feature a minimized pump head, efficient micro-motor, and scaled-down driver components. Despite their size, these pumps offer accurate dosing and adaptability across diverse liquid media, making them common in dosing, sampling, laboratory, instrumentation, and OEM equipment integration.
Modular design allows small metering pumps to be customized for specific applications, including adjustment of stroke frequency, flow rate, and discharge volume. When used in parallel, several small metering pumps can simultaneously handle multiple fluid streams within a single automated or batch processing system.
Their light weight and versatility make them easy to configure and install—frequently used in water treatment, medical dosing, and process automation where space and reliability are essential.
Chemical metering pumps are engineered for high-accuracy dosing of chemicals, additives, or reagents in demanding industrial and municipal processes. Precision and repeatability are critical, as over- or under-dosing chemicals can impact product quality, safety, or regulatory compliance. These dosing pumps are built with chemically resistant materials—such as PTFE, PVDF, or stainless steel—to handle aggressive, hazardous, or corrosive fluids.
Common dosing applications include controlling water pH, disinfection, scale inhibition, coagulation, and flocculation, as well as the addition of polymers, caustics, acids, and fuel additives. Chemical metering pumps are crucial in wastewater treatment, boiler feed, oil and gas, agriculture, and mining operations. Advanced models offer digital or automatic control, integrated sensors for feedback, and customizable flow adjustment, supporting automated chemical injection and continuous flow processes.
Examples of typical chemical metering pump applications include:
pH Control: In industrial and municipal water treatment, metering pumps accurately dispense chemicals such as sodium hypochlorite, sulfuric acid, or caustic soda to adjust water pH and ensure regulatory compliance.
Coagulation and Flocculation: For the removal of suspended solids and contaminants, pumps inject coagulants (e.g., ferric chloride) and flocculants to enhance particle aggregation and sedimentation.
Water Enhancement: Dosing pumps add disinfectants, anti-foaming agents, or nutrient additives to improve water purity and microbiological quality for drinking water or process water use.
Fuel Additives: Chemical injection pumps introduce performance-enhancing additives into fuels for combustion optimization, corrosion prevention, and storage stability.
Mining: Specialized metering pumps dispense leaching agents, pH modifiers, or flotation chemicals during ore processing for efficient mineral extraction. Each operation may require tailored dosing and flow control based on site-specific chemistry and ore characteristics.
If you need expert guidance selecting the right chemical dosing pump for your application, consider factors such as chemical compatibility, maximum discharge pressure, required flow range, available automation features, and compliance with industry standards like API 675 or NSF/ANSI 61.
Electronic metering pumps utilize electrical power (DC or AC) for energy-efficient, automated control over fluid dosing. Integrated electronics—such as microcontrollers and digital interfaces—enable operators to precisely adjust flow rates, program batch cycles, and monitor real-time pump operation. Modern EMPs often include advanced user interfaces, such as touch screens, programmable settings, and integration with SCADA or PLC systems for seamless process automation.
This high level of control makes electronic metering pumps ideal for continuous dosing, variable-speed operation, and process optimization in municipal water treatment, chemical manufacturing, pharmaceuticals, and food production. The ability to automatically adjust parameters based on feedback—such as flow sensors or pressure transmitters—supports accuracy in critical dosing applications, reducing manual intervention and error rates.
Operators can set electronic metering pumps for precise discharge rates without needing to continuously adjust for stroke length or fluctuating process conditions. Features like remote operation, data logging, and alarm outputs ensure consistent, compliant, and traceable dosing in regulated environments.
Solenoid metering pumps, also known as electromagnetic dosing pumps, use electromagnetic force to actuate their internal diaphragm. When energized, the solenoid coil retracts a plunger, flexing the diaphragm to first draw in fluid and then expel it during each reciprocating cycle. This design allows precise, pulseless fluid dosing and makes these pumps highly reliable, low-maintenance, and energy efficient.
Solenoid dosing pumps are widely used for water treatment, laboratory analysis, cooling tower chemical injection, and detergent dosing. Their straightforward setup—often including digital controls, LED indicators, and programmable flow adjustments—offers excellent user convenience and operational safety. Their ability to automatically adapt discharge volumes and stroke lengths in response to process changes ensures versatility across diverse metering pump applications.
A metering pump, also known as a dosing pump, is designed to accurately dispense various fluids, including acids, bases, corrosives, viscous liquids, and other materials, to fulfill specific process or application needs. These pumps perform repetitive dispensing tasks automatically.
The driver supplies power to the pump through various systems, including AC, DC, pneumatic, or hydraulic power sources.
The power delivered by the driver is initially in rotary motion, which must be converted into reciprocating motion for the pump mechanism to function. The drive mechanism handles this conversion, transforming the rotary motion from the driver into reciprocating movement. Under demanding conditions, this component is often submerged in a lubricant or oil bath to maintain reliability and ensure consistent performance.
Flow adjustments for a metering pump involve modifying the stroke length and the frequency of strokes per minute. These adjustments can be made manually, through axial displacement, or automatically.
Manual: Manual adjustment typically involves using a screw mechanism to turn the pump on or off.
Axial Displacement: Axial displacement can be adjusted while the pump is running, using mechanisms such as an N or L-shaped crankshaft adjustment or an eccentric cam adjustment.
Automatic: Automatic adjustments are made using pneumatic or electronic controls. Pneumatic controls alter the stroke by adjusting the air pressure signal, whereas electronic controls modify the electrical signal to adjust the stroke.
Check valves can be located at the suction end of a metering pump or at its discharge end. The designs of check valves permit the liquid flow to enter the chamber of the metering pump and allow the flow to be discharged. Aside from peristaltic pumps, most metering pumps have ball check valves with one or two balls.
Poppet check valves are frequently used in metering pumps due to their ability to ensure unidirectional flow, similar to ball check valves. The mechanism of a poppet check valve resembles that of a sink or bathtub drain plug, where a poppet opens and closes to regulate the flow of fluid.
Metering pumps are essential for various manufacturing processes, including blending, purifying, and managing fluid operations and applications. Enhancing a metering pump with the right accessories can boost its accuracy and reliability in dosing, help prevent downstream issues, and lower maintenance costs.
Each component is designed to enhance specific features of the metering pump, improving its overall performance. Chemical dosing systems often benefit from a range of accessories, such as pressure relief valves, back pressure valves, calibration cylinders, pulsation dampeners, pressure gauges, injection quills, and strainers.
When the discharge side of the pump is obstructed during operation, pressure within the pump can rise continuously, potentially leading to damage. To prevent this, a relief valve is used to release excess pressure, protecting the pump, piping, and other components from harm.
Back pressure valves are installed near the discharge side of the pump to maintain pressure on the discharge side, ensuring that the pump's internal check valves seat correctly. These valves release fluid when a predetermined pressure is achieved, thereby optimizing the pump's performance and the flow within the pipeline.
A back pressure valve functions as a control valve, maintaining pressure when the suction pressure exceeds the discharge pressure. Without it, a metering pump might experience overfeed and inaccuracies. The valve provides enough pressure to counteract the inertia of the discharged liquid, ensuring proper operation.
Injection quills are equipped with built-in check valves to prevent backflow of the dosed chemical. They are designed to introduce the chemical into the center of the flow stream, ensuring uniform distribution and thorough mixing. These quills also include flow calculations to determine the natural frequency. Beveled end injection quills enhance dispersion and reduce the risk of corrosion or fouling from concentrated chemicals.
An anti-syphon check valve combines back pressure and check valve functions to prevent siphoning, which occurs when fluid continues to flow and be drawn out after the pump stops. This issue arises when the pressure on the discharge side of the pump is lower than on the suction side. Anti-syphon check valves are designed to prevent overfeeding and backflow in the mainline, ensuring proper fluid management.
An air chamber is a device used to dampen vibrations and pulsations generated by a reciprocating pump, leading to a more stable liquid flow. By releasing air, the chamber helps minimize pulsations within the pipeline.
Air chambers function in conjunction with throttle valves, through which the liquid flows after leaving the air chamber. The liquid accumulates in the air chamber based on the pressure loss relative to the air pressure.
A pulsation damper serves a similar purpose to an air chamber, aimed at reducing pulsations and vibrations from a metering pump. As fluid is discharged, it enters the damper, which compresses a gas-filled bladder or diaphragm to absorb and mitigate system vibrations. Pulsation dampers promote a smooth and steady flow, and they are compatible with all types of metering pumps.
Calibration cylinders are used to measure the flow rate of a fluid, taking into account factors such as fluid viscosity, the pump’s position relative to the fluid source, and wear on pump components. They are installed on the suction side of the pump, where the drawdown of the fluid column is timed to determine the flow rate and ensure accurate dosing. Calibration should be performed whenever there is a change in fluid properties or alterations in the pump's operation.
The image below illustrates the placement of a calibration cylinder in relation to the valves and the pump within a metering pump system.
Like all pumps, a pressure gauge is used to measure the pressure of a liquid and ensure it remains within specified limits. It acts as a safety device to protect the pumping system from potential damage or explosion due to excessive pressure levels.
The spring of a pressure gauge reacts to compression or expansion to provide a reading in compliance with Hooke’s law of force. Modern pressure gauges are digital and supply numerical readings. They are completely automated and provide readings that can be sent to laptops or desktop computers.
Strainers in metering pumps serve the same purpose as those used in other applications: they filter out particles and debris that could disrupt the pump’s operation. For metering pumps, strainers are positioned before the suction side of the piping. They are particularly useful when drawing materials from the top of a tank, vat, or container where debris might accumulate.
Strainers help remove impurities or potential contaminants from the fluid. The Y configuration is the most common type of strainer used for this purpose.
A degassing valve is used to expel dissolved gases such as oxygen and carbon dioxide from the liquid flow. These trapped gases are vented back to the supply tank. Installed at the highest point in the piping system, degassing valves help prevent gas accumulation that could lead to vapor lock. Degassing connectors are crucial for ensuring the valve system and metering pump function correctly.
Chemical dosing processes often generate gases, including those from substances like sodium hypochlorite, hydrogen peroxide, or sulfuric acid. Movement or compression of these chemicals produces vapors that need to be properly vented.
The images below illustrate examples of installed metering pump systems.
Control volume pumps, injection pumps, feed pumps, dosing pumps, and metering pumps are utilized for injecting chemical additives, proportional blending, and transferring liquids. Their key advantage lies in their ability to precisely control and adjust the flow rate. The efficiency of metering pumps is influenced by their suction and discharge capabilities, which can be fine-tuned by adjusting the stroke length and speed.
Detergent dosing metering pumps are specifically engineered for use in commercial washing machines. They dispense the precise amount of detergent needed for each washing cycle, helping to minimize waste. By preventing blockages in machines, enhancing the efficiency of the laundry process, and safeguarding workers from exposure to detergents and chemicals, these pumps play a crucial role in maintaining operational efficiency and safety.
Automated dispensing of raw materials for packaging represents a streamlined production operation that requires no human intervention. Today, automated packaging systems integrate all stages of the packaging process into a single set of operations, enhancing efficiency.
Challenges with automated dispensing often arise when transitioning between different products. This issue has been addressed with digitally controlled volumetric adjustments, which significantly reduce the time required to switch from one product to another.
Metering pumps are utilized for dispensing chemical mixtures in municipal water supplies and wastewater treatment applications. They are selected for their energy efficiency, which is crucial for optimizing production and controlling energy costs in water treatment plants. By providing precise chemical dosing, metering pumps help water treatment facilities achieve and surpass their operational goals.
Metering pumps are used to inject chemicals such as methanol, monoethylene glycol, and corrosion inhibitors into gas and oil flows. This helps prevent issues like hydrate formation, wax and scale buildup, and corrosion, which can obstruct flow and reduce production efficiency. Additionally, using corrosion inhibitors enhances safety by minimizing the risk of leaks and spills.
Durability is a key requirement for metering pumps in the oil and gas industry. These pumps are designed to be highly resilient, with an estimated lifespan of up to 20 years without needing repairs or replacements.
Center pivot irrigation systems often require the injection of nitrogen into the water supply as it is drawn from a pond, river, or other local sources. The water is directed through pivoting points and applied to crops. Metering pumps are installed at these pivot points to manage the injection process. These pumps can be either portable, allowing them to be used with multiple irrigation systems, or compact enough to remain a permanent fixture at the pivot point.
For irrigation purposes, metering pumps are typically connected to 55-gallon drums containing nitrogen. As the nitrogen is drawn from the tanks, it is mixed with the water and distributed through the sprinkler heads. This system ensures that the nitrogen is effectively applied to the crops while minimizing the risk of it contaminating the groundwater supply.
A metering pump system is engineered to precisely distribute, transfer, and inject specific quantities of fluid into various processes, applications, or operations. The fundamental component of this system is the metering pump, which regulates the fluid volume according to the system’s requirements.
These systems are integral to a wide range of industries, including chemical manufacturing, pharmaceuticals, food and beverage production, water treatment, healthcare, commercial dispensing, irrigation, oil and gas, milling, wastewater management, plastic processing, metal fabrication, automotive, and analytical fields.
There are four primary categories of metering pump systems: diaphragm, bellows, peristaltic, and piston.
A diaphragm system operates with a flexible membrane that oscillates to transfer fluids. When the membrane moves back, it creates a vacuum that draws fluid into the chamber. The volume of fluid is controlled by the stroke length of the diaphragm mechanism. After the desired volume is reached, the membrane moves forward, pushing the fluid out through the outlet valve.
A bellows metering system features a series of interlinked circular membranes that are sealed together. One end of the bellows is connected to the fluid source, while the other end is equipped with a mechanical arm operated by a motor.
As the bellows extend, they draw in fluid until the desired volume is reached. Once the volume is achieved, the bellows compress to expel the fluid through the outlet valve. These systems are ideal for applications needing a constant flow rate at low flow and pressure levels.
A peristaltic metering system utilizes a rotor, tubing, and rollers to manage fluid flow. The fluid travels through the tubing, which is pressed by rollers connected to the rotor inside a sealed housing. As the tubing fills with the fluid, the flow is temporarily halted until the desired volume is reached. The rotor’s rotation then discharges the measured fluid, and the cycle repeats with new fluid entering the tubing. This mechanism allows for efficient and precise fluid transfer.
One key benefit of peristaltic metering systems is their capability to handle dirty or contaminated fluids, which is challenging for other systems. The fluid remains confined within the tubing, which is made from materials resistant to corrosive or harmful substances, thereby avoiding direct contact with the internal components.
The piston metering pump system operates by using the piston’s motion to generate a vacuum that draws in fluid. The volume of fluid pulled into the pumping chamber is directly related to the piston’s stroke length. Once the desired volume is reached, the piston moves forward to expel the fluid through the outlet valve.
In a piston metering pump, the inlet and outlet valves function as check valves, allowing fluid to move in only one direction. As the piston retracts to create a vacuum, the inlet check valve opens, permitting fluid to enter. When the piston advances to discharge the fluid, the inlet valve closes while the outlet valve opens to release the fluid, ensuring a controlled flow.
Metering pumps play a crucial role in dispensing systems. Choosing the right metering pump requires thoughtful evaluation to ensure it meets the specific requirements of the application.
The flow rate is central to the operation of a metering pump and must align with the specific needs of the application. Fluid viscosity affects the flow rate and dictates the stroke force required to transfer the fluid. Flow rate refers to the speed at which the fluid is dispensed, and accurate calculation is crucial for optimal pump performance.
Turndown ratios indicate a metering pump's ability to handle low flow rates while maintaining accuracy. Variations in temperature and pressure during operation can affect pump performance. A well-selected metering pump allows for adjustments to both stroke and drive mechanisms to ensure the desired flow rate is achieved.
Different applications demand varying pressure levels from metering pumps. For example, water treatment typically requires pressures below 100 psi, whereas industries like oil and gas may need pumps that handle pressures exceeding 20,000 psi. Metering pumps are specifically designed to accommodate these diverse pressure needs.
A pump's capacity is influenced by factors such as gear ratio, piston diameter, and motor RPMs. As the piston diameter increases and stroke speed rises, the pressure capabilities of the metering pump generally decrease.
The adaptability of metering pumps is crucial in production environments where dispensing of raw materials and finished products occurs. When product specifications change, the metering pump system must be capable of adjusting and being reconfigured to fit the new requirements.
Metering pumps must be designed to handle varying demands in production settings. While small metering pumps can easily accommodate these changes, larger and more complex systems require careful planning. The specific needs of a production environment significantly impact the choice of metering pump.
In industrial and production settings, metering pumps must be robust, reliable, and durable to handle various operational demands. For applications involving chemicals, corrosives, and toxic substances, it’s essential to select pumps made from materials compatible with these agents. This careful selection process guarantees the pump's longevity and the safety of personnel.
When used under optimal conditions, metering pumps can provide reliable performance for up to twenty years without requiring repairs or replacement. This durability has solidified their role as a critical component in manufacturing processes.
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