Metering pumps are a specific type of positive displacement pump or chemical dosing pump designed for the accurate and precise transfer of fluids.
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The History of Metering Pumps
Pumps have been in use since the time of the Romans, when they were used to raise water. They were important components of both Roman water wheels and water wheels used by the ancient Egyptians, Persians and Indians. After that came the Archimedes screw, a water screw pump named after the classical Greek polymath of the same name. Many historians believe the Assyrians used this pump model to irrigate the Hanging Gardens of Babylon.
In the Middle Ages, because people became interested in mining, scientists developed the suction, or piston, pump. With it, they cleared water from spaces they wished to mine. It used atmospheric pressure to force water into a cylinder, then removed it via an outlet valve. Descriptions of the various types of pumps used at this time can be found in the 1556 work by Georgius Agricola, De Re Metallica.
Throughout the 1800s, scientists, engineers and inventors created a slew of fluid moving pumps that controlled fluid flow in a way that an increasingly industrial world called for them. Pumps like these were used by municipal water supply steam engines, canal boats and more. These pumps controlled flow inherently, but still were not perfect and did not explicitly meter the water they moved.
The metering pump was officially invented in 1936 by Robert Sheen, an industrious man who started off designing and assembling his pumps in his father’s basement. At the time, both he and his father, Milton Roy Sheen, were working for the company now known as GE Water. They sold their products together, and after some initial success, they formed their own company, called Milton Roy Pumps. Their original metering pumps featured a plunger mechanism and a crank-driven piston. While they allowed for flow rate adjustment, they were vulnerable to leaks and therefore also prone to inaccuracies. This is because the pumps were single pumps and the liquid made direct contact with the piston. Metering pump manufacturers were later able to fix this issue by using a diaphragm to divide the pump into two chambers and isolate the piston from the fluid. In addition to using diaphragm pumps, they switched over to all non-corrosive pump materials, such as PTFE lining, which kept the parts intact and the fluids clean.
During the 1970s, an Ohio company called Gorman-Rupp came out with the first ever bellows metering pump. During that decade, engineers also created the first metering diaphragm pumps that worked using solenoid coils. The solenoid coil flexed the diaphragm by magnetizing it. This made metering pumps operational using electronics. With fewer parts and easier operation, they also became less expensive, easier to maintain. The only problem with this pump was that it could not run at slow speeds. This limited its use, accuracy and working life. Engineers were eventually able to fix this with the advent of new technology, such as digital and CNC dosing control. Today, with continuing technological advancements, fluid transfer pumps are utilized in any number of metering systems and lauded for accuracy and precision.
Advantages of Metering Pumps
The wide use of metering pumps is largely reflective of the many benefits they offer. High accuracy dispensing, high system pressure, low flow rates in GPH or mL per hour, the capacity to handle hazardous or corrosive fluids and controlled dispensing that can even be metered by a microprocessor or computer are all common advantages of metering pumps.
Metering Pump Design
- Pump Materials
- Typically, metering pump manufacturers construct the pump with anti-corrosive and durable metals, like stainless steel, or plastics like PTFE.
- Considerations and Customization
- When designing a custom metering pump or selecting the appropriate model for a customer, manufacturers must decide on a number of design specifications, based on customer needs. These include: motor capacity, stroke length, the maximum discharge pressure rating, temperature rating, flow rates, pump apparatus, motor capacity, fluid composition and viscosity, and the degree to which the membrane, piston or bellows can be extended.
- The type of liquid in use is extremely important as it has a profound impact on the functionality of the pump. Most liquids can be only slightly compressed, allowing for easy displacement. The introduction of gaseous bubbles, however, makes displacement more difficult as the air may be able to withstand a great deal of compression, perhaps even beyond the capabilities of the pump therefore leaving it ineffective at expelling the fluid.
- Based on these considerations, manufacturers can design or choose the right metering pump for you. To meet the supply of various industries metering pumps are extremely diverse, and most can be adjusted to suit individual tasks.
- While the means of motion may vary significantly, all metering pumps are composed of relatively few parts. These include: a pump head, a fluid reservoir, hoses and tubes, an intake check valve, an exhaust valve, a main body, a diaphragm, bellows or a piston and a motor or manual pedal.
- The pump head is a cylindrical cavity which houses the fluids just before they are displaced. A fluid reservoir of variable size is connected via hoses or tubes to an intake check valve (such as one of those offered by these companies) and attached to the pump head. Opposite the intake point is the exhaust or outlet valve which is connected, again through the use of tubing or hoses, to the main body, which holds the process flow to which the fluid is introduced. Each valve has the ability to flow only in one direction. The pump head also houses the diaphragm, bellows or piston that will enact motion, drawing the liquid in and expelling it. A motor or manual pedal is attached to this component depending on the specific design. Bellows and peristaltic pumps differ somewhat in design, but follow the same general operation.
How Metering Pumps Work
Metering pumping is a two part process. The first action is the suction, or intake stroke. At this point, the membrane or piston is withdrawn or the bellows extended. This action creates a vacuum effect which opens the inlet valve and pulls the fluid, be it oil, water, syrup or any other material into the pump head.
The second part takes when suction ceases and the inlet valve closes. The motor or manual operator then extends the membrane piston, or compresses the bellows in towards the fluid which is then compressed as much as is possible and pressurized. This pressure forces open the outlet valve and the liquid is expelled from the pump head due to displacement.
Types of Metering Pumps
There are two main types of metering pumps used for variable fluid metering. These are called variable displacement constant speed pumps and fixed displacement variable speed pumps.
- Variable Displacement Constant Speed Pumps
- Adjust the displacement, or the stroke, in order to control the amount of liquid pumped per minute. These differing amounts of liquid are always precise. Variable displacement constant speed pumps, as well as displacement variable speed pumps, have the capacity to produce an unending continuous flow of metered fluid into an expulsion unit, be it a dialysis machine or beverage dispensing unit.
- Fixed Displacement Variable Speed Pumps
- Allow consumers to adjust the motor speed or cycle frequency in order to enact change in the flow rate. The ability to adjust the stroke involves a more complex mechanism and a larger unit to allow for greater fluid transmission. For this reason, the fixed displacement variable speed type of metering pump is often preferred and commonly seen in industrial and commercial applications.
- In addition to these, several different metering pump mechanisms are used to achieve the movement of exact amounts of fluid. Examples include: micrometer adjustment screw pumps, pneumatic metering pumps, electronic metering pumps, bellows pumps, centrifugal pumps, chemical metering pumps, diaphragm metering pumps, dispensing pumps, drum pumps, electronic metering pumps, fluid transfer pumps, gear pumps, liquid pumps, peristaltic pumps, positive displacement pumps, piston metering pumps and small metering pumps.
- Micrometer Adjustment Screw Pumps
- Metering pumps that receive assistance from micrometer adjustment screws. These help them alter their flow rate(s). This type of metering pump is quite common.
- Pneumatic Metering Pumps
- Offer an alternative way to adjust flow rates, namely by pneumatic actuator process signal.
- Bellows Pumps
- A specific type of metering pump which use accordion-like pleated materials to enact the positive displacement of fluids. In many applications this type of pump is preferred even to the more traditional piston metering pump as it offers high reliability and clean operation.
- Centrifugal Pumps
- Use a revolving disk attached to a drive shaft that transports fluid without pulsation as it spins.
- Chemical Metering Pumps
- Precise instruments used to move chemicals. Chemical metering pumps can be used to transport any number of chemical materials, including: acids, bases, corrosives, viscous fluids and slurries.
- Diaphragm Metering Pumps
- Employ flexible membranes to alter the volume of a controlled chamber. The flexible membranes do so by initiating motion while piston metering pumps use a cylindrical plunger. The goal of diaphragm metering pumps is to effectively displace fluids with accuracy and precision.
- Dispensing Pumps
- Designed to dispense a precise amount of liquid or gas.
- Drum Pumps
- Metering pumps used to remove fluids from drums, barrels, tanks, etc.
- Electronic Metering Pumps
- Fluid transfer pumps that operate off of electrical currents. These currents power the actuating devices responsible for the pumping action of a metering pump. They adjust flow rates per electronic actuator signals, and they increase the user’s ability to employ computer and other automated programming in order to adjust flow rates throughout processing.
- Fluid Transfer Pumps
- Encompass a broad range of devices designed with the intent to move any number of fluids from one place to another without specific concern for the modulation or transfer of power associated with this motion.
- Gear Pumps
- Use gears to trap fluid between the teeth of two or three rotating gears. Gear pumps are ideal for high system pressure applications and are typically magnetically powered.
- Liquid Pumps
- Such as water pumps, use displacement to move fluids from one place to another.
- Metering Systems
- Include all apparatus implicated in the precision transfer of carefully measured fluids through positive displacement. Systems such as these are responsible for the maintenance of process streams of variable chemical composition and monitor liquid flows.
- Metering Equipment
- Includes any number of devices used in the metered pumping of precisely measured fluids from an area of high pressure to an area of low pressure.
- Peristaltic Pumps
- A unique type of metering pump used to move fluids from one place to another. They are unique because they carry out their function using rubber tubing compressed by rollers that mimic the same contracting and relaxing motion that the gastrointestinal tract used to move fluids.
- Positive Displacement Pumps
- Transfer liquids and gases from an area of high pressure to an area of low pressure.
- Piston Metering Pumps
- Use a reciprocating plunger to displace liquid through the machine. A rigid piston assembly gives them the maximum pressure and accuracy of metering pumps.
- Small Metering Pumps
- Miniaturized positive displacement units designed for the movement or transfer of exact amounts of fluid with extremely accurate flow rates. While ‘small’ is a relative term, it can describe the physical size of metering equipment, which may weigh as little as 39 grams or a low flow rate.
Metering Pump Applications
Also known as proportioning, controlled-volume and dispensing pumps, these liquid process meter pumps are highly praised for their ability to move exact amounts of fluid in a given time frame with extreme accuracy and reproducibility.
Many industries utilize metering pumps for their unique ability to cyclically introduce a consistent amount of fluid into a continuous-flow stream ensuring homogeneity.
Far from limited, metering equipment is commonly found in industries such as: pharmaceuticals, food and beverage processing, water treatment, medical, commercial vending, irrigation, petroleum, chemical engineering and processing, milling, sewage, plastic fabrication, metalworking and laboratory.
Standards and Specifications for Metering Pumps
Depending on your location, industry or application, your metering pumps may be subject to a variety of different standard requirements. In addition, there are a number of standard guidelines out there that, while not necessarily required, signal high quality. Examples of such standards include those put out by: ANSI, NEMA, ATEX (used in the EU), the FDA and the military (Mil-Specs). Learn what metering pump standard certifications you should seek by talking to your industry leaders.
Things to Consider When Purchasing Metering Pumps
If you reached us via a web search, you have probably noticed that the market is flooded with metering pump manufacturers. While we love choice, information overload often makes it hard to make the right decision. Because we know how important the right manufacturer is, we’ve put together a list of those metering pump companies we have found to be the most reliable, experienced and skilled. You’ll find their information by scrolling up towards the top of this page.
Before you begin browsing, we recommend you take some time to jot down a list of your specifications, questions and concerns. Make sure to include things like: standard requirements, your budget, the date by which you need your metering pumps, your delivery preferences and your post-delivery support preferences (installation assistance, maintenance help, etc.). After you make your list, check out ours. Check the services and products offered of those we’ve listed against your requirement list. Pick out three or four to whom you’d like to speak, then reach out to them to discuss how they may help you. After you’ve spoken with each of them, compare and contrast your conversations and their offered services. Finally, choose the right one for you based on who can provide the most closely tailored quality services within your budget.
Metering Pump Accessories
Metering pump accessories are ideal solutions for increasing the accuracy and efficiency of the metering pump when dispensing materials. Common metering pump accessories include: injection valves, calibration cylinders, strainers, pressure control valves, inline pressure relief valves, pulsation dampeners and foot valves.
Metering Pump Terms
- Air Bound
- The situation in which a centrifugal pump is filled with air, which prevents a vacuum from forming. In this case, water will not flow through the pipe.
- Back Pressure
- The amount of pressure a pump is required to overcome to dose at the point of injection, measured in bar.
- The water handling ability of a water pump.
- A situation in which vacuum pockets form in a pipe, eventually causing the pipe to implode.
- Dead Head
- A situation in which a pump attempts to run against a closed valve or against any other condition preventing discharge.
- Discharge Hose
- A hose that moves the discharged water from the pipe.
- Drain Plugs
- Plugs that are removable from the pipe, used to drain water during inactivity.
- Electronic Controller
- An entire control system that supplies feedback to the pump to sustain the accurate chemical dosage, which can increase efficiency.
- Flooded Suction
- A condition wherein a pump is located below the liquid being pumped.
- Flow Switch
- A device that supplies a positive indication that the fluid is flowing and the pump is running.
- Metering Pump Accessories
- Metering pump accessories are products that will increase the performance or accuracy of the metering pump.
- Force applied per unit area.
- Creation of a vacuum in a pump.
- Pump Housing
- The casing of the pump, made of plastic, stainless steel, aluminum or iron.
- Pumping Level
- The lowest level of water during the pumping process.
- Shock Mounts
- Rubber mounts that are used to help control a pump’s vibration.
- A filter at the end of the suction hose that prevents large objects from entering.
- Thermal Overload Sensor
- A sensor in a pump that shuts down the system when the operating temperature exceeds the limit of safety.
- The degree to which a fluid resists flow when pressure is applied.