by Rebekah Fuller, IQS Editor
Ever stop and think how that delightful cappuccino gets from the machine and into your cup without making a huge mess? It’s the little dispensing pump that controls the amount of the delicious liquid ejected from the nozzle each time. This small metering pump comes in handy, especially if you’re like me and ignore the “Fill until ¾ full” sign, pushing the button for short bursts after my cup’s almost full so I’m satisfied with how much I have. The same kind of controlled-volume liquid transfer devices are used in soda fountain pumps. Obviously, the activation for these electronic metering pumps is the push-button switch that we employ when we want our favorite hot or cold drinks.
Besides commercial vending applications, metering pumps are utilized in an array of operations that require accurate and precise transfer of fluids. This is the whole point of metering pump systems—to move exact amounts of fluid in a given time frame with extreme accuracy over and over again. This kind of equipment is vital in a number of industries, such as chemical, pharmaceutical, food and beverage processing, water treatment, medicine, automotive, semiconductor, irrigation and agriculture, oil and gas production, cryogenics, pulp and paper manufacturing, plastic fabrication, metalworking and more. Metering systems dispense exact amounts of medications to patients over a period of time, controlling the flow rate for continuous succession of small doses as ordered by the doctor. Electric medical metering pumps need to have a backup generator or battery to ensure unbroken flow.
Not as important as life and death, but necessary for successful business as a food and drink manufacturer, is the right mixture of ingredients so as not to assault consumers’ senses. Our taste buds tell us when there is not enough syrup in our fountain drink, and how much more important is it for manufacturers when producing mass batches bottled day in and day out? And delivering too much or too little of certain liquids at incorrect intervals can really mess up chemical and pharmaceutical processing with disastrous results. What would we do without metering equipment?
From dialysis machines to beverage dispensing units to agricultural pesticide delivery systems and industrial applications that include internal mechanical lubrication; solvent, detergent and rinse agent dispensing in laundry, warewashing and other appliances; ink and pigment transfer for paint formulation, printing and textiles—the modern world cannot do without the metering pump. Think about the consumer products you have at home contained in tubes, bottles, jars, jugs and any number of containers with small openings. You can bet that pumps of some kind (also centrifugal feed pumps, controlled gear pumps and vacuum pumps) were used to mass-process the contents into each container…much more efficient than rows upon rows of human laborers pouring liquids of various viscosities through funnels.
Metering pumps can only be used with liquids because these substances are nearly incompressible; therefore, able to create the needed pressure for easy displacement, lending to the name positive displacement pumps. Liquids of all thicknesses and even pastes are viable materials. The traditional toothpaste tube is filled after the tube has been capped. The often minty mixture is inserted from the opposite end then crimped closed. The general operation of a metering pump involves suction of the substance into the pump head from a tubing or hose system through an inlet valve. The motion of a diaphragm, bellows or piston causes the suction, and an opposite motion once the specified amount of liquid is present creates the pressure for the pumping mechanism to precisely release the contents from the exhaust valve. Electricity, pneumatics, hydraulics, fuel or manual power can be used to generate the pumping motion. Electrical current is highly popular with today’s integration of digital and computerized automation, allowing for easy adjustments to be made without interrupting the fluid flow or cycle, as in variable displacement constant speed pumps or fixed displacement variable speed pumps. These precision adjustment options for flow rate and amount of fluid transfer per revolution or stroke allow for greater flexibility and complexity in dosing and injecting applications.
Metering pump manufacturers can build their products with the capacity to handle hazardous and corrosive fluids or fluids that need to remain sanitary. A peristaltic pump maintains safe transfer of food products, beverages, pharmaceuticals, biomedicals, cosmetics, chemicals and microbial treatments because the fluid only comes in contact with the tubing. Thorough research on the specifics of a pump needs to be done before purchase, as far as what materials it can handle and what its capacity is for volume, speed and pressure. When a pump is working correctly there should be no leakage or slippage anywhere. The presence of gaseous bubbles decreases the pump’s ability to expel the fluid, making displacement ineffective or even impossible. Check out various metering pump accessories—like automatic degassing valves—that help with this potential problem. Other items include calibration cylinders, pressure relief valves, pulsation dampeners, injection quills and corporation stops.