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A metering pump moves an accurate volume of fluid in a specified time period providing a precise flow rate. Although this equipment can pump water, it is often used to pump chemicals, solutions, and other liquids. This kind of pump is rated to be able to pump into a high discharge pressure. It is designed and made to meter at practically constant flow rates when averaged over time within a wide range of discharge pressure. Many manufacturers provide each of their models of metering pumps with a maximum discharge pressure rating, depending on what they were made to pump against. Therefore, an engineer, designer, or any user should ensure that the pressure and temperature ratings and pump materials are compatible for the application and the type of liquid being pumped. So, how does a metering pump work? Also called an oscillating positive displacement pump, a metering pump has a pump head and a motor, which is commonly an electric motor. It sucks in a defined fluid volume with the backstroke of the displacer then presses it into the dosing line with the pressure stroke. In other words, the fluid being pumped goes through the pump head, entering through an inlet line and leaving through an outlet line. Types of metering pumps and their uses One of the most common metering pumps is the piston pump. This is a positive displacement pump usually designed to pump at practically constant flow rates averaged over time against a wide range of discharge pressure, high discharge pressures of thousands of pounds per square inch (psi) included. Another type of metering pump is used in high-pressure chromatography such as HPLC and ion chromatography. This type is much like small piston metering pumps. The piston used for this type of pump is usually made of artificial sapphire. Its ball check valves may also have ruby balls and sapphire seats. This is to for wear resistance and chemical resistance to solvents. A diaphragm pump is used for metering to avoid leakage at the packing or seal most especially when the liquid is dangerous, toxic, or noxious. This pump has a diaphragm through which repeated compression/decompression motion is transmitted. Liquid does not penetrate through the diaphragm. Hence, the liquid inside the pump is completely sealed off from the outside. This pump is ideal for high-accuracy applications such as pH/ORP control. A peristaltic pump use motor-driven rollers to roll along flexible tubing which compresses it to push forward liquid inside. Although a peristaltic pump can be used to meter at lower pressures, the flexible tubing is only limited in the level of pressure it can withstand. Be reminded that one of the advantages of this pump is non-contaminating. It is also available in a wide variety of pump materials.
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