The most comprehensive guide to metering pumps

Thread Content

1. Definition of a metering pump: A metering pump is a special type of positive displacement pump that can meet the requirements of various stringent process conditions; its flow rate can be adjusted continuously within a range of 0-100%, and it is used for transporting liquids, especially corrosive ones. A metering pump is also known as a dose pump or proportional pump. A metering pump is a reciprocating positive-displacement pump used for precise measurement, and it is generally required that its accuracy and stability be within ±1%. As modern industry continues to develop toward automated operations and remote control, the advantages of metering pumps, such as their strong compatibility and wide range of suitability for various media (liquids), become particularly prominent. A metering pump is also known as a dose pump or proportional pump. A metering pump is a special type of positive displacement pump that can meet the requirements of various stringent process workflows; its flow rate can be adjusted continuously within a range of 0-100%, and it is used for transporting liquids, especially corrosive ones. A metering pump is a type of fluid transfer machinery, and its key feature is its ability to maintain a constant flow rate regardless of the discharge pressure. Using a metering pump allows for the simultaneous performance of pumping, metering, and regulating functions, thereby simplifying the production process. By using multiple metering pumps, several fluids can be fed into the process flow in precise proportions for mixing. Due to its outstanding advantages, metering pumps are now widely used in various industrial fields such as petrochemicals, pharmaceuticals, and food processing. 2. Classification of metering pumps: 1) Based on the flow-through component: (1) Plunger/piston type; (2) Mechanical diaphragm type; (3) Hydraulic diaphragm type. 2) Based on the driving method: (1) Motor-driven; (2) Electromagnetically driven. 3) Based on the operating mode: (1) Reciprocating type; (2) Rotating type; (3) Gear-type. 4) Based on pump characteristics: (1) Extra-large frame; (2) Large frame; (3) Medium frame; (4) Small frame; (5) Miniature frame. Other classification methods include electric-controlled type, pneumatic-controlled type, insulated type, heated type, high-viscosity type, etc. 3. Structure of metering pumps: Such pumps consist of three parts: a motor, a transmission box, and a cylinder body. The transmission box components consist of a worm gear mechanism, a stroke adjustment mechanism, and a crank-slider mechanism ； A high adjustment stroke is achieved by rotating the adjustment handwheel, thereby changing the eccentricity of the moving shaft in order to modify the stroke of the plunger (piston). The cylinder block components consist of the pump head, suction valve assembly, discharge valve assembly, plunger, and packing seal. 4. Working principle of the metering pump: The motor drives the worm through a coupling, and the worm gear reduces the speed, causing the main shaft and the eccentric wheel to rotate. The eccentric wheel then drives the sliding adjustment seat of the bow-shaped linkage to move back and forth. As the plunger moves toward the rear dead center, a vacuum gradually forms within the pump chamber; the suction valve opens, allowing liquid to be drawn in ； As the plunger moves toward the dead center, the suction valve closes while the discharge valve opens, and the liquid is discharged as the plunger moves further. The reciprocating motion of the pump enables continuous, pressurized, and quantitative discharge of liquid. The flow rate of the pump is adjusted by rotating the adjustment handwheel, which in turn causes the adjustment screw to rotate; this changes the distance between the arc-shaped links, and as a result the stroke of the plunger (piston) within the pump chamber is altered, thereby determining the flow rate. The scale on the adjustment handwheel determines the plunger stroke, with an accuracy of 95%. 5. Features of metering pumps ⒈ These pumps have excellent performance; the diaphragm-type metering pumps do not leak at all, offering high safety levels and precise metering. The flow rate can be adjusted arbitrarily within the range from zero to the maximum set value, while the pressure can be selected anywhere within the range from atmospheric pressure to the maximum allowable level. ⒉The adjustment is intuitive and clear; it operates smoothly without noise, is compact in size and light in weight, is easy to maintain, and can be used in parallel. ⒊This pump comes in a wide variety of models, offering comprehensive performance; it is suitable for transporting fluids at temperatures ranging from -30 degrees to 450 degrees, with viscosities of 0–800 mm/s. The maximum discharge pressure can reach 64 Mpa, while the flow rate ranges from 0.1 to 20,000 L/h. The measurement accuracy is within ±1%. ⒋As required by the process, this pump allows for manual and variable-frequency adjustment of flow rate, as well as remote control and automatic computer-based control. 6. Introduction to the models of metering pumps: Hydraulic diaphragm, transmission mechanism. (1) Power from the motor is transmitted to the worm and worm gear to achieve reduced-speed rotation, which in turn causes the crankshaft and connecting rod mechanism to move back and forth, thereby driving the plunger to generate hydraulic force. ⑵ The stroke adjustment mechanism consists of a crankshaft, an eccentric wheel, an adjustment nut, an adjustment screw rod, an adjustment handwheel (handle), a dial (pointer), and a scale, and it achieves the relative stroke of the plunger by changing the eccentricity. Hydraulic system ⑴: The hydraulic system of the hydraulic diaphragm metering pump, whose structure consists of a plunger, cylinder body, cylinder head, inlet and outlet valves, as well as a hydraulic diaphragm and three valves (namely: vent overload valve, limit valve, and compensation valve). In operation, the diaphragm separates the hydraulic oil from the medium, which gives the hydraulic diaphragm metering pump the advantage of being leak-free. ⑵In a hydraulic diaphragm metering pump, the plunger at the hydraulic end operates as driven by the reciprocating motion of the crank-slider mechanism at the drive end. The plunger moves back and forth within the hydraulic chamber, causing changes in the pressure of the hydraulic oil; these pressure changes lead to flexural displacement of the hydraulic diaphragm, thereby enabling the transfer of fluid. The relative stability of the amount of hydraulic oil in the chamber is maintained by the function of the three valves. ⑶ The overload valve automatically expels the gas that enters the hydraulic chamber from the hydraulic oil, ensuring smooth operation. It prevents overpressure from occurring due to an excess amount of hydraulic oil or a blocked discharge pipeline, thereby automatically activating the overload valve to serve as a protection mechanism. ⑷ The limit compensation device opens the limit valve by means of a hydraulic diaphragm, and replenishes oil as needed based on the vacuum level in the hydraulic chamber, thereby ensuring that the hydraulic chamber is always filled with hydraulic oil. Electromagnetic diaphragm: An electromagnetic metering pump uses an electromagnetic plunger to drive the diaphragm to move back and forth inside the pump head, thereby causing changes in the volume and pressure within the pump chamber. These pressure changes trigger the opening and closing of the suction valve and the discharge valve, allowing for the precise intake and discharge of liquid. 　An electromagnetic metering pump is a type of metering pump driven by an electromagnet, designed for transporting liquids in pipelines with low flow rates and low pressure. It is popular in the industry due to its simple structure, low energy consumption, accurate metering, and ease of adjustment. Its design principle is \"simplicity and practicality\", but its drawback is the low flow rate it can handle (which is common)