22 Oct How Dosing Pumps work and some Typical Uses
Most pumping equipment is required to generate a continuous stream of liquid, transporting it between the source and the point of use. For example, feedwater is delivered to a boiler in this manner, and drinking water is distributed to homes and businesses in the same fashion. However, on occasions, there is a need to deliver precisely measured quantities of a fluid, for example, when adding a reagent to initiate some chemical process. In such cases, dosing pumps are frequently the tools of choice. A device must produce and isolate equal volumes of liquid during its operation to dispense a measured amount of fluid.
Four main types of equipment are available for this purpose, and each achieves the measuring step differently. Which of these may be most suitable will depend on the details of the task to be undertaken. Such factors include temperature, pressure, viscosity, and the properties of the chemicals to be handled. Regardless of which type of unit may be required for a given job, the dosing pumps generally form part of a more elaborate chemical metering system. A suitable container will be necessary to hold the chemicals to be added. An injector with a one-way valve may also be required to overcome possible back-pressure when injecting the dose into a pipeline. To control the operation, a manual switch or a timing mechanism might suffice in many instances. However, the entire process could also be automated, using a combination of integrated sensors and controls to coordinate multiple pumping devices handling different chemicals.
In practice, two of the four common types of dosing pumps employ a diaphragm to produce a metered volume of fluid. The first of these is designed to operate continuously. Its chamber is filled and emptied by the action of a piston attached to the diaphragm. Once the pump’s chamber is full of liquid, the inlet valve closes, the outlet valve opens, and the piston proceeds to eject the measured dose at a constant flow rate. Typically, these units can generate a flow rate of between 6 and 250 litres per hour.
The variant of these constant-flow dosing pumps also relies on a diaphragm. The latter moves back and forth in response to a solenoid which results in a pulsed flow. The time interval between successive pulses will determine the volume of the dose. These units are less accurate than the piston-operated type. However, when accuracy is not crucial, their design is much simpler. They are also significantly less expensive.
The third variety of these devices employs a set of meshing gears that act as impellers. These lobe-type units trap fixed volumes of fluid in the gaps between their teeth. Like other dosing pumps, they rely on a system of valves to regulate the dose. However, their design makes them vulnerable to wear and tear, which can affect their accuracy. Consequently, these units work best when used with viscous fluids, which tend to act as lubricants, helping to reduce this tendency to wear.
Finally, the fourth type employs a process that mimics the action of the intestine required to maintain the continuous movement of food during the successive stages of digestion. This action is known as peristalsis and has been adapted to create aptly-named peristaltic dosing pumps similar to those used to aerate tropical fish tanks. The fluid is drawn through a flexible tube by rollers that compress it to form discreet volumes of liquid. Those volumes are determined by the internal diameter of the tubing and the distance between rollers. However, although these peristaltic devices are highly accurate, they tend to wear out quickly. Also, they are not suitable for use in high-pressure applications.
There are many possible uses for these units across a wide range of industries. For example, water treatment plants rely heavily on dosing pumps to ensure the water delivered to our homes and businesses is safe and palatable. During the early stages of processing, they are used to add chemicals to adjust pH and assist the sedimentation process. Later, the potable water must be dosed with an accurate measure of chlorine to maintain sterility during distribution. In healthcare, miniature peristaltic units are sometimes employed in automated analysis equipment used by biomedical laboratories.
Prochem is an industry leader in the design and manufacture of pumping equipment and has almost thirty-five years of experience. The company produces a wide range of world-class products, including dosing pumps for most purposes.