Last month in part 1 of this series, we examined the myriad chemicals that can be used in wastewater-treatment systems, knowing that each one contains unique handling and implementation characteristics that must be followed to the letter. Plant operators must be certain that they have selected the proper metering pump technology for their dosing applications. With that in mind, here’s a look at four pump technologies that can play a key role in an optimized wastewater-treatment operation if implemented properly.
Featured Image: Hydraulically actuated diaphragm metering pumps are a leading technology of choice for wastewater-treatment plants because they can handle the hardest chemicals, can pump against extremely high pressures, offer highly repeatable dosing accuracy, and have been designed for twenty years of service.
MECHANICAL DIAPHRAGM METERING PUMPS
Mechanically actuated diaphragm metering pumps offer an ease of operation and start-up that makes them an attractive alternative for many applications. They normally offer a lower initial cost than other motor-driven metering pump designs, especially at higher flow rates, but can have higher operating costs.
These pumps offer excellent suction-lift capabilities and also provide the ability to handle liquids that off gas, such as sodium hypochlorite, and more viscous chemicals since the diaphragm is attached to the piston for a positive return usually aided by a spring. They are somewhat limited in discharge pressure capabilities with many being around 100 to 150 psi (7 to 10 bar) max. Repeatable accuracy is normally about +/-2 percent. They are generally not offered with an on-board relief valve, so an external relief valve is usually required to prevent damage to the pump in an over-pressurized situation.
Solenoid-actuated diaphragm metering pumps are a viable choice in chemical-dosing applications at wastewater-treatment facilities because they offer highly reliable dosing accuracy, even when working with extremely low flow rates and operating pressures.
HYDRAULIC DIAPHRAGM METERING PUMPS
Hydraulically actuated diaphragm metering pumps are ideal for operation in the harshest chemical-handling conditions as they are a low-maintenance pump that is designed for twenty years of service. This longevity and low maintenance is largely due to most of their moving part being submerged in a bath of hydraulic fluid coupled with fact that the diaphragm is hydraulically balanced. Hydraulically balanced means that the hydraulic fluid is on the oil side of the diaphragm while the chemical being pumped is on the other side (wetted or process side) of the diaphragm. The piston, internal to the pump, pushes oil against the diaphragm but never comes in direct contact with it. These pumps are capable of pumping against extremely high pressures, if need be, so long discharge lines are not a problem.
Because many pump manufacturers also design the other components that make up a complete chemical-feed system, they can be a significant source of assistance, or even a provider of comprehensive turnkey systems, for wastewater-handling operations.
Hydraulic diaphragm pumps are equipped with an adjustable internal relief valve that prevents an over-pressurized situation from happening and damaging the pump. They also offer a repeatable dosing accuracy of +/-1 percent.
SOLENOID DIAPHRAGM METERING PUMPS
Solenoid actuated, or electronic, metering pumps are a viable economical option in wastewater treatment operations for low-flow/low-pressure chemical-dosing applications. They are generally available to a maximum of 20 gallons per hour and at those capacities maximum pressures are normally about 30 psi (2 bar). The lower and medium capacities are compatible with pressures of 100 to 150 psi with low flows (less than 1 gallon per hour) to over 200 psi (14 bar). They offer a repeatable dosing accuracy of +/-3 percent. They are normally provided with an on-board relief valve to prevent pump damage from over-pressurization.
PERISTALTIC PUMPS
This pump technology, simplistic in its design, is perfect for handling viscous and abrasive chemicals. Because the design features a rotor with shoes or rollers that squeeze the hose or tube and force the liquid to the discharge port, peristaltic pumps are able to run dry, a feature that competitive technologies like progressive cavity pumps can’t provide because their rotors and stators will be damaged in run-dry conditions.
Peristaltic pumps also do not have valves that can become clogged. This is an important consideration when the pump needs to be shut down during a product run; the lack of valves in the peristaltic pump eliminates any clogging issues, especially when handling viscous liquids or those that will solidify or become gelatinous when resting. This also makes the peristaltic pump ideal for the handling of abrasive or corrosive chemicals.
Peristaltic pumps are ideal for various chemical-handling applications in wastewater treatment because their simplistic design and operation allows them to reliably handle both viscous and abrasive chemicals.
While all of these pump technologies can provide an unquestioned list of benefits for the wastewater-treatment plant operator, it is still a challenge to know exactly which pump is best for which chemical-metering application. This is where the pump manufacturer can lend a hand. Many pump manufacturers also design and manufacture many of the components that are included in a complete chemical-feed system, i.e. relief and back-pressure valves, calibration columns, tanks, mixers, injection quills, and control panels. Some even offer the complete chemical-feed systems as an option and possess the capability to build a system that meets the specific needs of the treatment plant.
Who better to provide the system than the manufacturer of its components? So, while the task of properly outfitting a treatment facility may be overwhelming, the manufacturers of the various components that will be used to optimize the system, or the manufacturer of a complete system, can be a significant source of assistance in determining how to best outfit the plant.
CONCLUSION
Ensuring that communities have the cleanest water possible for cooking, cleaning, drinking, bathing, and recreational activities like fishing and boating places a great amount of pressure on water and wastewater-treatment facilities to perform their jobs as effectively, efficiently, and safely as possible. The number and type of chemicals that may be required in the various treatment processes only help to increase the risk for the plant operator.
Therefore, the operator can only be certain that the operation reaches the pinnacle of proper performance if the best pump technology is chosen for each of the many critical chemical-metering processes that must take place every day.
With so many varying flow rates, viscosities, compatibility issues, pH levels, and handling characteristics to consider, a varying array of pump types must be employed to guarantee optimized operation. When it comes to chemical handling, mechanical, hydraulic, and solenoid metering pumps, along with peristaltic pumps, have been proven to offer the best operational capabilities. When used in the proper application, these technologies can help overcome any concerns the plant operator can have—and the pump manufacturers themselves stand ready to lend a hand in order to ensure that the treatment system will reliably operate at the highest level.
About The Author
Tom O’Donnell is director of business development for Neptune™ Chemical Pump Company and PSG®. He can be reached at 215.699.8700, ext. 3327, or tom.odonnell@psgdover.com. Based in North Wales, Pennsylvania, Neptune is a leading manufacturer of chemical metering and peristaltic (hose) pumps, chemical feed systems, chemical injection accessories, make-down systems, and industrial mixers. Neptune is a product brand of PSG®, a Dover company, Oakbrook Terrace, Illinois. PSG is comprised of several of the world’s leading pump companies, including Abaque®, Almatec®, Blackmer®, Ebsray®, EnviroGear®, Griswold™, Mouvex®, Neptune™, Quattroflow™, RedScrew™, and Wilden®. For more information, visit www.neptune1.com and www.psgdover.com.
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MODERN PUMPING TODAY, June 2017
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