Tom O'Donnell is director of business development with Neptune and PSG. He may be reached at 215-699-8700 or firstname.lastname@example.org. Based in North Wales, Pennsylvania, Neptune Chemical Pump Co. is a manufacturer of chemical metering and peristaltic (hose) pumps, chemical feed systems, chemical injection accessories, makedown systems and portable mixers. Neptune is an operating company within PSG, a Dover company. You can find more information on Neptune at neptune1.com and PSG at psgdover.com.
Flooded suction is always preferred since it is easier to prime the pump, plus there is less chance of a starved suction condition. Limiting the suction piping to 6 or 7 feet and making sure the suction piping is of adequate size for the metering pump is equally important. A suction strainer will trap any impurities in the chemical supply while preventing any dirt or debris from getting to the metering pump’s ball checks. Isolation valves can placed in both the suction and discharge piping of the metering pump in order to isolate it. A calibration column (drawdown cylinder) mounted in the suction line can be used to calibrate the metering pump.
Many pumps are provided with internal relief valves, but external relief valves are always recommended to be mounted in the pump discharge and piped back to the supply tank. Back-pressure valves are necessary when the metering pump does not have a back-pressure device or the system does not have back pressure. Check valves in the discharge piping will prevent backflow. A pressure gauge can be placed in the discharge piping in order to view system pressure. A pulsation dampener will provide smooth, laminar flow and prevent water hammer. Injection quills make sure the chemical is adequately dispersed. A control panel with NEMA-rated enclosure (12, 3R, 4, 4X, 7) and a main disconnect that features Hand or Auto mode (HOA), or on/off switches with running lights will provide local control for the system.
All of these recommendations and components need to be reviewed when the chemical feed system is being designed, and who better to be able to size and select them than the designer of the system and the manufacturer of the components?
With all of this in mind, design engineers should realize that no one is better qualified to assist in and successfully integrate pumps and components into a chemical-feed system than the designer and manufacturer of those pumps, mixers and components. Because of their familiarity with the system and its components, the manufacturers are also able to remediate any maintenance and repair needs quickly—often with the ability to solve an operational problem with a single phone call.
So, the overriding question for the facility operator becomes: what is the best way to construct a complete chemical-feed system for use in a power plant, using components that are acquired from a hodgepodge of suppliers, or creating one with components that come from a single-source manufacturer, the one that actually builds the system’s pumps, mixers and other equipment?
The answer should be obvious. When building a chemical feed system for use in power generation—the reliable operation of which is imperative to the creation of indispensable electricity for use in the national power grid—it’s best to rely on the expertise and experience of the manufacturer of the actual equipment, someone who has the knowledge to build the system correctly and the ability to quickly solve any problems that may arise.
3 Types of Diaphragm Pumps
Hydraulic diaphragm metering pumps: Hydraulically actuated diaphragm metering pumps are designed to handle the harshest chemicals. Because they are hydraulically actuated, they are able to inject chemicals at extremely high pressures. Pressures up to 3,000 or 4,000 pounds per square inch (psi) are not uncommon in power plant boiler water treatment applications. These are low-maintenance pumps because most of their moving parts are submerged in a bath of hydraulic fluid, which allows them to provide at least 20 years of service.
Mechanically actuated diaphragm metering pumps (motor-driven): Designed for low-pressure application, normally less than 250 psi, they offer ease of operation and startup, but can have higher operating costs.
Solenoid diaphragm metering pumps: Solenoid actuated, or electronic, metering pumps are a viable economical option for low flow/low pressure chemical dosing applications.