Dosing and Metering Pumps
Dosing and metering pumps inject a precise, adjustable volume of chemical into a process or water stream, the standard equipment for water treatment disinfection, cooling tower chemical control, and process chemical injection. NLS sources diaphragm and piston metering pumps built to API 675 positive-displacement chemical injection pump practice, sized against the chemical, dose rate, and injection pressure a project specifies.
A dosing or metering pump doesn't move bulk flow the way a centrifugal pump does. It moves a small, precisely controlled volume per stroke, chosen because the process downstream cares more about exact dose accuracy than about flow rate. A diaphragm flexes back and forth, or a piston strokes in and out, drawing in a fixed volume of chemical and pushing it out through a check valve on each cycle, which is what makes the output repeatable and adjustable down to a fraction of a liter per hour.
NLS sources both diaphragm and piston metering pump designs. Diaphragm metering pumps handle most chemical dosing duty, since the diaphragm keeps the chemical fully isolated from the drive mechanism, important for aggressive chemicals like sodium hypochlorite or acid where any leak path is a hazard. Piston metering pumps suit higher-pressure injection points, where the process line pressure the pump has to inject against runs high enough that a diaphragm design loses accuracy. Stroke length and stroke frequency together set the dose rate, and most units on the market give an adjustable range wide enough to cover a process's normal turndown without changing pump heads.
On Saudi projects, dosing pumps show up on water treatment plants for chlorine, sodium hypochlorite, or coagulant dosing, cooling tower systems for biocide and scale-inhibitor injection, and process lines needing pH correction or corrosion inhibitor injection. NLS references API 675 as the applicable positive-displacement chemical injection pump standard for process and utility applications, covering the reliability and accuracy expectations these systems run to.
NLS quotes dosing pumps against the chemical being dosed (concentration and compatibility with wetted materials), the required dose rate range, and the injection point's back pressure. Wetted parts, PVC, PVDF, or stainless steel depending on the chemical's corrosivity, and the diaphragm or seal material drive both price and compatibility, so NLS confirms the chemical data sheet before quoting rather than defaulting to a generic wetted-parts assumption that may fail against the actual fluid.
Specifications
- ✓Configuration: diaphragm metering pump and piston metering pump
- ✓Standard referenced: API 675 positive-displacement chemical injection pump practice
- ✓Wetted material options: PVC, PVDF, and stainless steel depending on chemical compatibility
- ✓Dose control: adjustable stroke length and stroke frequency for turndown without changing pump heads
- ✓Sizing basis: chemical concentration and compatibility, required dose rate range, injection point back pressure
- ✓Typical use: water treatment disinfection dosing, cooling tower chemical control, process pH and corrosion-inhibitor injection
Frequently Asked Questions
What's the difference between a diaphragm and a piston metering pump?+
A diaphragm metering pump keeps the chemical fully isolated from the drive mechanism, the safer choice for aggressive chemicals like sodium hypochlorite or acid. A piston metering pump handles higher injection pressures more accurately, used where the process line pressure is too high for a diaphragm design to hold dose accuracy.
How does NLS determine the right wetted material for a dosing pump?+
Against the chemical's compatibility data, PVC and PVDF suit most acids and hypochlorite solutions, while stainless steel is chosen where the chemical or the process temperature rules plastics out. NLS asks for the chemical data sheet before quoting rather than assuming a default material.
Can a dosing pump's output be adjusted after installation?+
Yes. Stroke length and stroke frequency are both adjustable on standard metering pumps, giving a dose rate range wide enough to cover normal process turndown without swapping the pump head, which is one reason these pumps are specified for variable dosing duty rather than a fixed-output pump.