In a time of tight budgets, no utility can afford to waste chemicals. A new chemical metering pump from Watson-Marlow Pumps Group is designed to enhance metering accuracy for applications like disinfection, pH adjustment and flocculation in drinking water, wastewater and industrial process water treatment systems.

The Qdos 60 peristaltic metering pump, along with the previously introduced Qdos 30 model, extends the capacity range of the company’s peristaltic pump line to incorporate flows from 0.001 to 15 gallons per hour. The Qdos 60 is best suited for larger treatment plants.

The pump is designed to cut chemical waste with accurate, linear and repeatable metering. The manufacturer says it helps reduce chemical costs even when metering difficult fluids or when pressure, viscosity and solids content vary.

Peristaltic technology enables precise, continuous, smooth flow for optimal fluid mixing. The pump needs no ancillaries and is simple to install and maintain. Russell Merritt, marketing manager with Watson-Marlow, described the technology to Treatment Plant Operator.

TPO: What did you observe that water and wastewater customers were looking for in chemical metering pumps?

Merritt: Customers were asking for a metering pump with a relatively low cost that would be highly accurate, be able to maintain its accuracy over varying process conditions and be simple and inexpensive to maintain. We designed the Qdos 60 as a drop-in replacement unit that comes with our expertise in building fundamentally robust peristaltic pumps.

TPO: Why is this pump model especially suited for water and wastewater applications?

Merritt: It’s a good choice partly because of its peristaltic technology, which has been proven extraordinarily accurate for metering. It offers in a very small footprint a pump capable of metering chemicals against the high pressures common in the environmental market, typically up to about 100 psi. It also delivers chemicals such as ferric chloride and caustic that are very aggressive in nature, while containing them within the pumping mechanism, so that when maintenance has to happen, operators aren’t at risk of being exposed.

TPO: How do operators control the output of the pump?

Merritt: We combined the pump with a display that provides a lot of control flexibility. It is a 3.5-inch thin film transistor full-color display, which has excellent contrast in varying light conditions. Operators can easily see data such as flow rate, speed, current input and alarm status. It’s a straight push-button interface and requires a minimal number of key presses. The keys are large enough so operators wearing gloves can still operate it easily. The system has advanced control features that include fluid level monitoring, fluid recovery, line priming and intuitive flow calibration.

TPO: In simple terms, how does a peristaltic pump work?

Merritt: In concept it is very similar to the way the esophagus works in our bodies. A rhythmic compression-decompression motion moves the product forward. The pump has a tube contained inside a pump header that has a rotor pressing on it at two pinch points. It draws a vacuum that pulls product in on one side and it rotates to push product out on the other side.

TPO: Why is this method of pumping highly accurate?

Merritt: A peristaltic pump is not subject to inaccuracies that result from varying pressure conditions. As a positive displacement pump, it will always put out the same amount of product per revolution, regardless of the pressure on the discharge side, and regardless whether the inlet conditions change. So even if pulling from a tank where the level may change, the pump will still be accurate. And if the product is likely to produce gas, as with sodium hypochlorite, the pump will not lose its accuracy, nor will it vapor lock and fail.

TPO: How does this type of pump help utilities save on chemicals?

Merritt: The calibration does not change with variation in discharge or duty conditions. If that were to happen, operators could find themselves discharging more chemical than needed, or potentially less, which would create a worst-case scenario where treatment is not up to standards and corrections would have to be made. The lack of wastage, and the fact that operators know they’re metering and dispensing the exact amount of chemical needed at all times, will definitely save utilities money.

TPO: What does maintenance on this pump model include?

Merritt: Maintenance is incredibly simple. A pump can be fully rebuilt in less than one minute, and that is a boon for any facility that has multiple metering pumps. In a peristaltic pump, the tube inside the pump head is the only wearing part – nothing else inside the pump mechanism actually contacts the product.

When the tubing fatigues, the control system will alarm the pump and tell the operator that the pump head needs to be replaced. The operator simply removes what we call the ReNu pump head – there is no need for special tools. He puts on a new pump head and re-enables it, and it’s ready to go. There are no seals and diaphragms to change out and there are no ancillaries like backpressure valves, degassing valves or pulsation dampeners.

The ReNu pump head, which is essentially the entirety of the pump, is a very simple spare part to deal with. It doesn’t require any specialized training to install.

TPO: What is involved in retrofitting this pump to an existing pump installation?

Merritt: That is also simple. The pump is similar in footprint and general size to any of the other metering pumps on the market. The interface is accomplished through standard quick-disconnect fittings, so connecting it to existing piping is also very straightforward.