Browsing the “Chemical Feed” section, you’ll find over 100 pages devoted to various types and sizes of chemical feed pumps and accessories. With red, yellow, blue and gray pumps, expensive and relatively inexpensive pumps – how does one sort through these choices to determine the best application match? Start by asking these questions:
What chemical?
The first step is determined by your choice of chemical. You will find an indicator next to most feed pumps in our book designating the chemical that the model is intended for. Check with USABlueBook Technical Support Department to confirm compatability.
Diaphragm or peristaltic pump?
Diaphragm pumps are satisfactory for feeding most water and wastewater treatment chemicals, except for two problems. One is that they can only achieve a maximum suction lift of about 5 feet, and even less for viscous liquids. If the installation requires higher suction, peristaltic pumps are capable of up to 20-ft lift.
The other problem is that, when feeding hypochlorite, a gas is formed that can “air bind” diaphragm pump feed lines. Pumps designated for chlorine service include a “de-gassing” valve that will normally alleviate air binding if the pump is operating above 3 gpd. If the required feed rate is less, dilute the hypochlorite and operate at a higher feed rate. An alternative is to use a peristaltic pump that is not subject to air binding.
Peristaltic pumps also have the advantage of being able to feed almost any liquid, even if it is somewhat abrasive. The down side of peristaltic pumps is that the “squeeze tube” will normally only last a few months and must be periodically replaced.
Is the pump to be automatically paced?
If the feed rate of your chemical feed pump is to be automatically varied in response to a signal from a meter or controller, select a model that is equipped for a 4-20 mA input. On the other hand, you may be using the feed pump where the feed rate is relatively fixed. An example would be adding a chlorine residual to well water. The water’s chlorine demand is usually stable and the well pump output is constant. A relatively simple feed pump can be used to dose at a fixed rate whenever the well pump is operating.
How variable is the feed rate?
The least expensive diaphragm feed pumps only have a variable setting for stroke — in other words, the amount of chemical pumped on each stroke. Although the stroke adjustment has a setting range of 0 to 10, it’s best to operate within 3 to 8. For relatively fixed feed rates, a pump of this type will work fine. But, if there is any chance that your feed rate requirement will vary over a wider range, it is preferable to control both stroke frequency and length. This provides a wider range of control.
Pump capacity and pressure?
Select a pump with capacity slightly larger than the anticipated capacity. Remember, running the pump wide open for extended periods of time isn’t a great idea! Also consider the water pressure of the pipe that is being fed. The pump should be rated for at least 20 psi over the line pressure.
What’s your price range?
All of the chem feed pumps we sell are industrial-grade and rated for water and wastewater system use. But if your budget will allow, consider opting for some of the special features found on the slightly more expensive pumps. Those options may save you time and money in the long run.
