Chemical Feeders/ Mixers

Whether you're an industrial, municipal, commercial, or residential customer - Evoqua has the right chemical feed pump and feed pump parts for your application.

  • Solenoid diaphragm feeders can pump against high pressures (up to 600PSI) and typically include an array of automation features desirable for industrial and municipal customers.
  • Mechanial diaphragm feeders offer higher pressures (up to 300PSI), are durable, and are generally available at a lower price point compared to solenoid based feeders.
  • Peristaltic feeders use rollers to inject chemicals up to 100PSI and are ideal for residential or commercial applications of "off-gassing" chemicals like sodium hypochlorite (bleach) or sodium hydroxide as they are self-priming and do not lose prime.

Choosing a Dosing Pump

Step 1: Sizing the Dosing Pump

Properly sizing a dosing pump involves two factors - the feed rate of the chemical being dosed and the pressure that the pump will be required to pump against. For residential applications, choosing a pump that can dose chemical up to 100PSI of pressure is usally a safe bet since residential plumbing water pressures are typically in the 30-80 PSI range. Commercial or industrial dosing applications may require pumps with much higher pressure ratings. If you are unsure of the pressure that the pump is required to pump against, it is better to check first as pressures above a pumps rating can result in underdosing of chemical or even damage to the pump.

For dosing feed rate - a mathmatical formula is used to select the right pump flow rate for your chemical concentration and application. The required information for sizing a chemical feed pump includes:

  • Chemical solution concentration in PPM (parts per million)
  • Water pump (or feed flow rate) output in GPM (gallons per minutes
  • Required water concentration for application in PPM

Formula for sizing a dosing pump:

Metering Pump Output Required (in GPD) = Pump Output (in GPM) x Required Chemical Dosage (in PPM) x 1440 (minutes in a day) / Dosing Chemical Solution Strength

Determining Water Pump or Feed Flow Rate Output

Determining the flow output of your water pump or other solution to be treated depends on whether or not the system includes a water pressure tank (also called a bladder tank). If the system does not include a pressure tank, you simply need to measure the amount of water in gallons flowing divided by the time of flow. If the system uses a pressure tank to limit the on and off cycles of a pump (well or otherwise), you will need to measure the amount of water the flows from your pump only when it is running. The easiest way to achieve this is to open a valve (tap) until the pump turns on, then quickly close the valve. Measure the time the pump runs until it shuts off. Open the valve again and now measure the amount of water that flows until the pump turns on again. For example if 30 gallons of water flow between the amount of time between the pump shutting off and turning on again and it took 2 minutes for the pump to stop running when the valve was closed - your pump output is 15GPM.

Determining the Required Chemical Dosage

Determining the required dosage of chemical in PPM includes chemical absorbed by contaminants as well as the desired residual (remaining chemical after any reaction). For example, it generally takes about 1PPM of sodium hypochlorite (bleach) to oxidize each 1PPM of dissolved iron. If your water has 1PPM of dissolved iron and your residual goal is 2PPM of chlorine, then a total of 3PPM of chlorine would be required. Much more on the required dosage rate for various contaminants can be seen below under a seperate section. To some degree, when exact contaminant concentrations are not known or are variable, this can be somewhat of a trial and error type excercise. It is very helpful to have a test kit or testing meter to measure residual values of the treatment chemical when concentrations are not known.

Determining the Dosing Chemical Solution Strength

Calculating the dosing chemical solution strength is pretty straightforward - a 1% solution of chemical in water is equal to 10,000PPM. Household bleach is typically 5.25% sodium hypochlorite therefore the solution strength of household bleach is 52,500PPM. Combining one gallon of bleach with three gallons of water results in a four gallon solution of 13,125PPM. An important consideration is that many solutions, including sodium hypochlorite solutions, lose strength faster when their concentration is higher. This factor leads many dosing pumps to ususally being sized based on solutions more dilute than straight bleach. Larger chemical mixing/holding tanks should also be considered where possible.

Choosing the Actual Model of Dosing Pump - An Example

Lets assume a pump output rate of 20GPM, a required dosage of 3PPM chlorine and a dosing solution of 13,125PPM (1 gallon of bleach added to 3 gallons water). The formula becomes: 20 x 3 x 1440 / 13,125 which equals a pump with an output of 6.58 GPD (gallons per day). Choosing a dosing pump where the required output is in the middle of the range of the pump, such as a 12GPD rating pump, is wise as it allows you to adjust the dosing up or down as required.

Step 2: Dosing Pump Wet End Chemical Compatibility

The portion of a chemical dosing pump that is actually in contact with the chemical solution is called the "Wet End" of the pump. It is a simple but important exercise to identify the materials of construction of the wet end of the pump and ensure that they will not be damaged by the chemical being pumped. Most dosing pump manufacturers provide a chemical compatibility guide for various popular dosing chemicals and concentrations along with a listing of common materials used in the wet ends of their pumps. Typically each manufacturer provides several wet end material options for each pump to ensure that customers can find what they need.

Step 3: Determining Dosing Pump Controls

Manual Controlled Dosing Pumps

Chemical dosing pumps can typically be supplied with a variety of control options depending on the application. The simpliest pump controls are manual - the pump output is set using a dial or knobs and the pump is turned on and off either using a manual switch on the pump itself or by turning the power supply to the pump on and off. One of the simpliest ways to use a manually controlled pump is to wire the power for the pump in with a power switch for the well pump itself.

Externally Paced Dosing Pumps

Another type of pump is referred to as an "external pacing control" pump. Externally paced pumps utilize an signal from a dry contact flow meter or other flow monitoring device that tells the pump when to turn on and begin dosing the chemical and when to shut off. The Stenner PCM controller is a time adjustable controller that powers a fixed output pump. It operates with a pulsing dry contact water meter that sends a signal to the PCM which actuates the pump to deliver the desired dose based upon water volume. Because the Stenner PCM module controls the dosing pump by means of a standard power plug, it can be used with any brand or model of pump. More sophisticated pumps that are microprocessor controlled and are typically used for industrial applications are also available with external analog system controls (4-20mA) that allows the pump receiving the signal to actually vary the pump output based on the flow rate of the water (or treated solution).