2903 W. Whitton Ave, Phoenix, AZ 85017
P.O. Box 27296, Phoenix, AZ 85061-7296
602 650-1557 / 800 443-6936


Liquid Chlorination System Sizing


The selection of a chlorine solution metering pump is dependent upon the flow rate of the water to be treated, in gallons per minute (GPM); the chlorine demand of the water, in parts per million (PPM); and the concentration of the chlorine (Cl2) solution, in percent (%). The feed rate of the metering pump is expressed in gallons per hour (GPH).

Chlorine demand is the tendency of the water you are treating to consume the chlorine that you inject into the water. Chlorine demand in your water is affected by many different things. Some of them may be: algae, bacteria, iron, manganese, hydrogen sulfide, water temperature, and agitation or aeration of the water. While it is possible to test for chlorine demand, experience has shown the following values to be very reliable for estimating chlorine demand:

  • Well Water - 1 to 2 PPM
  • Surface Water - 4 to 5 PPM
  • Wastewater - 8 to 10 PPM
Calculating Chemical Feed Rate
Process flow rate (GPM) X
Dosage (PPM) X 60 minutes/hour
Chemical Feed Rate (GPH)
Solution Strength (%)  

The above formula will calculate the GPH metering pump rate required based on a GPM flow to be treated at a specific PPM dosage based on the percent concentration of the chemical being pumped.

Adjusting Metering Pump with Stoke Length and Stroke Speed Control
Desired GPH Output
Pump Maximum GPH Rating
% Setting Stroke Length
% Setting on Speed Dial

The above formula will tell you where to set the mechanical stroke length and stroke speed controls based on the maximum pump capacity and the desired GPH pump rate. If you select a stroke length, it will give a stroke speed. Adjust stroke length to get varying stroke speed results.

Adjusting Metering Pump with Stoke Length Control Only
Pump Maximum GPH Rating
Desired GPH Output
% Setting on Dial

The above formula will tell you where to set the stroke length adjustment, on a pump that has just stroke length control, based on the maximum pump capacity and the desired GPH pump rate.

Dilution of Chemical Solutions
Starting Concentration - %
Final Diluted Concentration - %
Gallons of concentrated solution
Gallons of Dilution water to add/gallon of Starting Solution
Total Gallons of Dilute Solution Produced
The above formula will tell you how many gallons of water to add to a concentrated solution to create a diluted solution for feeding. Use this calculator to determine the dillution of a high concentration chlorine solution to a lower more stable chlorine solution.

System Backpressure:

In addition to determining the metering pump feed rate, in GPH, you also need to know the system "backpressure." The backpressure. is the pressure at the point the metering pump will be injecting the chlorine solution. All metering pumps are rated to provide some maximum GPH at a maximum PSI backpressure. If you exceed the backpressure. rating of the pump it will either not pump as much as it is rated for, or it may not pump at all.

Calcium Carbonate:

If you are using hypochlorite for chlorination, and you have hard water, you will notice calcium carbonate buildup. If you use hard water to make your hypochlorite solution you will notice a white precipitate in the chlorine solution tank. If you are injecting hypochlorite into hard water you will find calcium carbonate accumulating on the injection diffuser, where it injects into the main line. This precipitation of calcium carbonate is caused by the high pH of the hypochlorite solution. Calcium carbonate can easily be removed by dropping the calcium carbonate covered parts in an acid solution. Once the bubbling stops, they are clean!


To make a complete chlorination system, you may need to add the following accessories to the metering pump that you select:

Chlorine Solution Tank:

Typically this is a 50 gallon polyethylene tank with a molded cover. The molded cover allows mounting of the metering pump and a mechanical mixer and also has openings for adding water and hypochlorite. Other sizes and materials are available on special request.

Mechanical Mixer:

When you are using calcium hypochlorite to make your chlorine solution, you need to have a mechanical mixer to provide agitation to dissolve the powder. For the typical 50 gallon solution tank this is done with a 1/20th H.P. 1750 RPM mechanical mixer. The mixer has a stainless steel impeller and shaft with a special epoxy coating to protect the stainless steel from the chlorine solution.

Chlorine Residual Test Kit:

Once you have your system installed and running, you need to take periodic chlorine residual tests to confirm that the pump is properly adjusting and also operating properly. A DPD chlorine residual test kit is the accepted test method for this procedure. Refer to Chlorine Residual Testing section.


There are two sources of chlorine solution available, sodium hypochlorite (bleach) and calcium hypochlorite (powdered chlorine).

While you can purchase 5 ¼% sodium hypochlorite (bleach) at the market, or calcium hypochlorite (powdered or tablet chlorine) at the hardware store, these products are not NSF approved.  For potable water applications in Arizona all chemicals must be NSF 60 approved.  For NSF 60 approved chemicals you will need to contact a supplier such as Hill Brothers Chemical or Univar.

Chlorine solution concentrations greater than 2-3% have a tendency to be unstable. When this happens the concentration of the chlorine solution will decline over time. If the strength of your chlorine solution changes, then you will need to keep adjusting the metering pump feed rate to maintain a constant residual.

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