The calculations below will size a chlorine feed pump in gallons per day (GPD), as if the water to be chlorinated was running all the time during a 24 hour day. When your water is actually flowing, your pump will need to feed at this rate. Whatever you determine your pump GPD output requirement to be, at least double that number to select a pump so that it will operate near midrange. This will increase your flexibility when you deal with the physical realities of your application.
Experience has developed a constant which, when multiplied by the whole number of the chlorine solution concentration (in percent) that your feed pump will be pumping, will tell you the number of gallons of water that will be treated (GT) to one part per million by one gallon of that chlorine solution. That constant is the number 10,000
If you guess at both the maximum number of gallons per minute you might need to treat, and the amount of chlorine needed, these formulas will give you a rough sizing for your pump. You might select 10 GPM and 2 PPM if you are treating a household water with no special problems. Jar testing would help you to be more precise about the actual chlorine requirement.
Example: To allow for both chlorine demand and residual, your jar testing tells you that you need to feed 2 PPM of chlorine solution. To save your clothing and minimize pump adjustments during the 30 day half life of the chlorine, you decide to dilute your sodium hypochlorite 0.5% (9 gallons of water, 1 gallon of 5.25% sodium hypochlorite). The maximum flow of water into the house may be around 10 GPM.
Notes: Doubling the output to work in midrange, you would need a feed pump with about a 12 GPD output. Please remember to select a pump model with enough pressure output to overcome any line pressure or friction losses in your system. Do you need any accessories like a solution tank or flowmeter? These formulas will work equally well if your application is commercial, industrial, or municipal. Just plug in your numbers. If your job calls for superchlorination or electronic control, or if you’d just like some help with your system, please give us a call or e-mail.