Accurately calculating the injection flow rate is critical for agricultural fertigation, water treatment, and industrial chemical dosing. This calculation determines how fast a dosing pump must operate to achieve a specific Parts Per Million (PPM) concentration within a moving stream of water.
The Core Logic
The calculation relies on the relationship between the flow rate of the main water line, the concentration of the chemical stock solution, and the desired final concentration. Since stock solutions are typically much more concentrated than the target PPM, the injection rate is usually a small fraction of the main line flow.
The Formula
To find the required injection flow rate, we use the mass balance equation. The standard practical formula used in the industry is:
Note: To use this formula, the Stock Concentration must be converted from a Percentage (%) to PPM. The conversion factor is:
1% Concentration = 10,000 PPM
Input Definitions
Main Water Line Flow Rate: The volume of water passing through your system per unit of time (e.g., Gallons per Minute or Liters per Minute).
Target Concentration (PPM): The desired amount of chemical or nutrient in the final mixture. For example, 150 PPM of Nitrogen for tomato plants.
Stock Solution Concentration (%): The strength of the chemical in your supply tank. Many fertilizers or bleaches are sold as percentages (e.g., 12.5% Sodium Hypochlorite).
Calculation Example
Imagine you are treating a water system with the following parameters:
Step 3: Convert to common pump units.
0.05 GPM × 60 minutes = 3.0 Gallons Per Hour (GPH).
Applications
Hydroponics & Agriculture: Used to inject liquid fertilizers into irrigation lines at precise rates to prevent nutrient burn or deficiency.
Water Treatment (Chlorination): Determining how much chlorine bleach to inject into a well system to sanitize water without making it unsafe for consumption.
Industrial Cleaning: Mixing detergents into high-pressure water streams for cleaning machinery or vehicles.
function calculateInjectionRate() {
// 1. Get Input Values
var waterFlow = parseFloat(document.getElementById('waterFlow').value);
var flowUnit = document.getElementById('flowUnit').value;
var targetPPM = parseFloat(document.getElementById('targetPPM').value);
var stockPercent = parseFloat(document.getElementById('stockConcentration').value);
// 2. Validate Inputs
if (isNaN(waterFlow) || isNaN(targetPPM) || isNaN(stockPercent)) {
alert("Please enter valid numbers for all fields.");
return;
}
if (waterFlow <= 0 || targetPPM <= 0 || stockPercent = stockPPM) {
alert("Target PPM cannot be higher than or equal to Stock Solution PPM.");
return;
}
// Normalize Water Flow to Liters Per Minute (LPM) for internal calculation
var flowInLPM = 0;
if (flowUnit === 'GPM') {
flowInLPM = waterFlow * 3.78541;
} else if (flowUnit === 'LPM') {
flowInLPM = waterFlow;
} else if (flowUnit === 'M3H') {
flowInLPM = (waterFlow * 1000) / 60;
}
// 4. Calculate Injection Rate (Standard Dilution Formula)
// Formula: C1V1 = C2V2
// V_injection = (TargetPPM * V_water) / (StockPPM – TargetPPM)
// Note: (StockPPM – TargetPPM) accounts for the fact that the injection adds volume.
// However, in many simple calculators, they use V_inj = (Target * V_water) / Stock.
// We will use the precise mixing formula for better accuracy.
var injectionLPM = (targetPPM * flowInLPM) / (stockPPM – targetPPM);
// 5. Convert Results to various units
var finalLPH = injectionLPM * 60;
var finalGPH = finalLPH / 3.78541;
var finalMLM = injectionLPM * 1000;
// Calculate Dilution Ratio (1 : X)
// Ratio = Injection : Water
// 1 part chemical to X parts water
var ratio = (stockPPM / targetPPM) – 1;
// 6. Update UI
document.getElementById('resGPH').innerText = finalGPH.toFixed(2) + " GPH";
document.getElementById('resLPH').innerText = finalLPH.toFixed(2) + " L/hr";
document.getElementById('resMLM').innerText = finalMLM.toFixed(1) + " mL/min";
document.getElementById('resRatio').innerText = "1 : " + Math.round(ratio);
document.getElementById('results').style.display = "block";
}