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line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
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margin-bottom: 25px;
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function calculatePumpFlow() {
// 1. Get Input Elements
var diameterInput = document.getElementById('pipeDiameter');
var velocityInput = document.getElementById('fluidVelocity');
var diameterUnit = document.getElementById('diameterUnit').value;
var velocityUnit = document.getElementById('velocityUnit').value;
var resultsDiv = document.getElementById('results');
var errorMsg = document.getElementById('errorMsg');
// 2. Parse Values
var diameter = parseFloat(diameterInput.value);
var velocity = parseFloat(velocityInput.value);
// 3. Validation
if (isNaN(diameter) || diameter <= 0 || isNaN(velocity) || velocity 1 m³/s = 15850.3231 GPM
var flowGPM = flowM3S * 15850.3231;
// ft³/s (CFS) -> 1 m³/s = 35.3147 ft³/s
var flowCFS = flowM3S * 35.3147;
// Area in cm² for display
var areaCmSq = areaMetersSq * 10000;
// 7. Display Results
document.getElementById('resGPM').innerHTML = flowGPM.toFixed(1) + " US GPM";
document.getElementById('resM3H').innerHTML = flowM3H.toFixed(2) + " m³/h";
document.getElementById('resLPM').innerHTML = flowLPM.toFixed(1) + " L/min";
document.getElementById('resCFS').innerHTML = flowCFS.toFixed(3) + " ft³/s";
document.getElementById('resArea').innerHTML = areaCmSq.toFixed(2) + " cm²";
resultsDiv.style.display = 'block';
}
How to Calculate Pump Discharge Flow Rate
Calculating the pump discharge flow rate is a fundamental task in fluid dynamics, hydraulic engineering, and process maintenance. The flow rate ($Q$) determines how much fluid a pump moves over a specific period. Accurately determining this figure is crucial for sizing pumps correctly, ensuring system efficiency, and preventing cavitation issues.
The calculator above utilizes the Velocity-Area Method, which is one of the most common theoretical ways to determine flow rate in a closed pipe system.
The Flow Rate Formula
The basic equation for flow rate in a pipe relies on the relationship between the cross-sectional area of the pipe and the velocity of the fluid moving through it.
Q = A × v
Where:
- Q = Volumetric Flow Rate (e.g., m³/s, GPM)
- A = Cross-sectional Area of the pipe (m² or ft²)
- v = Average Velocity of the fluid (m/s or ft/s)
Step-by-Step Calculation Logic
To calculate the discharge flow rate manually, follow these steps:
1. Determine the Pipe Area
First, you must calculate the internal cross-sectional area of the discharge pipe. Since pipes are circular, we use the area of a circle formula:
A = π × (D / 2)²
Where D is the inner diameter of the pipe. If you measure the outer diameter, be sure to subtract the wall thickness twice to get the true inner diameter.
2. Determine Fluid Velocity
Velocity refers to how fast the fluid travels through the pipe. In industrial applications, discharge velocities typically range from:
- Water/General Service: 1.5 to 3.0 m/s (5 to 10 ft/s)
- Slurry/Abrasives: Higher velocities may be required to prevent settling, though this increases wear.
3. Calculate and Convert
Multiply the Area by the Velocity to get the flow rate. The result will likely be in cubic meters per second (m³/s) or cubic feet per second (ft³/s). You will typically need to convert this to more practical units like Gallons Per Minute (GPM) or Cubic Meters per Hour (m³/h).
Example Calculation
Let's say you have a discharge pipe with an inner diameter of 4 inches and the fluid velocity is estimated at 8 ft/s.
- Convert Diameter: 4 inches = 0.3333 ft. Radius = 0.1667 ft.
- Calculate Area: A = 3.14159 × (0.1667)² ≈ 0.0873 ft².
- Calculate Flow (Q): 0.0873 ft² × 8 ft/s ≈ 0.698 ft³/s.
- Convert to GPM: 1 ft³/s ≈ 448.8 GPM.
0.698 × 448.8 ≈ 313 GPM.
Why is Flow Rate Important?
Understanding the discharge flow rate is essential for calculating the Total Dynamic Head (TDH) and the Hydraulic Power required by the motor. If the flow rate is too low, the pump may overheat. If it is too high for the pipe size, friction losses will skyrocket, leading to energy inefficiency and potential pipe erosion.