The total internal volume of the component or system (Liters).
Pressure at the start of the test (Bar).
Pressure at the end of the test (Bar).
Duration of the measurement phase (Seconds).
Calculation Results
Pressure Drop (ΔP):0
Leak Rate (mbar·L/s):0
Leak Rate (sccm):0
Leak Rate (mL/min):0
Annual Gas Loss (approx):0
Gas Leak Rate Calculation: Engineering Toolbox Guide
Detecting and quantifying gas leaks is a critical aspect of engineering in industries ranging from automotive manufacturing to HVAC installation and pipeline management. This Gas Leak Rate Calculator uses the **Pressure Decay Method** to determine the rate at which gas is escaping from a closed system.
What is the Pressure Decay Method?
The Pressure Decay method is one of the most common techniques for leak testing. It involves pressurizing a sealed component (the system volume) with a gas (usually dry air or nitrogen), isolating the supply, and measuring the drop in pressure over a specific period of time.
If the temperature remains constant, any drop in pressure indicates a change in the quantity of gas within the volume—in other words, a leak.
The Leak Rate Formula
The calculator employs the fundamental ideal gas law relationship derived for leak testing. The formula to calculate the leak rate ($Q$) is:
Q = (V × ΔP) / t
Where:
Q = Leak Rate (flow of gas escaping)
V = Internal Volume of the system (Liters)
ΔP = Pressure Drop (Pstart – Pend)
t = Time duration of the test (Seconds or Minutes)
Understanding the Units
Engineering leak rates are expressed in various units depending on the industry and the magnitude of the leak:
mbar·L/s (Millibar Liters per Second): A standard scientific unit for vacuum and leak testing. It represents the volume of gas (in Liters) at a pressure of 1 mbar flowing per second.
sccm (Standard Cubic Centimeters per Minute): Commonly used in mass flow controllers and industrial leak testing. It refers to a cubic centimeter of gas at standard conditions (usually 1 atm, 20°C).
mL/min (Milliliters per Minute): Roughly equivalent to sccm, often used in medical device testing and liquid handling systems.
How to Perform a Leak Rate Test
Seal the System: Ensure all ports on the part to be tested are plugged.
Pressurize: Fill the volume to the target test pressure (e.g., 2.5 Bar).
Stabilize: Allow time for the gas to settle thermally. The compression of gas generates heat; if you measure while the gas is cooling, you will get a false "leak" reading due to thermal contraction.
Test: Record the Initial Pressure ($P_1$). Wait for the Test Duration ($t$). Record the Final Pressure ($P_2$).
Calculate: Input these values into the calculator above to find the leak rate.
Factors Affecting Accuracy
Temperature: The Ideal Gas Law states $PV = nRT$. If the temperature ($T$) changes during the test, the pressure ($P$) will change even if no leak ($n$) exists. A 1°C drop in temperature can cause a significant pressure drop, mimicking a leak.
Volume Estimation: Accurate calculation requires knowing the exact internal volume of the test part and the connection hoses. An underestimated volume will result in an underestimated leak rate.
function calculateLeakRate() {
// 1. Get Input Elements
var volumeInput = document.getElementById('systemVolume');
var p1Input = document.getElementById('initialPressure');
var p2Input = document.getElementById('finalPressure');
var timeInput = document.getElementById('testDuration');
// 2. Get Input Values
var V = parseFloat(volumeInput.value);
var P1 = parseFloat(p1Input.value);
var P2 = parseFloat(p2Input.value);
var t = parseFloat(timeInput.value);
// 3. Elements for Display
var resultArea = document.getElementById('results-area');
var errorDisplay = document.getElementById('error-display');
var resDeltaP = document.getElementById('resDeltaP');
var resMbarLs = document.getElementById('resMbarLs');
var resSccm = document.getElementById('resSccm');
var resMlMin = document.getElementById('resMlMin');
var resYearly = document.getElementById('resYearly');
// Reset display
errorDisplay.style.display = 'none';
resultArea.style.display = 'none';
// 4. Validation
if (isNaN(V) || isNaN(P1) || isNaN(P2) || isNaN(t)) {
errorDisplay.innerText = "Please enter valid numeric values for all fields.";
errorDisplay.style.display = 'block';
return;
}
if (V <= 0 || t <= 0) {
errorDisplay.innerText = "Volume and Time must be greater than zero.";
errorDisplay.style.display = 'block';
return;
}
// 5. Calculation Logic
// Calculate Pressure Drop (Bar)
var deltaP_bar = P1 – P2;
// Check for pressure rise (thermal effect or sensor error)
if (deltaP_bar < 0) {
errorDisplay.innerText = "Final pressure is higher than initial pressure. Check inputs or consider thermal expansion.";
errorDisplay.style.display = 'block';
return;
}
// Convert Delta P to mbar (1 Bar = 1000 mbar)
var deltaP_mbar = deltaP_bar * 1000;
// Formula: Q (mbar*L/s) = (V (L) * DeltaP (mbar)) / t (sec)
var leakRate_mbarLs = (V * deltaP_mbar) / t;
// Convert to SCCM (Standard Cubic Centimeters per Minute)
// Standard Pressure is usually defined as 1013.25 mbar (1 atm)
// Q (sccm) = Q (mbar*L/s) * 60 (sec/min) * 1000 (cm3/L) / 1013.25 (mbar/atm)
// Simplified: 1 mbar L/s ≈ 59.2 sccm
var leakRate_sccm = (leakRate_mbarLs * 60 * 1000) / 1013.25;
// Convert to mL/min (Technically sccm is mL/min at std conditions, often treated equivalently in rough engineering)
var leakRate_mlMin = leakRate_sccm;
// Calculate yearly loss in Liters (approximate)
// mL/min * 60 min/hr * 24 hr/day * 365 day/yr / 1000 mL/L
var yearlyLoss_L = (leakRate_mlMin * 60 * 24 * 365) / 1000;
// 6. Formatting and Display
resDeltaP.innerText = deltaP_bar.toFixed(4) + " Bar";
resMbarLs.innerText = leakRate_mbarLs.toFixed(5);
// Format larger numbers with commas
resSccm.innerText = leakRate_sccm.toLocaleString('en-US', {maximumFractionDigits: 2});
resMlMin.innerText = leakRate_mlMin.toLocaleString('en-US', {maximumFractionDigits: 2});
resYearly.innerText = yearlyLoss_L.toLocaleString('en-US', {maximumFractionDigits: 1}) + " Liters";
// Show Results
resultArea.style.display = 'block';
}