Leakage Rate Calculation

Leakage Rate Calculator (Pressure Decay)

Calculated Results:

Leak Rate: mbar·L/s

Equivalent to sccs (Standard cm³/s)

Total Pressure Drop: mbar

function calculateLeakRate() { var volume = parseFloat(document.getElementById("testVolume").value); var time = parseFloat(document.getElementById("testTime").value); var startP = parseFloat(document.getElementById("startPressure").value); var endP = parseFloat(document.getElementById("endPressure").value); var resultArea = document.getElementById("resultArea"); if (isNaN(volume) || isNaN(time) || isNaN(startP) || isNaN(endP) || time <= 0) { alert("Please enter valid positive numbers for all fields."); return; } var deltaP = startP – endP; if (deltaP < 0) { alert("Final pressure cannot be higher than initial pressure in a decay test."); return; } // Formula: Q = (V * deltaP) / t var leakRate = (volume * deltaP) / time; // 1 mbar·L/s is roughly equal to 1 sccs (standard cubic centimeter per second) // at standard atmospheric conditions for simple conversions. var sccs = leakRate * 1; document.getElementById("leakRateResult").innerText = leakRate.toFixed(6); document.getElementById("sccsResult").innerText = sccs.toFixed(6); document.getElementById("dropResult").innerText = deltaP.toFixed(4); resultArea.style.display = "block"; }

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Understanding Leakage Rate Calculation

In industrial engineering and quality control, calculating the leakage rate is vital for ensuring the integrity of hermetic seals, automotive components, medical devices, and HVAC systems. The most common method used is the Pressure Decay Test.

The Pressure Decay Formula

The leakage rate (Q) is determined by monitoring the change in pressure over a specific period within a known volume. The fundamental physics formula is:

Q = (V × ΔP) / t

• Q: Leakage Rate (typically measured in mbar·L/s)
• V: Internal Volume of the test object (Liters)
• ΔP: Pressure Drop (Initial Pressure – Final Pressure)
• t: Test Duration (Seconds)

Common Industry Units

Depending on the industry and the sensitivity required, leak rates are expressed in various units:

Unit	Description
mbar·L/s	Millibar-Liters per second (Standard European)
sccs	Standard Cubic Centimeters per Second
Pa·m³/s	Pascal-Cubic Meters per second (SI unit)

Practical Example

Imagine you are testing an automotive fuel tank with an internal volume of 5 Liters. You pressurize it to 1000 mbar. After 30 seconds, the pressure drops to 998 mbar.

1. Volume (V): 5 L
2. ΔP: 1000 – 998 = 2 mbar
3. Time (t): 30 s
4. Calculation: (5 × 2) / 30 = 0.333 mbar·L/s

If your quality standard requires a leak rate of less than 0.1 mbar·L/s, this part would be considered a failure.

Why Factors Like Temperature Matter

When performing precision leakage rate calculations, environmental factors play a huge role. According to the Ideal Gas Law (PV=nRT), a change in temperature will cause a change in pressure even if there is no physical hole in the part. If the test medium (air) cools down during the test, the pressure will drop, resulting in a "false leak" reading. Professional leak test machines often include temperature compensation algorithms to mitigate this effect.