Helium Leak Rate Calculation

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Helium Leak Rate Calculator

Calculation Results:

Leak Rate (Q): mbar·l/s

Equivalent atm·cc/s: atm·cc/s

Equivalent Pa·m³/s: Pa·m³/s

Please enter valid numeric values for all fields. Time and Volume must be greater than zero.
function calculateHeliumLeak() { var v = parseFloat(document.getElementById("systemVolume").value); var t = parseFloat(document.getElementById("testTime").value); var p1 = parseFloat(document.getElementById("initialPressure").value); var p2 = parseFloat(document.getElementById("finalPressure").value); var errorDiv = document.getElementById("errorMsg"); var resultDiv = document.getElementById("leakResults"); if (isNaN(v) || isNaN(t) || isNaN(p1) || isNaN(p2) || v <= 0 || t <= 0) { errorDiv.style.display = "block"; resultDiv.style.display = "none"; return; } errorDiv.style.display = "none"; // Formula: Q = (dP * V) / t var deltaP = Math.abs(p2 – p1); var q_mbar_l_s = (deltaP * v) / t; // Conversions // 1 mbar·l/s = 0.9869 atm·cc/s // 1 mbar·l/s = 0.1 Pa·m³/s var q_atm_cc_s = q_mbar_l_s * 0.986923; var q_pa_m3_s = q_mbar_l_s * 0.1; document.getElementById("mbarResult").innerText = q_mbar_l_s.toExponential(4); document.getElementById("atmResult").innerText = q_atm_cc_s.toExponential(4); document.getElementById("paResult").innerText = q_pa_m3_s.toExponential(4); resultDiv.style.display = "block"; }

Understanding Helium Leak Rate Calculations

Helium leak testing is a critical quality control process in industries ranging from aerospace and automotive to HVAC and semiconductor manufacturing. Because helium is an inert gas with the smallest atomic size (after hydrogen), it can penetrate even the most microscopic paths, making it the ideal tracer gas for detecting leaks.

The Fundamental Equation

The calculation for leak rate (Q) is based on the relationship between pressure changes within a known volume over a specific duration of time. The standard formula used by engineers is:

Q = (ΔP × V) / t
  • Q: Leak rate (typically in mbar·l/s)
  • ΔP: Change in pressure (Initial Pressure – Final Pressure)
  • V: Total internal volume of the test system
  • t: The time elapsed during the measurement

Why Use Helium?

Engineers prefer helium for several technical reasons:

  1. Atomic Size: Helium atoms are incredibly small, allowing them to pass through very tight leak paths.
  2. Inertness: It does not react with the materials of the component being tested.
  3. Low Ambient Concentration: Helium only exists in about 5 parts per million in the atmosphere, making it easy to distinguish "background" helium from a genuine leak.

Common Leak Rate Units and Conversions

Depending on your industry standards (ISO vs. ANSI), you may need to report leak rates in different units. Our calculator provides conversions for the three most common metrics:

Unit Standard Context
mbar·l/s European vacuum and industrial standards.
atm·cc/s Standard cubic centimeters per second (US industrial).
Pa·m³/s International System of Units (SI).

Typical Acceptance Criteria

What constitutes a "failed" test? While every application is different, here are general industry benchmarks:

  • Water Tight: 10-2 to 10-3 mbar·l/s
  • Oil Tight: 10-3 to 10-4 mbar·l/s
  • Gas Tight: 10-5 to 10-7 mbar·l/s
  • Hermetically Sealed: < 10-8 mbar·l/s (High-tech electronics/Aerospace)

Calculation Example

If you have a 5-liter vessel and you observe a pressure drop of 2 mbar over 120 seconds, the leak rate would be calculated as follows:

Q = (2 mbar × 5 Liters) / 120 seconds = 0.0833 mbar·l/s.

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