Determine system integrity using the Pressure Rise Method.
Calculation Results
Pressure Rise (ΔP):–
Leak Rate (Q):–
Equivalent in Torr·L/s:–
Equivalent in sccm (atm·cc/m):–
Equivalent in Pa·m³/s:–
Understanding Vacuum Leak Rate Calculations
In vacuum technology, determining the integrity of a vacuum chamber is crucial for process stability, pump sizing, and safety. The most common method for quantifying leaks without using a helium leak detector is the Pressure Rise Method (also known as the Rate of Rise method).
The Pressure Rise Formula
The leak rate ($Q$) is calculated based on the ideal gas law. It relates the volume of the chamber, the change in pressure over time, and the duration of the isolation test. The formula used is:
Q = (V × ΔP) / t
Where:
Q is the Leak Rate (typically in mbar·L/s).
V is the Volume of the vacuum system (Liters).
ΔP is the change in pressure ($P_{end} – P_{start}$) during the test (mbar).
t is the time duration of the test (seconds).
How to Perform the Test
Evacuate: Pump the chamber down to its base pressure or a working vacuum level.
Isolate: Close the valve connecting the pump to the chamber. This creates a closed system.
Record Start: Note the pressure ($P_{start}$) immediately after isolation and start a timer.
Wait: Allow a specific amount of time to pass (e.g., 5 minutes or 300 seconds).
Record End: Note the pressure ($P_{end}$) at the end of the duration.
Calculate: Input these values into the calculator above to find the leak rate.
Interpreting the Results
Real Leaks vs. Outgassing: It is important to note that the Pressure Rise Method measures total pressure rise, which includes both real leaks (air entering from outside) and virtual leaks (outgassing/desorption from chamber walls). To distinguish between the two, technicians often repeat the test at different pressures or after a long bake-out period.
Units conversion:
Vacuum engineering uses various units depending on the region and industry.
1 mbar·L/s ≈ 0.75 Torr·L/s.
1 mbar·L/s ≈ 59.2 sccm (Standard Cubic Centimeters per Minute).
function calculateLeakRate() {
// 1. Get Input Values
var vol = document.getElementById('chamberVolume').value;
var p1 = document.getElementById('startPressure').value;
var p2 = document.getElementById('endPressure').value;
var t = document.getElementById('testDuration').value;
// 2. Validate Inputs
if (vol === "" || p1 === "" || p2 === "" || t === "") {
alert("Please fill in all fields (Volume, Start Pressure, End Pressure, and Time).");
return;
}
var volume = parseFloat(vol);
var startP = parseFloat(p1);
var endP = parseFloat(p2);
var time = parseFloat(t);
if (volume <= 0 || time <= 0) {
alert("Volume and Time must be greater than zero.");
return;
}
if (startP < 0 || endP < 0) {
alert("Pressure values cannot be negative.");
return;
}
// Calculate Delta P
// If end pressure is lower than start pressure (pumping down), the logic implies no leak rise,
// but usually this calculator is used when isolation valve is closed and pressure rises.
// We will take absolute difference or standard rise.
var deltaP = endP – startP;
if (deltaP < 0) {
// Warn user but still calculate magnitude or set to 0?
// Usually indicates user swapped inputs or pumping continued.
// For a leak rate calculator, we assume rise.
alert("Warning: End Pressure is lower than Start Pressure. Leak rate implies pressure rise. Calculating absolute value.");
deltaP = Math.abs(deltaP);
}
// 3. Calculate Q (Leak Rate) in mbar*L/s
// Formula: Q = (V * deltaP) / t
var leakRateMbarLS = (volume * deltaP) / time;
// 4. Calculate Conversions
// 1 mbar = 0.750062 Torr
var leakRateTorrLS = leakRateMbarLS * 0.750062;
// 1 mbar*L/s = 59.2 sccm (approx) or more precisely:
// Standard condition: 1 atm = 1013.25 mbar.
// 1 sccm = 1 atm * cc / min
// 1 mbar*L/s = (1/1013.25 atm) * (1000 cc) / (1/60 min)
// = (1000 * 60) / 1013.25 sccm
// = 60000 / 1013.25 = 59.215 sccm
var leakRateSccm = leakRateMbarLS * 59.215;
// 1 mbar*L/s = 100 Pa * 0.001 m^3 / s = 0.1 Pa*m^3/s
var leakRatePaM3S = leakRateMbarLS * 0.1;
// 5. Display Results
document.getElementById('resDeltaP').innerHTML = deltaP.toFixed(4) + " mbar";
document.getElementById('resMbarLS').innerHTML = leakRateMbarLS.toExponential(3) + " mbar·L/s";
document.getElementById('resTorrLS').innerHTML = leakRateTorrLS.toExponential(3) + " Torr·L/s";
document.getElementById('resSccm').innerHTML = leakRateSccm.toExponential(3) + " sccm";
document.getElementById('resPaM3S').innerHTML = leakRatePaM3S.toExponential(3) + " Pa·m³/s";
// Show results container
document.getElementById('results').style.display = 'block';
}