Formula used
This calculator provides three common leak interpretations.
- Pressure rise in a sealed volume:
Q = V × (ΔP/Δt), whereQis throughput in Pa·m³/s. - Direct volume change:
Qv = ΔV/Δt, giving volumetric flow in m³/s (also shown in L/s and L/min). - Mass loss with density:
ΔV = Δm/ρthenQv = ΔV/Δt, useful for liquid leaks.
For the pressure-rise method, an ideal-gas assumption is used to estimate standard flow (sccm) at 0°C and 1 atm.
How to use this calculator
- Select the method that matches your measurement setup.
- Enter the time interval for the observed change.
- Fill in the method-specific inputs (volume/pressure, ΔV, or Δm and density).
- Click Calculate to show results above the form.
- Use Download CSV or Download PDF to save your run.
Example data table
Sample runs you can replicate to validate your workflow.
| Scenario | Method | Inputs | Typical output |
|---|---|---|---|
| Vacuum chamber check | Pressure rise | V=12.5 L, P1=1.2 mbar, P2=5.6 mbar, Δt=30 s, T=293.15 K | Q ≈ 0.0183 Pa·m³/s (≈0.183 mbar·L/s) |
| Displaced air volume | Volume change | ΔV=25 mL, Δt=60 s | Qv ≈ 4.17×10⁻⁷ m³/s (≈0.000417 L/s) |
| Water drip loss | Mass loss | Δm=12.5 g, ρ=1000 kg/m³, Δt=10 min | Qv ≈ 2.08×10⁻⁸ m³/s (≈0.00125 L/min) |
1) What a leak rate represents
A leak rate describes how quickly a system gains or loses fluid through an unintended path. In vacuum work, it is often expressed as throughput, combining pressure and volume so it matches pump sizing and conductance calculations. In plumbing and process lines, volumetric flow or mass loss is easier to measure and interpret.
2) Pressure-rise testing for sealed volumes
When a chamber is isolated, a real leak produces a pressure slope over time. The calculator uses Q = V × (ΔP/Δt) after converting your inputs to SI units. This method is sensitive and fast, but it assumes the volume is rigid and the temperature is stable during the measurement window.
3) Choosing an appropriate time window
Very short intervals can be dominated by gauge noise, valve settling, or outgassing transients. Very long intervals can drift due to temperature changes or slow desorption. A practical approach is to record several windows and look for a consistent linear region, then use that region’s slope as ΔP/Δt.
4) Interpreting throughput units
Throughput in Pa·m³/s converts cleanly to mbar·L/s and Torr·L/s, which are common in leak checking. These units are helpful because they scale with chamber size: the same physical leak produces a larger pressure rise in a smaller volume. Always report the volume used in the calculation with your final number.
5) Standard flow (sccm) as a communication tool
Technicians often compare leaks using standard volumetric flow. The calculator estimates sccm using the ideal-gas relation and standard conditions (0°C, 1 atm). This is useful for comparing across different operating pressures, but it is still an estimate and depends on gas type, temperature control, and gauge accuracy.
6) Volumetric measurements when pressure is unknown
If you can capture displaced volume, use Qv = ΔV/Δt. This approach fits simple setups like bubble meters, eudiometers, or calibrated syringes. The main limitation is resolution at small leak rates, so repeated trials and longer collection times can improve repeatability without changing the physics.
7) Mass-loss testing for liquids and condensables
For liquid leaks, weighing the loss is often more reliable than measuring tiny volumes. The calculator converts mass loss to volume using ΔV = Δm/ρ. Use an appropriate density for temperature and mixture composition, and remember evaporation can mimic a leak if the container is open to air.
8) Common error sources and good practice
Outgassing, permeation, and virtual leaks can look like real leaks in pressure-rise data. Clean surfaces, bakeout, and stable temperature reduce false slopes. For any method, record instrument ranges, units, and test conditions. Exporting the results helps maintain traceability when you compare maintenance cycles or supplier parts.
FAQs
1) Which method should I choose?
Use pressure-rise for sealed vacuum volumes, volumetric for captured displacement, and mass-loss for liquids you can weigh. Pick the method that matches what you can measure reliably.
2) Why does chamber volume matter in pressure-rise tests?
For the same physical leak, a smaller volume rises in pressure faster. The throughput Q stays comparable, but ΔP/Δt changes with V, so always enter the best volume estimate.
3) My pressure decreases instead of increases. Is that possible?
Yes. Cooling, adsorption, or pump-back effects can cause negative ΔP. A negative slope usually indicates the test is not in a stable, sealed, constant-temperature condition.
4) What does sccm mean here?
sccm is standard cubic centimeters per minute. The calculator estimates it from throughput using ideal-gas relations at standard conditions, allowing easier comparison between tests and instruments.
5) Can this be used for different gases?
Throughput from pressure-rise is largely gas-independent for a given gauge reading, but converting to sccm assumes ideal behavior and standard conditions. For high accuracy, include gas properties and calibration factors.
6) How do I reduce measurement noise?
Use a stable temperature, isolate vibrations, average multiple readings, and choose a time window where the pressure trend is linear. Repeating short runs often beats one long drifting run.
7) What is a reasonable leak rate threshold?
It depends on application. High-vacuum systems may require far below 10⁻⁶ mbar·L/s, while general plumbing can tolerate much larger flows. Compare against your process limits and pump capacity.