To calculate leakage in a vacuum system, you need to perform several measurements and apply a specific formula. Below is the basic procedure:
Steps to Calculate Leakage
1. System Preparation:
- Ensure the vacuum system (vacuum furnace, vacuum coating machine) is fully installed with no major gaps.
- Activate the vacuum pump to create maximum vacuum conditions.
2. Measure Initial Pressure (P1):
- Use a vacuum gauge (or system’s built-in gauge) to determine the initial pressure (P1).
- Record the initial pressure value.
3. Determine Sampling Time (t):
- Close the isolation valve between the vacuum pump and the vacuum chamber.
- The time interval (t) is measured from the moment the valve is closed until the next pressure reading (P2).
⏱️ Recommended minimum: 1 hour. The longer the time, the more accurate the leak rate.
4. Measure Pressure (P2):
- After time t, use the vacuum gauge to determine the pressure in the system (P2).
- Record this pressure value.
5. Calculate Leak Rate (L): Use the following formula:

Where:
- L = Leak rate (Pa·m³/s or mbar·l/s)
- V = Volume of the system (m³)
- P1 = Initial pressure (Pa)
- P2 = Pressure after time t (Pa)
- t = Measurement time (s)
⚠️ Notes:
- Ensure high measurement accuracy by calibrating pressure gauges and volume precisely.
- If the leak rate is high, inspect all connections and components to identify and fix leak points.
I. Choosing the Right Leak Detection Method
Based on the calculated leak rate, select a suitable detection method:🔹 Large Leaks
- Symptoms: Fast pressure drop, large gas leakage
- Recommended Method: Soap Bubble Test
→ Simple and effective for detecting large leaks

🔹 Medium & Small Leaks
- Symptoms: Slow pressure drop, minor gas leakage
- Recommended Method: Helium Leak Detector (ULVAC)
→ Detects leak rates as low as 5×10⁻¹³ Pa·m³/s, ideal for hard-to-reach areas


Image: Engineer inspecting vacuum system leakage using ULVAC helium leak detector.
II. Tips for Choosing Detection Method
- Accuracy: Choose methods with high precision to pinpoint leak locations
- Sensitivity: Use helium-based methods for detecting micro-leaks
- Safety & Convenience: Ensure the method is safe and practical for technicians
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