Experiment 7

Rate-of-Rise Experiment

 

Objective: Develop skill in the rate-of-rise method of leak detection.

Reference: Modules 13

Required Materials:

Varian Vacuum Trainer

Stopwatch

Latex gloves

 

Experimental Procedure:

1. The vacuum system must be at base pressure with the ion gauge operational. Refer to Experiment 3.

2. Record the base pressure.

3. Close the high-vacuum valve and start the stopwatch.

4. Record the time and pressure every 30 seconds for the first 5 minutes, then every minute for the next 5 minutes, and every 5 minutes until a minimum of 3 decades of pressure data are collected.

5. Plot pressure versus time on log-log paper.

6. Open the high-vacuum valve and allow the system to reestablish base pressure.

7. Adjust the leak valve until pressure rises a factor of two, i.e. until the pressure doubles.

8. Close the high-vacuum valve and start the stopwatch.

9. Record the time and pressure every 30 seconds for the first five minutes, then every minute for the next five minutes, and every five minutes until a minimum of three decades of pressure data are collected.

10. Plot the data and compare the graph obtained in Step 9 with the graph obtained in Step 5.

11. Observe the slopes of the two curves for leak size indication, Q = V dp/dt