I wanted to gain a better understanding of leak testing methods so I decided to put the gloves on and have a go at leak testing myself. Under the supervision of one of our experienced engineers; I turned the leak detector on and begun my first spray test.
Set Up
The first part of the set up was to attach the test part (silver cylinder) to the helium leak detector. This can be done by taking the blank off the inlet. Once this is done, the silver pipe can be put on top of it and connected together with a swing clamp. The next step is to turn the leak detector on at the plug socket and on the LED display. It will take a few minutes to warm up.
This set up is called a hard vacuum and is needed to carry out a spray test. WIn order for a spray test to work, the air needs to be taken out of the test part and a vacuum present. To create a vacuum there needs to be less pressure within the test part. As a result, the air within the part will reduce alongside a reduction in Helium. Less pressure = greater vacuum. Therefore, having less air within the test part means that it is easier to detect if there is a helium leak.
Stages of vacuum
Middle bar: Helium leak rate reading in a bar format
Bottom bar (P Inlet): Pressure
The start button on the LED display’s home screen will begin the vacuum process and will display 3 different stages of vacuum. These stages are called Roughing, Gross and Fine (or normal on some models). Once the leak detector is switched on, the pump inside will start creating a deep vacuum. Firstly, the vacuum will start evacuating the air from the test part and this is called Roughing. Roughing is the process where the vacuum pump will go from 1000 mbar (atmospheric presssure) to 25mbar. The second stage of vacuum is the Gross stage. During this stage, the vacuum will move from 25 mbar to 5×10-1. Lastly, we have the Fine/Normal stage. This is a more refined vacuum and will stabilise around 10-3. Once a vacuum reaches fine leak mode, it will stay there as long as a vacuum is present.
The Spray Test
Credit: Pfeiffer Vacuum Website
The test part is ready for the leak test once the helium leak detector has reached the fine status of vacuum. Using a spray gun, pull down the handle and aim the nozzle at the section of the test part you would like to test. For my leak test I used the silver cylinder pictured below. The whole unit should be tested however the swing clamps and welding spots need extra attention. The test part and the coil attached should be tested. Always start with the highest point. This is because helium rises when an area is sprayed during the test.
The Results
Leak rates will show on the LED display during the leak test. Therefore, the red line on the graph represents the helium leak rate and this will peak when a leak is present. What are blue lines on graph? The blue line relates to inlet pressure and the X-axis on the graph represents different time intervals of the test.
Helium leak detectors are extremely sensitive to detecting any leaks present within a test piece. We tested this by placing a single hair follicle between 2 O rings within the top swing clamp in the test part. A gentle pull of the trigger on the spray gun sent the red line on the graph soaring. The leak created by the hair between the O rings is minute. As a result, this shows that even the smallest imperfection can picked up by helium leak detectors.
During my time at West Technology, I have mainly been in the office dealing with the admin duties. I have enjoyed my practical leak test training and find that the process itself (with a trained professional) isn’t as complicated as I originally thought. The real difficulties lie with interpreting the data and graphs. Our helium leak engineers have a wealth of knowledge and skill that takes the hassle and confusion out of leak testing. Please don’t hesitate to email us for a quote.