Over the course of nearly two years, we’ve covered quite the range of leak detection topics – from how to use and calibrate a helium mass spectrometer to locating inert gas leaks and understanding their causes and effects. In our most recent post for this blog series, we discussed how to determine whether the furnace or the pumping system is the root cause of any vacuum-related issues.
Spray and Sniffer Probe Techniques
The spray probe technique is the traditional form of leak checking; it involves pumping down the furnace, applying helium (e.g., with a helium mass spectrometer connected) and looking for a response. The sniffer probe technique, on the other hand, is for applications where it’s not feasible to evacuate what you’re testing for leaks.
This technique involves charging, or pressurizing, a test piece with trace gas (e.g., helium). Examples of such test pieces include the heat exchanger, water-cooled flange, power feedthrough, water jackets, water-cooled fans and shafts, etc. Once the test piece is charged with the trace gas, the probe sniffs around the part for any gas that may be escaping through a leak.
When the furnace won’t pump down, we recommend writing a manual cycle that creates positive pressure within the furnace chamber. Doing so inverts the leak paths that exist. You can then use the thin film (soap bubble) method, which involves spraying a leak-detector solution on high-suspect areas; this method is normally used for gross leaks. If it starts to bubble in any areas, you know you have found a leak.
Interesting Tip: One of our Ipsen experts recommends that, in the event you do not have a professional liquid soap, do not use a dish soap/water mixture as a replacement. Instead, he recommends stopping at a department or craft store and purchasing a plastic spray bottle and children’s bubbles to use (which he claims works phenomenally as an emergency replacement).
If on the other hand, the furnace pumps down to 2,000 microns and stalls – and you have no access to a leak detector at the time – we recommend taking a spray bottle and filling it with acetone. Then have one person watch the vacuum gauge on the control system as another person walks around and lightly sprays any suspect areas.
As the acetone vapor enters the vacuum environment through a leak, the expansion of the acetone within a vacuum causes a noticeable pressure rate of rise (i.e., a spike on the vacuum gauge), which is a tell-tale sign that something you just sprayed is leaking. It is important to note that this method is generally effective at pressures of 400 to 2,000 microns.
Leak Detection: ‘Farmer’s Trick’
If you are experiencing a large leak and are in a pinch with no leak detection equipment on hand, one older trick that can be used is to take a lighter or a handheld torch and run the open flame along certain suspect areas. Such areas include: fittings, ball valves, thermocouples, thermocouple penetrations, compression fittings, small flanges, etc. If you encounter a medium- or large-sized leak while doing this, you will see the open flame bend sideways as it’s pulled by the leak.
In the end, there a number of leak detection methodologies utilized based on the situation and resources available. Here at Ipsen, though, use of a helium mass spectrometer is always the preferred method of leak checking.
Have questions about how to leak check a certain piece of equipment, or need technical assistance? We’re here to provide support. Simply call our Aftermarket Support Helpline at 1-844-Go-Ipsen (Toll Free: 1-844-464-7736; International: +1-815-332-2530) or fill out our Ask an Expert form.