Precision Plus Technical Articles
TECH ARTICLE OF THE MONTH
Detecting & Repairing Vacuum Pump Leaks
A leak in your vacuum system can cause unwanted pressure changes as well as damage to the system by allowing air in or gases out; both of which can result in a solid formation, or explosion.
Protect your system by learning where leaks can appear, what methods you can use to detect them, and how to further prevent leaks from occurring in the future.
What exactly is a Vacuum Leak?
A vacuum leak causes pressure changes resulting from a hole between atmosphere and the vacuum interior. It can also result from the progression of gas and vapors within the system. Leak sources include:
• Vapors – given off by the process load
• Trapped Volumes – pockets of gas released from within the system
• Outgassing – from internal surfaces
Why Test my vacuum system?
Everything leaks! And it is probable that your system will at some point in time. Test monthly to:
• Assure ultimate pressure
• Prevent air from entering the system
· Process gases reacting with oxygen can lead to solid formation or
explosion
· Process gases reacting with water vapor can lead to solid formation
• Prevent process gases from escaping the system
What methods can I use to Detect leaks?
There are many methods you can use to detect leaks. Click on a method below for more information on some of the more popular forms of leak detection.
• Pressure Rise
• Masking
• Bubble Testing
• Spark Testing
• Halide Torch
• Discharge Tube
• Thermal Conductor
• Pirani Leak Detector
• Dye Penetration
• Helium Mass Spectrometer
What are the most Common Areas of vacuum leaks?
The most common areas of vacuum leaks are those in which connections are made during assembly, including but not limited to:
• O-Ring applications
• Areas with welds
• Turned parts
• Bolts placed in blind holes
If I find a leak: Is there an acceptable leak Rate at which I can still run my system?
An acceptable leak rate is relative to your ultimate pressure. If your system can still achieve ultimate pressure with minimal leakage, you may be able to get by. Although, in these cases, leaks may not even be detectable.
The minimum detectable leak is 10-12 cc/s.If you are able to detect a leak, you should make every effort to repair it. Leak rate can change at the drop of a hat and is particularly influenced by:
• Gas Density – lighter gases pass through holes faster than air
• Gas Temperature – gas molecules move faster in higher temperature
applications
• External Pressure – is it atmosphere (760 torr)? Higher external pressure will
increase leak rate.
Know that any leak is a bad one and can ultimately damage your system. If you detect a leak, it is best to find the source and fix it as soon as possible for optimal performance.
How do I Repair a leak once I find it?
Check your fittings and connections! You may need to simply reassemble that part of your system or replace a spare. More serious leaks may require the repositioning or replacement of a weld.
TIP: Be sure to perform an additional leak test after your repair!It pays to check your work. Plus there could be other leaks in surrounding areas that you may have passed over or that popped up during your repair.
How do I Prevent a leak from occurring or reoccurring?
Know and take care of your system! A pump operator should be familiar with the ins and outs of his/her system, including how it is assembled. If you are unfamiliar with how your pump was built and its components, be sure that you know of someone who is familiar that you can easily reach for assistance.
Also, be sure to purchase the highest quality parts available to you. Better parts make for a better pump.
TIP: Keeping a copy of your pump schematic on hand helps!
DID YOU KNOW? Precision Plus has pump schematics online! Download and print a copy for a quick reference. It’s FREE!