Leak testing water and refrigeration circuits like water lines, water coils, on/off valves, and heat exchangers is important for product quality, function, and consumer safety. However, leak testing these circuits can be difficult due to challenges posed by their design, such as flexibility under pressure and brazed joints.
Testing can be done in a variety of ways, depending on the design of the specific parts and assemblies. Below, we discuss the different leak test technologies used for leak testing water and refrigerant circuits, and how they accommodate leak testing challenges.
Pressure Decay Testing
The simplest and most widely used technology for leak testing water circuits is pressure decay. Differential pressure decay is used for pressures above 30 psig and for testing low leak rates 0.5 to 3 scc/m, delivering a very good cycle time. Typical applications we see using pressure decay and differential pressure are leak testing components that hold or transfer fluids or shouldn’t leak water and water vapor into or out of them (such as water lines, cooling plates, water coils, valves, heat exchangers).
Helium/Tracer Gas Testing
Trace gas leak testing is used when part and ambient air temperature begins affecting pressure measurement test results. This is usually temperature related or part size related, and how a part may move based on amount of stress in the part from the pressure and how flexible the part is (part design). Tracer gas can be a good option for water coils and heat exchangers if you are experiencing size or temperature related issues.
Functional Flow Testing (Using Mass Flow)
Functional flow testing using mass flow can be done in two ways: upstream or downstream.
Upstream flow testing uses a manual set regulator flowing through a flow meter into the part, the traditional mass flow test. Traditional flow testing is highly dependent upon the regulated pressure maintaining a repeatable pressure during the entire test. If each part being tested during the process has high or low flow rates, the parts with lower flow rates will be tested closer to the manually set test pressure. Parts with high flow rates may lose some air volume faster than the manually preset regulator can supply pressure causing a lower test pressure (back pressure) to be maintained during the flow test.
To accommodate a more repeatable test pressure when these conditions occur, it is recommended to utilize a special two stage electronic regulator or flow controller in place of the manually set regulator to have a more repeatable flow test.
Downstream Flow Testing
The other reason downstream flow can be the better choice is if the part you’re measuring has holes in it. In this case, holes in the part are detected as reduced flow and measured on the downstream side. You will measure the flow leaving those holes, not as contributing to a leak.
Proof Testing or Gross Leak Testing
With a proof test, you will pressurize a part to higher-than-normal operating pressure, hold pressure constant without a major pressure loss and then measure a pressure change related to the pressure that you’re proofing your part to. Typical is 1.5-2 times working pressure.
Operator safety is a key element (making sure the part is not going to explode or injure operators). Optimally the part is inside an enclosure large enough to allow air volume to exhaust in the case of a gross leak.
Gross Leak Test
A gross leak test is similar to a proof test, however instead of holding pressure constant, a pressure decay test is conducted identifying a pressure loss over time (a gross leak test has a longer test cycle time).
Burst Testing
A burst test can be used very similar to proof testing, but the difference is that a burst test is conducted using a ramping pressure source. This technique uses a regulator with a variable flow controller or an electronic regulator. The pressure source ramps up in measured pressure increments over an identified amount of time. Instrumentation conducting a burst test will measure and identify the pressure at which the part fails, when there is a major pressure change, either through burst pressure or with the opening of a relief valve.
Sniff Leak Testing
In all of the above testing instances, if a part is identified as having a leak and rejected, sniff leak testing can be used for leak location when these reject parts are placed into a repair loop. To do this, you pull vacuum on the part and backfill with a trace gas. You then use a handheld sniff wand moving it around the part to find the exact location of the leak (CTS uses the TracerMate II instrument integrated with a mass spectrometer and integrated sniff wand or other trace gas sniffing device.
Need help with your test? Contact the leak test experts at CTS
Achieving a reliable, repeatable leak test on water and refrigeration circuits can be challenging for manufacturers. If you are having problems on your line, or would like advice setting up a new line, contact the leak test experts at CTS. We can walk you through the best test options for your application.
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