It’s true that this is a rare instance however, as vacuum pressures drop and lower even the most solid and safe of systems will soon reveal that they are not secure. The tightness (or “the lack of the presence of leaks”) is essential for a variety of reasons, such as maintaining and ensuring the pressure and vacuum and safety of the product as well as environmental standards and to improve the efficiency of processes. There are two elements of leak technology that are worth looking into for leak detection as well as leak measurement.

LEAK DETECTION

Different vacuum techniques and applications have different leak rate specifications. What is considered acceptable at a lower level is deemed to be completely unacceptable (and definitely extremely dangerous) at an elevated vacuum. The only reliable method to identify leaks less than 1×10-6 mbar*l/s is to use a leak detector for helium. The leak diameter of 1×10-12 mbar*l/s (which corresponds to one atom) can also be the size of a helium-containing molecule and is the lowest leak rate that can be identified.

What is the reason for HELIUM employed to detect leaks?

Helium is an indicator gas to identify leaks, and this is due to several reasons. This is due to the fact that it only makes up 5 ppm of air meaning that the background levels are extremely low. Helium is also relatively small in mass which makes it “mobile” and inert and non-reactive. Helium is also not flammable and generally inexpensive.

Helium’s association with it is one of the primary reasons for the fact that some of the most precise and efficient leak detection techniques utilizes helium as the tracer gas, as well as mass spectrometers for analysis and measurement. Additionally, helium is selected to be a tracer gas since it is extremely light, rapid and totally non-toxic.

Helium Leak Detection

Helium detection is carried out by following a method The unit that is being inspected is either pumped from within or pressured from outside using the helium. The gas that is released from potential leaks is collected and then pumped through the mass-spectrometer to be used for studying, and any measurement that is higher than that of the apparent trace of Helium can be an indication of leakage. The spectrometer works the following manner: any Helium molecules that are absorbed by the detector will be ionized and the helium ions eventually “fly” to the trap. There, the Ion current is studied and recorded. Based on the ionization rate, the leak rate will be determined.

Reference (or background) reading of the helium element is an essential aspect that is essential to the entire process. This reading gives an indication of the “background sound” for helium. This is thought of as the level that is acoustic to the gas. The bulk of this background helium is found in between 100-150 micro-layers of gas molecules. It is a permanent gas (contained within the air) which is found in devices for leak detection, pump or test components. The process of getting rid of the helium on the surface is known as “degassing” and it begins after all it has been removed and the molecules are “desorbing” from the layer of the metallic. The desorption process begins at around 10-1 mbar. Degassing that occurs by lowering the pressure or heating the chamber’s surface is not unusual; however, it is not enough to entirely eliminate the gas that is present on the surface. Apart from surface Helium “standby” the gas is found in O-rings that behave as sponges, while also giving an indicator of the cleanliness of the unit. Modern leak detectors for helium are able to continuously determine and measure the inner (background) level, and then automatically subtract it in the calculation of leak-rate.

LEAK MEASUREMENT

In order to determine the leak rate of gasses Pressure plays a significant part in determining the magnitude of a leak). A leak’s rate represents the volume of gas that is able to flow through the membrane at a certain pressure differential over a period of. The basis for leak rate calculations is: the leak’s diameter is circular and the leak channel’s diameter is comparable to the size of the substance that it “passes” over. Rate of leak = gas quantity/time (pressure x time) and is expressed in mbar*l/s , or equivalent units.

LEAK METHODS FOR DETECTION

There are many leak detection methods. The one you use is largely determined by the vacuum or pressure under test. The most straightforward is the test of bubbles, most effectively demonstrated by using a punctured bicycle pump under water and tracing the location where the bubbles are or by placing the washing-up liquid over the junction of an active water/gas pipe and then observing if the liquid produces the appearance of a froth. Both are reliable methods of discovering leaks of low pressure. The bubble test is used for vacuums up to 10-4 mbar.

The test for pressure decay is precisely that chamber is pressurised and the drop in pressure is recorded and observed. The test for pressure decay is performed up to 10-3mbar. The test of pressure rise operates in reverse. The chamber’s pressure is raised, and the ability to keep pressure constant is measured against the pressure reading at the inlet. The test for pressure rise is performed up to 10-6 mbar*l/s.

But, it’s the”integral” mode and the “integral” modes (accurate of 10-12 mbar*l/s) and the”sniffer” test with helium “sniffer” test (accurate between 10-7mbar*l/s) and are the most demanding leak detection methods in high vacuum levels.

HOW TO HELIUM DETECTORS WORK?

Four Helium Leak Methods for Detection (HLD) methods

There are two types of helium leak-detection (HLD) methods either through integral testing or local testing. The method to employ is dependent on the specific situation, and also on what the final product is intended to be employed for. “Internal” or “integral” method determines whether there is a leak (but it does not show how many leaks) The “local” method identifies the location of leaks (but the precise determination of the leak size or rate can be difficult). Both detection methods are able to be subdivided into two additional components: “sample under pressure””sample under vacuum” and “sample in vacuum”.

The first of two procedures for testing that are integral is known as”the “integral (sample under pressure)” method. This involves the chamber of the test being sealed in a container. The chamber is then filled using helium as well as the container then connected with the leak detection. If there is leaks, a small amount of gas inside the container is taken and then passed through a mass-spectrometer. There, any rise (over what is recorded in the background) in the levels of helium is recorded.

When using the “integral tests (sample within a pressure)” method the chamber is placed inside a container however the container is pressure-filled by helium as well as the chamber that is attached to the leak detector. A small amount of the gas inside the chamber is then drawn out and then passed through a mass spectrometer . There there is an increase in the helium content from an initial reading will be recorded.

The second set of tests are often called the “sniffer” or “spraying” test. When using”sniffer” or “local-sniffer (sample at the pressure)” method chamber, it is pumped up using helium, along with a sniffer apparatus is positioned over the potential leak point (welds and flanges instruments ducts, etc.) to trap any gas that escapes. The “sniffed” gas then gets then passed to a mass-spectrometer to monitor anything that is elevated (i.e. above background) helium levels.

The “local-spraying (sample beneath vacuum)” method the chamber is to be pumped, and the it is then sprayed towards leaky points in the hopes that some of the pure helium be drawn inside the chamber. The gas that is released from this chamber is then pumped through a spectrometer in order to measure any elevated levels of helium.

To summarize and simplify the distinctions between these two HLD types The integral method requires that the chamber be set inside a gas-proof enclosure (not necessarily a requirement but a possibility) while using the local test method, the chamber can be internally pressurised using helium or vacuumed using helium that is generously sprinkled on the chamber’s surface at leak-prone areas. In both cases the leak detector via potential leaks before being transferred through the spectrometer to analyse.

HELIUM Standard LEAK RATE

There are various standards that relate to leak detection and detectors for leaks. One of them, the DIN EN1330-8 standard, specifies the standard leak rate for helium to be used when a leak test is carried out using the use of helium with a differential pressure of 1 bar between atmospheric pressure to less than 1 Mbar internal pressure (which is in reality the norm under these circumstances).

Which is the SI unit for leakage rate?

The SI unit for the leak rate measured is Pa.m3.s-1. The SI unit for pressure is Pascal (Pa) in which 100 Pa equals 1 mbar, which is 1 hPa. A common unit used to measure leakage rate would be mbar.

What is the leak rate measurement?

The leak rate test is used to measure the amount of air that is leaking into the chamber. The leak rate that is acceptable is determined by the requirements of the application.

Standards for safety and environmental protection demand that manufacturers ensure the tightness of their products by conducting leak tests as part the process of quality and production approval. To determine the rate of rejection of a test conducted that uses helium in the standard conditions of helium It is required to convert the test conditions to helium normal conditions. There are standard formulae for these conversions.

If a vacuum system has been connected with a leak detector normal helium conditions should be in place for leak detection. Utilizing helium for leak tests ensures consistent and reliable results that are quantifiable and monitored continuously.

THE HELIUM CHALLENGE

It is important to recognize that there are some difficulties in detecting tiny leaks with the helium. HLDs are extremely sensitive, and helium that is entrapped or surrounding it could affect the accuracy of leak detection and measurement. A leak detector is not a leak-proof device and that’s why having a clean helium environment is crucial if accurate readings are expected. Furthermore, in the case of tiny leaks, it’s crucial to be aware of external influences because they can affect the results. Additionally, helium from the outside can be introduced into the system through venting and exhaust ports and also permeate through O-rings.

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