We build leak test stations


We design and build dedicated machines for leak testing of containers, components, parts. Our projects mostly use leak testers of ATEQ brand, such as F570, F52000 and also F405, F580, C540. We boast robotic leak testing machines .

Designing leak testing machines, our designers have practical knowledge of various leak testing methods. This enables them to customize the machines according to clients’ requirements. The most common requirement of customers is to reduce the testing time. Unitem company for such need uses special sockets often with vision system . This allows to reduce testing time even up to 80%!

There are no perfectly tight objects, however, it is possible to achieve very high tightness degree defined by safety standards (which is especially important in devices using explosive or toxic gases) or product standards defined by constructors to fulfill its function. We can design, and build leak detection testers to the standard you specify.

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There is no such thing as a perfectly tight object, but it is possible to achieve a very high degree of tightness as defined by safety standards (which is particularly important in equipment that uses explosive or toxic gases) or by product standards set by the constructors in order for it to fulfil its function. We are able to design, and build leak testers that detect leaks according to the standard specified in the order.

Below we present an industrial machine for gearbox cover tightness testing including channel patency test. On our website, you can find description and application of tightness testing methods which we use in assembly machines and inspection stations we build.

Leakage is a feature of every tank (chamber), whether it is a windshield washer fluid tank or a high-vacuum apparatus used in the semiconductor industry. However, from the point of view of applications, it is important to answer the question what is the acceptable leakage value at which the tank continues to perform its intended functions. Below this value, we define the level of rejection of defective products. Leakage belongs to that category of concepts whose measure is always greater than zero.

There are three types of leakage:

  • real , apparent and resulting from gas permeation through the walls of the tank (chamber). Actual leaks relate to the presence of holes, gaps or channels connecting areas of different pressures and allowing gas to flow between these areas. Such leaks occur most often in the vicinity of connections and are usually the result of design, technological or assembly errors, and in a few cases – hidden material defects.
  • apparent are related to the presence of adsorbed gases on the inner walls of the tank (chamber), gases trapped in the micropores, residual lubricants, solvents and other organic pollutants. The apparent leaks play an important role in the technique of high vacuum (and higher – pressure below ~ 10 -3 mbar), i.e. in technologies requiring high purity of the process (e.g. metal vapor deposition).
  • resulting from gas permeation through the walls of the tank can generally be neglected due to the choice of technology.

In the art, the leak rate is often given in terms of the gas flow rate. The most commonly used units are: [W = Pa · m 3 / s], [mbar · l / s], [mol / s], and [Tr · l / s].

Leak detection methods can be divided into vacuum and pressure methods depending on whether the gas pressure inside the test object is lower or higher than the atmospheric pressure.

Some of these methods allow you to locate the leak, others only measure the resultant leak rate.

The lowest leak rate detected by a method determines the sensitivity of the method.

Unitem uses the following methods in leak test stands:


Thermal imaging method of component tightness testing

The most popular pressure leak test method used in the automotive industry is the method of slow pressure changes. A significant limitation of this method is the lack of indication of the leak location. Another disadvantage is the very long measurement times (at least several dozen seconds) for details that undergo significant deformation under the influence of compressed air. Examples include such elements as oil sumps, tanks for various liquids made of plastic or rubber hoses.

A method that is free from the above drawbacks is the thermal imaging method developed by Unitem. It enables the indication of the leak location and it is insensitive to pressure changes inside the tested element due to its deformation (after the introduction of compressed gas), which enables a significant reduction in the measurement time. Budowane thermal imaging leak testers distinguish between sealed and leaky elements by providing the traditional information OK and NOK . Optionally, it is possible to preview the thermograms in order to locate the leak. Examples of the leak test results of various components from the AutoMotive and household appliances industries are shown below.

Fig. 1. Tightness test of hose fittings installed in the cooling system of passenger cars a) view of the tested object, b) leakage in AR01 area.

Fig. 3. A) polymer tank mounted in cars, b) thermogram and c) exemplary temperature course

Fig. 5.a) The body of the heater used to heat water in coffee machines and b) view after dismantling, c) visible leakage on the embossing of one of the connectors (green temperature course and red area in the thermal image)

Fig. 2. Measurement of the tightness of the hose clamp a) view of the correctly made connection b) leak detected (black points on the infrared image)

Fig. 4.a) Thermal image of the local leak (red point) in the stainless steel diaphragm and b) an example of the temperature course during pressure shock changes (cyclical increase and decrease of Δp)

Fig. 6. Sample course and leak point thermogram (NOK). Test object: pneumatic hose

Acoustic methods

Acoustic leak detection uses sonic or ultrasonic energy generated by an expanding gas leak. This method is very simple and fast, but has low sensitivity – leaks down to 10 -2 mbar · l / s. Additional coverage of the leakage point with foam or water allows to increase the sensitivity range to 10 -4 mbar · l / s. This method is a vacuum and pressure method.

Air bubble method for leak testing

The air bubble method is one of the most widely used pressure methods. There are two variants of this method. In the first stage, the test object is pumped to a sufficiently high pressure and it is immersed in water, and thanks to the air bubbles formed, the leakage point can be located. In the second variant, the object is covered with a thin layer of an aqueous solution of soap or detergent and, after inflating, it is observed where the soap bubbles form. The sensitivity of this method for soap bubbles is approx. 10 -4 mbar · l / s, while for the method with immersion of the tested object it is approx. 10 -3 mbar · l / s. In the method with immersion of the tested object, the credibility is significantly influenced, among others, by lighting of the water reservoir, degree of water turbidity, location of the leak, and hence the sensitivity of this method is much worse.

Both variants of the described method, although apparently simple, often create many inconveniences. In the case of the immersion method, the problems increase with the size and weight of the tested objects, the more so as they must be thoroughly dried after the test. In the alternative, the removal of the previously applied solution is often quite laborious and therefore costly.

Air bubble tightness test with the use of a dedicated agent.


Slow pressure variation method (pressure drop method, differential method) for leak testing

Typical pressure plot during a leak test. This course has 4 characteristic phases: filling, stabilization, test and air discharge.

Source: and-dp / dt

Depending on the value of the pressure generated inside the tested object, the method of slow pressure changes is classified as either vacuum or pressure methods. In both variants, it allows to assess the tightness of the facility, , however, without the location of a possible leak.

The sensitivity of this method in the vacuum variant depends on the measuring range and accuracy of the vacuum gauge used. For the ionization vacuum gauge (p min = 10 -6 Pa) the recorded leaks reach the level of 10 -6 mbar · l / s. The principle of the pressure variant differs only in that the tested object is inflated to a pressure of a few atmospheres, and after disconnecting the compressor, the rate of pressure drop –Δp / Δt resulting from the actual leakage (pressure drop method) is measured. The sensitivity of the pressure gauges used is usually approx. 100 Pa (the lowest measurement resolutions are 0.01 Pa for the most expensive measuring devices) and therefore the sensitivity of this variant is several orders of magnitude lower than in the case of the vacuum variant.

The difference in the measured pressure drop (ΔP = P 2 – P 1 ) is influenced by several factors such as:

  • presence of a leak
  • volume difference ΔV
  • temperature difference ΔT

Therefore, when using the pressure drop method, one should take into account the influence of temperature change ΔT and the effect of volume change ΔV on the values ​​of the measured pressure drop ΔP. When using this method on the production line, you should be aware of the influence of the above physical quantities on the final result of the measurement. To eliminate the influence of these factors, use the differential pressure drop method. In other words, the differential method compensates for volume differences ΔV and temperature differences ΔT.

In the differential method, one of the basic applicable laws is Mariotte’s law (Boyle’s law), which for ideal gases takes the form:

P V = n R T

where: P [Pa] – pressure, V [m 3 ] volume, n – number of moles (amount of matter), R – constant for ideal gases (R = 8.31 J / mol · K) , T [K] – temperature.

After taking into account the influence of temperature change and volume change, we get:

(P + ΔP) (V + ΔV) = n R (T + ΔT).

The volume V consists of: the volume of the test element, the volume of pipes used to connect the tested tank, the volume of pipes and fittings inside the measuring device.

Tightness test using the pressure drop method with a standard element.

The figure shows the concept of measurement using the differential method, in which we use a standard (element with an acceptable level of tightness) made of the same material with the same dimensions (volume, structure) as the tested element. Both elements are placed under the same climatic conditions (temperature, pressure). Thanks to this approach to measurement, the values ​​of ΔT and ΔV are the same for the tested and standard element and cancel each other out without contributing to the measurement indicated by the leakage measurement device.

Methods using gas markers to test the tightness

Methods consisting in introducing selected gases (markers) into the tested tanks and tracking their flow through the leaks using detectors. Gas markers should meet a number of conditions: they should not be chemically active, toxic, they should not be present (in significant amounts) in the Earth’s atmosphere, they should not be explosive / flammable and should have the highest possible value of the diffusion coefficient to other gases. The only gas that meets the above conditions is helium, and it is often used. Sometimes hydrogen is also used as gas markers (usually a mixture of up to 5% hydrogen with nitrogen, which is not explosive) or one of the freons (nowadays very rarely). Hydrogen does not meet some of the above requirements, but its diffusion coefficient is of high value and is therefore used. The leak test method using gas markers can be used as a vacuum or pressure method.

Vacuum methods with the use of gas tracers for leak testing

The vacuum method with the use of gas markers requires attaching a mass spectrometer to the tank under test and pumping the entire set down to the operating pressure of the spectrometer. The construction of the spectrometer is selected so that it detects only the gas tracer molecules. The stream of this gas blows successively all tank joints. If the gas stream is directed to the leak, the gas gets inside the apparatus and then goes to the spectrometer, which registers its presence. In this method, the measurement of the leak rate requires some time (depending on the volume of the tank and the rate of pumping helium from the tank), although the leak itself can be located much earlier. The location of each subsequent leak requires the pumping of the gas tracer (e.g. helium) introduced during the previous test into the tested tank. The time it takes to remove helium is called the ventilation time. Response time and ventilation time characterize the inertia of the vacuum system as it changes and must be taken into account in leak detection procedures.

A professional leak detector is equipped with a quadrupole mass filter and an autonomous pumping system with a turbomolecular pump and an initial vacuum pump, which makes this system relatively expensive.

The sensitivity of the described method (the lowest value of the recorded flow rate) is very high and usually amounts to 10 -11 mbar · l / s.

Pressure methods with the use of gas markers for leak testing

Leak detector for use in domestic gas installations. There is no need for a tracer gas in this application, as the utility gas itself plays this role at the same time.

The tested vessel is filled with the pressure method using tracing gases (most often with a mixture of helium or other tracing gas with air) to a pressure exceeding atmospheric pressure, usually up to approx. 2 – 5 bar. Then the detector tip (with or without a suction cup) is placed successively on the tested surfaces of the tank, in particular all kinds of connections (detachable and non-detachable) in order to detect leaks. When the tracer gas reaches the detector sensor through the leak, it signals its presence. This method requires a detector with a relatively high degree of complexity:

  • Helium leak detector with mass spectrometer
  • vacuum system to maintain a sufficiently low pressure in the spectrometer (often a turbo molecular pump + back-up pump)
  • valves controlling the individual stages of the measurement cycle
  • electronic control and measurement system

The sensitivity of this method for the best solution is estimated at 10 -7 mbar · l / s. It should be remembered that the pressure method does not allow for a precise estimation of the leak rate.

The above method is also used in a much simplified variant, in which we obtain information about the location of the leak, while the conclusions about the size of the leak can be drawn on the basis of the value of the gas marker given in ppm (parts per million). Detectors of this type are often not equipped with suction cups, and the cost of the instrumentation is incomparably lower than in the mass spectrometer method. Unfortunately, in this variant, we do not have information about the gas flow rate through the leak.

Method Pressure method Vacuum Leak Location Method sensitivity range [mbar · l / s]
10 -2 10 -3 10 -4 10 -5 10 -6 10 -7 10 -8 10 -9 10 -10 10 -11
Acoustic Classic




Coated with water or foam










Slow pressure changes



Gas Tags


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