Leak testing dictionary

(Symbol p; unit Pa)

The pressure relative to empty space. Absolutely empty space defines the pressure zero point.

[According to EN 1330-8]

A measuring device that measures the absolute pressure.

[According to EN 1330-8]

A conductance leak having a diameter much greater than the leakage path length.

NOTE: It may be considered an opening in a very thin wall.

[According to EN 1330-8]

See Virtual leak

The pressure of the atmosphere at a specified time and place.

[According to EN 1330-8]

See Bombing

In the case of a leak test using a pressure change method, the balancing phase gives the system the necessary time to minimize undesirable contributions to the pressure change that result from an effective leak. Typical disruptive factors are the thermal effects due to inhomogeneity of the temperature in the gas and the test object and physical effects due to evaporation or condensation of vapors in the test object. The duration of the balancing phase is heavily dependent on the test object and the ambient conditions and is usually calculated empirically.

See Tight chamber

Bell testing during leak testing with air

The meaning of the term bell testing in the context of leak testing with air is explained under the leak testing method.

Bell testing during tracer gas leak detection

An integral test in which the test object is placed in a soft enclosure at atmospheric pressure.

NOTE 1: If the test object is under vacuum, the enclosure is filled with tracer gas and the leak detector is connected to the inner volume of the object.

NOTE 2: If the test object is pressurized with the tracer gas, the leak detector is connected to the enclosure/bell.

A gas sniffer or a gas detector (He / H2) can be used as the leak detector.

[According to EN 1330-8]

A test in which sealed test objects are subject to a back pressurizing process prior to testing them in a vacuum chamber.

[According to EN 1330-8]

See Bubble testing

A leak testing method in which leaks from test objects subject to excess pressure can be found by completely immersing them in a test liquid (water) or by covering their surface with a surfactant solution (foaming agent). The pressure in the test object is therefore high enough to indicate leaks by bubble formation.

[According to EN 1330-8]

Calibration in general and in leak testing with air

Refers to the measurement and documentation of the deviation of a measuring device test compared to a traceable standard.

Calibration of a mass spectrometric leak detector:

The setting of the sensitivity or calibration factor of a leak detector so that the display change is equal to the leakage rate of a test leak.

[According to EN 1330-8]

See Balancing phase

Conductance leak where the diameter is small in relation to the length.

This can mean both bell testing and the accumulation testing.

Also see Bell testing
Also see Accumulation testing

(symbol nB)

The ratio of the number of atoms or molecules of a given constituent to the total number of atoms or molecules in a mixture. For gases, this ratio is equivalent to the volume fraction (symbol c).

[According to EN 1330-8]

A leak which consists of one or more discrete openings, including porous areas, through which a fluid may flow.

[According to EN 1330-8]

A mass spectrometric leak detector where the tracer gas enters through the backing line into the outlet of the high vacuum pump and the partial pressure of the tracer gas is measured on the high vacuum side of this pump.

[According to EN 1330-8]

The volume of the leak testing system added to the volume of the test object.

[According to EN 1330-8]

See Minimum detectable leakage rate

A mass spectrometric leak detector where the gas from the inlet line enters through the high vacuum pump and the partial pressure of tracer gas is measured on the high vacuum side of this pump.

[According to EN 1330-8]

The pressure displayed by a pressure gauge that measures relative to atmospheric pressure.

[According to EN 1330-8]

Also see Relative pressure

In this phase, the test object is filled to a pressure level equivalent to the test pressure. The duration of the filling process (filling time) is dependent on the volume of the test object and the pressure value.

The filling phase can be preceded by a pre-filling phase. This preparation phase is intended to pre-stress and mechanically stabilize the test object and to minimize the thermal effects in the tracer gas. Duration and pressure value are calculated empirically. Typically, the pre-filling pressure is 10–20% higher than the filling pressure.

The pressure at which the measurement is executed. This is typically specified as relative pressure

See Relative pressure
See Filling phase

See Filling phase

(For gas flow through a line, part of a line, or an orifice) (symbol C, U; unit m3/s): The quotient of the pV throughput and the difference in the pressures prevailing at two specified cross sections or at either side of an orifice, assuming temperature uniformity in the system.

[According to EN 1330-8]

The property of a non-porous material to allow gas to pass through under a partial pressure difference by a process of solution/diffusion.

[According to EN 1330-8]

(Mass: Symbol qM; unit kg/s

Particles: Symbol qN; unit s/1

Molar: Symbol qv; unit mol/s)

The rate at which a quantity of gas passes through a given cross section of the system. The flow rate is given as the number of moles, the mass, or the number of particles moving per unit of time.

The flow rate is expressed in moles per second, kilograms per second, or 1/second (for particles).

For gases, the volume flow rate (volume: Symbol qV; unit m3/s) is a measure of quantity only under specified conditions.

[According to EN 1330-8]

Leak detector that responds to helium (4He) tracer gas.

[According to EN 1330-8]

The ideal gas in physics and physical chemistry is an idealized model of a real gas that precisely fulfills the relationship pV=nRT

where:
n = m/M;
p = pressure;
V = volume;
m = mass of the gas;
M = molecular mass;
R = universal gas constant;
T = absolute temperature.

See Integral leakage rate

The sum of all leakage rates from all leaks in an object, expressed as pV throughput.

[According to EN 1330-8]

A leak test which allows the integral leakage rate of a component to be determined. Integral testing methods include the pressure change test, the accumulation test, and the vacuum test.

In non-destructive test technology, a hole, porosity, permeable element, or other structure in the wall of a test object capable of passing gas from one side of the wall to the other due to a pressure or concentration difference.

[According to EN 1330-8]

Also see Leakage rate
Also see pV throughput

The term leak calibrator refers to a device in which the leak rate can be adjusted using a precision needle valve depending on the pressure.

Similar to a test leak, the unit is used for checking leak testing equipment/leak testing devices.

See Leakage rate

(also known as tightness testing, leak test, leakage testing, or leakage test)

Leak testing is a non-destructive test method in which leaks in a test object are identified by the flow of gas or liquid and the obtained value, converted to the actual leakage rate under operating conditions, is compared with the maximum allowable leakage rate.

Leak testing is always a comparative measurement.

Also see Tight

The pV throughput of a specific fluid which passes through a leak under specific conditions.

[According to EN 1330-8]

The differential pressure method (DD method) is an improvement on the relative pressure method. In this method, the test object and an additional reference volume are filled with compressed air during the filling phase. A differential pressure sensor is connected between the test object and the reference volume. After the system is separated from the pressure supply and balanced, the pressure difference between the test object and the reference volume is calculated over time. This value corresponds to the pressure change in the test object and can be used to calculate the leak rate. Since the pressure difference between the test object and the reference volume is very small regardless of the test pressure, the pressure range of the differential pressure sensor can be much smaller than the test pressure. This enables a typical resolution of 0.1 Pa and even smaller in special cases.

The differential pressure method is used when high resolution is required at higher pressures. The technical setup is more complex than with the relative pressure method.

In the direct flow method (DF method), the test object is subject to pressure directly from a mass flow sensor. The gas flow through the leak is measured directly.

The process is very fast and particularly suitable for large leak rates.

The reference flow method (MF method) is a variant of the differential pressure method which is particularly suitable for large volumes. If the test object is very large and the leak very small, an extremely long measurement time is required to produce a detectable pressure drop. With a mass flow sensor (typically a calorimetric sensor), a leak can be measured directly without waiting until a measurable change in pressure develops. The setup is the same as with the differential pressure method, but a mass flow sensor replaces the differential pressure sensor. The mass flow sensor is activated (bypass valve) once the test object and the reference volume are filled. A leak in the test object will cause a compensation flow between the reference volume and the test object. This flow is immediately detected by the sensor. The measured mass flow is not exactly equivalent to the test object leak value; rather it is dependent on the ratio between the test object and the reference volume.

The resolution is determined by the sensitivity of the mass flow sensor.

The relative pressure method (RD method) is the basis for all pressure change tests. It allows a compact setup and is characterized by high reliability as well as a wide measuring range. In this method, the test object is pressurized and is then shut off from the air supply using a valve. The pressure change is then calculated over time. A single relative pressure sensor is used to measure the pressure change and the test pressure. The measuring range of the sensor corresponds to the maximum test pressure. The pressure change is dependent on the test volume and the test pressure. The pressure change becomes more prominent as the test volume decreases. The resolution of this method is dependent on the measuring range of the sensor (maximum test pressure). This method enables a typical resolution of 1 Pa.

All leak testing methods which use air as the test medium. Depending on the method of detection used, reference is made to a “pressure change test”, a “bubble test”, or “flow testing”.

An instrument that can separate ionized atoms or molecules according to their mass-to-charge ratio and measure the corresponding ion current. The output signal is proportional to the partial pressure of a particular gas in the mixture.

[According to EN 1330-8]

A leak detector in which the sensing element is a mass spectrometer, adjusted to respond only to the tracer gas.

[According to EN 1330-8]

In a leak measuring device (relative pressure or differential pressure method), the measuring phase is the time interval over which the pressure drop is measured.

The duration of this interval is dependent on the test object and the limit values:

The larger the volume, the more time is needed to determine a discernible pressure drop.

The smaller the leak, the more time is needed to determine a discernible pressure drop.

The higher the desired measuring accuracy, the more time is needed to achieve a stable result.

In leak testing with the flow method, this phase corresponds to the time interval during which the flow rate, which directly reflects the leak rate, is read. The duration of the phase is very short and it has a negligible effect on the measurement results.

See Measuring phase

The smallest leakage rate that an instrument, method, system is capable of detecting under test conditions.

[According to EN 1330-8]

A leak of such a geometric configuration and under such pressure conditions that gas flowing through it obeys the laws of molecular flow.

[According to EN 1330-8]

Leak rate defined by the volume that a gas quantity escaping from a leak occupies at standard pressure and temperature (0°C and 1013 mbar). The specification of normalized leakage rates is mostly used to compare results measured under different ambient conditions.

(Symbols: pA, pB)

The pressure that would be exerted by a gas or vapor of a mixture if it alone was present in an enclosure.

[According to EN 1330-8]

The pre-filling phase can precede the filling phase. This preparation phase is intended to pre-stress and mechanically stabilize the test object and to minimize the thermal effects in the tracer gas. Duration and pressure value are calculated empirically. Typically, the pre-filling pressure is 10–20% higher than the filling pressure.

A leak test in which the rate of the total pressure change, drop or rise, in a test object is measured.

The leak rate can be calculated directly as a pV throughput.

[According to EN 1330-8]

A leak test in which the rate of the total pressure drop in a test object is measured. The leak rate can be calculated directly as a pV throughput.

[According to EN 1330-8]

See Pressure change test

A leak testing method in which a liquid containing a dye or fluorescent oil is driven by a pressure differential into the leak in the wall of the object to be tested and then detected by a visual inspection on the other side.

[According to EN 1330-8]

(Symbol qG; unit Pa·m3/s)

The rate at which a volume of gas at a specified pressure passes a given cross section of the system. NOTE: If pV-throughput is used to characterize the flow rate of gas, as is common practice in leak testing, the temperature and molecular mass or density are given in addition so that the flow rate can be calculated using the ideal gas equation.

[According to EN 1330-8]

See Leak calibrator
See Test leak

Pressure which is measured relative to a known reference pressure (typically atmospheric pressure).

Also see Excess pressure

The time that it takes for a certain percentage of the output signal to be measured in the tracer gas leak detector. The output signal is measured as soon as an equilibrium pressure is established between the volume slowly filling with tracer gas and the tracer gas leak detector.

[According to EN 1330-8]

A leak testing method in which the test object is filled with tracer gas under pressure. The tracer gas escaping through leaks is detected by a sniffer probe, either directly or by accumulation in a chamber or enclosure.

[According to EN 1330-8]

A device that can be used to pick up tracer gas from an area of the test object and feed it to a leak detector at the necessary low pressure.

[According to EN 1330-8]

A test leak, the leakage rate of which can be traced to a fundamental leakage rate standard.

[According to EN 1330-8]

See Dead volume

In leak testing, the actual conditions of ambient temperature and pressure under which the test is performed.

[According to EN 1330-8]

See Leak calibrator

A flange placed at the beginning of the inlet line used to couple the test object to the leak detector.

[According to EN 1330-8]

The test time is the duration of the entire measuring process. The measuring process consists of the pre-filling, filling, balancing, measuring, and venting phases. The test time is the sum of the duration of all phases. It is not to be confused with the measurement time.

Also see Measuring phase

See pV throughput

Free from leaks according to a given specification.

The zero leakage rate must not be specified. The required tightness must be related to the function of the object to be tested.

[According to EN 1330-8]

A sealed encasement which fully envelops the test item during a leak test which can be pressurized or evacuated to subject the test object wall to a pressure difference.

[According to EN 1330-8]

A fluid (gas, liquid) which can be detected by a specific detector after it has passed through a leak, therefore indicating the presence of a leak.

[According to EN 1330-8]

The background signal that comes from the tracer gas from the system and not from the actual leak. The underground signal results from the tracer gas concentration in air in unpolluted ambient air. This is 5 ppm for helium and 0.5 ppm for hydrogen. The partial pressure corresponding to this concentration results from the product of absolute pressure and concentration.

[According to EN 1330-8]