Test methods

Leak tester / test methods

We assess your specific testing situation, configure its leak testers according to the needs of the task and offer trial measurements and initial sample inspections in our laboratory.

Index of contents / Test methods with compressed air

1. Differential pressure measurement procedure

1.1 Pressure dropping-/ decrease measurement procedure
1.1.1 Absolute pressure procedure LTC-602 A
1.1.2 Relative pressure procedure LTC-602 R
1.1.3 Dosing measurement procedure LTC-602 D

2.1 Pressure increase measurement procedure LTC-602 S

3. Flow test procedure with reference LTC-602 M
4. Flow measurement device LTC-602 Q

1.1.1 Absolute pressure procedure with LTC-602 A

The pressure drop/decrease is by far the most used method for leak testing.

Test medium:
Compressed air/vacuum, nitrogen, hydrogen, helium

Identifiable leak rates:
Volume and pressure-dependant > 1 cm3/min

Method:
Testing under pressure/vacuum. The change in pressure (drop in pressure) caused by leaks is measured and evaluated.

Pros:
  • simple, quick and cost-effective method
  • clear tools
  • few requirements on operating and maintenance staff
  • automated testing procedure possible
  • evaluation independent of operators

Cons:

  • usable pressure differential resolution depends on test pressure and volume
  • thermal and elastic changes to the test piece influence the outcome of the measurement, for leak rates < 1 cm3/min most cannot be used

1.1.2 Relative pressure procedure with LTC-602 R

The pressure decrease procedure is by far the most used procedure in leak testing.

Test medium:
Compressed air/vacuum, nitrogen, hydrogen, helium

Identifiable leak rates:
Volume- and pressure-dependent > 1 cm3/min
With very small volumes also < 1 cm3/min

Method:
Testing under pressure/vacuum. The change in pressure in the test piece caused by leaks is measured and evaluated by a sensor against an internal reference.

Pros:
  • all attributes as absolute pressure procedure
  • good measurement signal resolution, even with high test pressure
  • Reference volumes with elastic parts also advantageous as better compensation of volume expansion
  • if applicable, external reference with complex or elastic
Cons:
  • somewhat more expensive due to the use of an additional pressure difference sensor that measures against a differenceparts
  • not suitable for large drops in pressure or burst tests

1.1.3 Dosing procedure with LTC-602 D leak tester

Pressure drop/decrease method with determination of volume for
closed components or for determining the volume.Test medium:
Compressed air/vacuum or nitrogen

Identifiable leak rates:
Volume and pressure-dependant > 1 cm3/min

Identifiable differences in volume:
Pre-charge volumes > 2-3 %, depending on test piece volumes/reference ratio

Method:
A known pre-charge volume is pressurised/placed under vacuum and stabilised. This volume of gas is then fed into the test piece or test piece chamber. The resulting pressure is a measurement of the volume. The subsequent change in pressure due to leaking is measured and evaluated.

Attributes:

  • simple and cost-effective method
  • Volume can be determined and closed parts tested

2.1. Pressure increase procedure with Leak tester LTC 602 S

Test medium:
Compressed air/vacuum or nitrogen

Test pressures up to 500 bar possible

Identifiable leak rates:
Volume and pressure-dependant > 1 cm3/min

Method:
Testing under pressure/vacuum. The pressure change caused by leaks in the bell jar, which encases the test piece, is measured and evaluated. Sometimes also used in combination with pressure drop procedure (e.g. for oil cooler)

Pros:

  • any high pressure (up to 500 bar) possible
  • very fast testing procedure because the slow-down phase is omitted
  • small leak rates up to 0,1 Ncm3 / min possible
  • evaluation is irrespective of the operator

Cons:

  • often there is a high mechanical effort required, due to the use of a volume optimized bell jar
  • test piece and adaption are nearly or completely not visible through the bell jar
  • A leaky bell jar can lead to incorrect results

3. Flow test procedure with reference with LTC - 602 M

Test medium:
Compressed air/vacuum or nitrogen

Identifiable leak rates:
Volume and pressure-dependant > 0.5 cm3/min

Method:
Testing under pressure/vacuum. Escaping air due to leaks is offset via a reference volume. The compensating flow is determined via a mass flow sensor and is a measurement of the leak rate.

Pros:

  • even with large volumes, low leak rates of a few Ncm3/min can be measured
  • short measurement time is possible as mass flow response time < 1 sec.
  • low leak rates up to 0.1 Ncm3/min possible

Cons:

  • more outlay in measurement device due to required reference
  • the ratio of reference to test piece volumes should not exceed 5:1

4. Flow measuring device / Leak tester LTC 602 Q

The LTC-602 Q flow measurement device is a measurement computer for measuring the flow of gases. The device is available in different pressure levels and with different flow measurement ranges.

Test medium:
Compressed air, nitrogen, special designs for water, further on request

Test pressures:
in different measurement ranges, continuous from 0.1 - 20 bar

Flow measuring range:
1.5 - 50 ml/min, resolution 0.5 ml/min with high performance resolution
Flow ranges up to 400 Nl/min, special design even higher.

Method:
Measurement is optionally via a thermal mass flow or laminar element.

Useful principles

You will find everything you need to know about leak detection in our leak detection info sheet.