Leakage test for air ducts
Leakage test for air ducts
Application note A053-GP06-0217D
Air and liquid tightness of devices is of utmost
importance. This is especially in the heating,
ventilation and air-conditioning (HVAC) sector,
where exhaust pipes of central heating systems
should not leak combustion gases. And also air
ducts installed in buildings, transporting huge
amounts of air, have to be airtight to some extent.
To comply with this directive, Bronkhorst has
developed a leakage test method. First only for air
ducts, later also for exhaust pipes of central heating
systems, and also employed for a liquid-tight oil
pumps in the automotive sector. This test can be
applied to closed systems as well as open systems,
temperatures and high pressures, to make the
reaction steps as effective as possible and it is related
to quality control: more and more ISO certifications
require the documentation of quantitative leakage
data.
 Air ducts
 Exhaust pipes
Housing of the flow pressure solution
(photo: Bergschenhoek)
Application requirements
The basic principle is simple: consider a ‘device
under test’, which may be everything, ranging from
a small hole to a volume of 10 liters. Apply a
pressure by a pressure controller (PC) to that
device, and measure any gas leakage using a mass
flow meter (MFM). The use of the specific PC and
MFM depends on the setting/measuring range.
Important topics
 Test to check or guarantee leak tightness
 Temperature stabilization
Process solution
PC
FI
DUT
A practical realisation of the measuring
principle is as follows. Place the device under
test (DUT) under a certain gas pressure as
specified by the customer, as the leakage rate
under that specific condition has to be known.
Suppose this initial pressure is 5 bars, then we
need to know what incoming flow is necessary
to balance the outgoing leakage, in order to
keep the pressure stable.
A pressure controller (PC) sets the pressure and
the gas flow is measured by a thermal mass flow
meter (MFM). Even a liquid-related application
can be tested in this way by performing gas flow
measurements. In the case of testing air ducts,
the gas is pressurised air delivered by the
customer’s compressor. Normal air can be used,
from which water and oil have been removed
prior to testing.
Flow scheme
However, there are some catches. In order to
eliminate the pressure drop over the MFM, the
PC needs to be as close to the DUT as possible,
so the PC and its valve need to be separated
physically. Furthermore, as normally several
DUT’s are tested in succession, two shut-off
valves have to be placed between the setting/
measuring equipment and the DUT, to reduce
testing time and to improve stability. Moreover,
especially for cases with a very small leakage
rate, a safe bypass has to be added to ... u
... the setup in order to fill the DUT quickly.
Using such a safe bypass avoids approving a
defect product. The solutions to all these
‘catches’ are shown in the flow scheme.
Temperature stabilisation prior to conducting a
measurement is essential. For example, due to
gas expansion a temperature variation of 2 °C
already results in a volume change of 0.7 %. Any
leaks smaller that this volume change cannot be
measured when the temperature fluctuates. 
(photo: Bergschenhoek)
Recommended Products
EL-FLOW Prestige
EL-FLOW Prestige is the next generation of
Bronkhorst Mass Flow Meters / Controllers for gases.
Nearly all core components have been redesigned
and many improvements and innovations have been
incorporated. Introducing the “Differential Temperature Balancing” technology, which ensures a superb
sensor stability.
EL-FLOW Select
EL-FLOW® Select Series Mass Flow Meters/Controllers
are thermal mass flow meters of modular construction with a ‘laboratory style’ pc-board housing.
Control valves can either be integrally or separately
mounted, to measure and control gas flows from
lowest range 0,014...0,7 mln/min up to highest range
8...1670 ln/min.
EL-PRESS
The EL-PRESS series digital electronic pressure
transducers and controllers for gases and liquids
have a well-proven compact thru-flow design. The
instruments include a diaphragm type piezo-resistive
pressure sensor for pressure measurement/control
from: lowest ranges 2 ... 100 mbar absolute, gauge or
differential up to highest ranges 8 ... 400 bar absolute
/ gauge or 0,3 ... 15 bar dif.
E-8000
Bronkhorst offers Power Supply / Readout and
Control Modules for use with digital Mass Flow
Meters / Controllers, Pressure Meters/ Controllers and
other transmitters and transducers with RS-232
communication. The E-8000 Series have one or two
colour TFT displays per module for indication of
measured/totalised values and a push button menu.
Contact information
Leakage tests
for air ducts
A053-GP06-0217D
T +31(0)573 45 88 00 F +31(0)573 45 88 08
I www.bronkhorst.com E [email protected]
GP:
06:
General Purpose
Leak detection
 High accuracy (standard 0,5% Rd plus 0,1% FS)
 Rangeability in digital mode up to 1:150
 Extremely fast and dynamic response
 An on-board gas conversion model
 Multi-Gas / Multi-Range functionality
 Pressure ratings 64 / 100 bar
 Analog I/O-signals, RS232-connection; optional
on-board fieldbus interface)
 High accuracy (standard 0,5% Rd plus 0,1% FS)
 Rangeability in digital mode up to 1:187,5
 Fast response (down to 500 msec), excellent
repeatability
 Optional Multi-Gas / Multi-Range functionality:
freely programmable ranges and gas types
 Pressure ratings 64 / 100 bar (Multi-Gas /
Multi-Range functionality up to 10 bar)
 Compact, modular construction
 Thru-flow design
 Compact arrangement
 Stable control, even at varying process volumes
 High pressure capability up to 400 bar
 Metal sealed and/or down-ported versions
available
 High accuracy and repeatability
 Bright, wide angle, 1.8” display (TFT technology)
 User friendly operation
 Programmable alarm functions
 Fluid selection (up to 8 fluids/curves)
 Indication/operation/configuration of measured
value, setpoint, totalised flow, fluid/tag number,
control characteristics, fieldbus settings
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