Wöhler UL 23 / US 23
EN
As the device is able to detect leaks in different types of medium (gas, liq-
uid), there is a great number of different applications, especially in the sec-
tors heating, air-conditioning, buildings. So the UL 23 is an effective and
cost saving device that helps the workman and the ingenieur to resolve
many leakage-problems.
2. Principle of Operation
A leak is any unwanted flow of a substance out of a system, or in a vacuum
into the system. Friction in flow generates sound, water in pipes creates
sound as well as air out of a tire. The sound we can hear is less than a third
of the total sprectrum of frequencies generated. The sound in small leaks is
mostly ultrasonic. Humans cannot hear this because it is above the human
hearing range. In order for a leak to generate ultrasound, the flow through
the leak path must be turbulent. For this to happen the velocity that a gas is
moving through the leak point must be high in relation to the orifice. The UL
23 receives the ultrasonic sound that escapes from a leak point, processes
it, and displays its strength. The larger the leak, the higher the indication. In
addition to the display, it produces an audio reproduction of the leak sound.
The intensity of the audio will change proportionally to the display.
The principle of operation of the UL 23 is based on the turbulent flow of
fluids and gases, turbulent flow has a high content of ultrasound. This is
sound which is above the human hearing range, but can be heard with the
UL 23, and traced to its source. Imagine air leaking from a tire. Because
this is such a large leak, your ear can detect this sound, however your ear
hears only about 1/3 of the actual spectrum of sound which exists. The
sound of small leaks is mostly ultrasonic so that your ear cannot detect it.
It is important to remember this example: A piece of straight tubing con-
nected to a gas supply and left free to exhaust into the atmosphere will not
generate sound, if the volume of gas through it is such that turbulence does
not take place. Yet for that same flow, an opening as small as 0.005 of an
inch could generate enough sound to be heard several feet away.
For a leak to happen there must be an opening in the system that carries a
gas or fluid. Normally, these openings are not clean smooth holes, but pas-
sages through cracks with many jegged edges and internal chambers. Flu-
id or gas escaping through an orifice like this, is forced into turbulence,
random circular-like motions. Inside a tube where a gas may be flowing, the
flow is normally laminar which means that a given layer of gas does not mix
with layers above it or below it. This condition happens in a straight long
tube, when the velocity of the fluid is not high. A gas leak out of a straight
and long tube will not generate as much sound as if it were leaking out of a
small crack because the flow is not turbulent.