When valves leak or fail, it can be extremely costly in terms of product quality, safety and energy loss. Valve operation effects the way fluids will flow through a system.
There are great differences in the way particular valves work (for example, control valve versus safety valve). An Ultraprobe makes it easy to adjust for these differences and readily determine operating conditions while valves are on-line.
How Ultrasonic Valve Leak Detection Works
As fluid moves from the high pressure side of a valve through the seat to the low pressure side, it produces turbulence. This turbulence generates ultrasound which is detected by the Ultraprobe and translated, via heterodyning, down into the audible range.
The translated ultrasounds are heard through headphones and seen as intensity increments, usually decibels on a display panel. High frequency tuning allows users to adjust for differences in fluid viscosity (i.e. water vs. steam) and reduce any interference from stray pipe noises. Ultrasound spectral analysis provides an “image” of sound to help determine fluid flow characteristics. Using the time series screen it is possible to determine low, medium or high flow conditions.
Leak Detection Method
Inspection methods vary depending on the type of valve. Therefore the primary rule is to know the details of your system, including the way a specific valve may work under specific conditions.
For example, is the valve normally open or normally closed? In order to determine valve condition such as leakage or blockage: touch two test points upstream of the valve (points A and B). On the first test point (test point “A”) reduce the sensitivity (received amplitude) of the instrument until the intensity indicator on the display panel reads about 50% of scale.
If the instrument has frequency tuning, you may also use this feature to hear the valve sound quality more clearly by changing the frequency. Simply tune the frequency (usually 25 kHz) until the sound you would expect to hear becomes clear. It’s that simple.
Next, touch two test points downstream of the valve (points C and D) and compare intensity levels. If the sound is louder when comparing the first downstream (C) with the second upstream test point (B), the fluid might well be is passing through. If the compared downstream sound level is low, the valve is closed. If the second downstream test point (D) is louder than the first downstream test point (C), this indicates the sound is transferred from a source further downstream and indicates the valve may not be leaking.
Ultrasonic valve inspection is considered a “positive” test in that an operator can instantly identify sound quality and intensity differentials and thereby determine operating condition accurately. Sound analysis can also be used to indicate the amplitude and movement of fluid between the upstream and downstream test points.