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5. LOCATING FAULTY VALVES: Utilizing the Contact (Stethoscope) Module in the Ultraprobe, valves
can easily be monitored to determine if a valve is operating properly. As a liquid or gas flows through a
pipe, there is little or no turbulence generated except at bends or obstacles. In the case of a leaking valve,
the escaping liquid or gas will move from a high to a low pressure area, creating turbulence on the low
pressure or "downstream" side. This produces a white noise. The ultrasonic component of this "white
noise" is much stronger than the audible component. If a valve is leaking internally, the ultrasonic
emissions generated at the orifice site will be heard and noted on the meter. The sounds of a leaking valve
seat will vary depending upon the density of the liquid or gas. In some instances it will be heard as a subtle
crackling sound, at other times as a loud rushing sound. Sound quality depends on fluid viscosity and
internal pipe pressure differentials. As an example, water flowing under low to mid pressures may be easily
recognized as water. However, water under high pressure rushing through a partially open valve may sound
very much like steam. To discriminate:
1. Reduce the sensitivity. 2. Change the frequency to 25 kHz and listen.
A properly seated valve will generate no sound. In some high pressure situations, the ultrasound generated
within the system will be so intense that surface waves will travel from other valves or parts of the system
and make it difficult to diagnose valve leakage. In this case it is still possible to diagnose valve
blow-through by comparing sonic intensity differences by reducing the sensitivity and touching just
upstream of the valve, at the valve seat and just downstream of the valve (see "Confirming Valve Leakage
In Noisy Pipe Systems).
PROCEDURE FOR VALVE CHECK
1.
Use
Contact
(Stethoscope) Module.
2.
Touch downstream side of valve and listen through headset.
3.
Start test at 40
kHz
. If the sound appears weak or confusing, change the frequency. As an example, try
to test at 30
kHz
. then 20
kHz
.
4.
When necessary, if there is too much sound, reduce sensitivity.
5.
For comparative readings, usually in high pressure systems:
a. Touch two equidistant points on the upstream side (test points A and B). Reduce sensitivity to get a
dB
reading in each. .
b. Touch valve seat and/or downstream side.
c. Compare sonic differentials. If the valve is leaking, the sound level on the seat or downstream side
will be equal to or louder than the upstream side.
6.
In some instances, such as in noisy background or low viscosity fluids, it will be helpful to adjust the
frequency to adequately interpret valve sounds.
To do this:
a. Touch upstream of the valve and, in the
Frequency Select Mode
, gradually Spin the
Sensitivity
Control Dial
until the stray signals are minimized or until the desired fluid flow is heard clearly.
