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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.
Ds
To discriminate:
1. reduce the sensitivity until the meter reads about mid-line.
2. change the frequency down to about 20-25 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", page 26).
Procedure For Valve Check
1. Use stethoscope module.
2. Select LIN in meter mode dial.
3. Touch downstream side of valve and listen through headset.
4. Start test in FIXED BAND on Frequency Selection dial. If the sound appears weak or confusing, change the
frequency. As an example, try to test at 40 kHz, then sweep down in frequency to 20 kHz.
5. When necessary, if there is too much sound, reduce sensitivity.
6. For comparative readings, usually in high pressure
systems:
a. Touch upstream side and reduce sensitivity to minimize any sound (usually bring the meter to a mid-line
"50" reading).
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.
7. 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.
