Processing, April 2020
A PRV may never be called upon to operate in an emergency but when needed it must perform in a very specific manner 40 Processing APRIL 2020 vibration due to turbulence because nothing is flowing through it When system pressure exceeds the set point it opens releasing the contents of the system liquid gas or both This creates turbulence generating mechanical vibrations that an acoustic monitor can detect and report to the automation system If the process recovers and system pressure returns to normal or operators reduce pressure sufficiently the PRV should close again automatically If everything is working correctly it will seal and the mechanical vibration will cease Data from the acoustic transmitter can verify the action reporting the time the discharge began and ended while giving some approximate indication of how serious the discharge was based on the amplitude of the sound But sometimes things go wrong and a small particle of debris from the process can get in between the valve and its seat causing leakage Figure 5 This can happen with either type of valve but tends to be more of a problem with direct spring load metal seated PRVs Pilot operated PRVs have soft seats and are not as likely to trap debris but it can still happen therefore some users install acoustic transmitters on pilot operated PRVs as well Like a full overpressure driven release small leakages also generate turbulence inside the discharge pipe causing mechanical vibration detectable by the acoustic transmitter Usually the amplitude of a leakage detection is smaller than a full release which helps differentiate these two events via measurements from a single acoustic transmitter Figure 5 This graph illustrates a typical leakage event After the first blow down the valve does not shut completely Leakage shown by the blue line persists but is detected by an increase in acoustic level shown by the green line
You must have JavaScript enabled to view digital editions.
