Sensing leakage

Valve. seat Fails to block flow when closed. Possible leakage of SIS fluid into system and reduced operability. Need leakage taps on system to determine if there is leakage between series valves. Sense temperature of pipe. Inspection. 

Motor Failure Bearing Motor cannot open valve Shorts can be sensed by ground leakage. 

As system pressure increases and approaches valve set pressure, it acts upward on the sense diaphragm, with the feedback piston moving upward to close the inlet seat, thus sealing in the main valve dome pressure, as the outlet seat is also closed. A small, further increase in system pressure opens the outlet seat, venting the main valve dome pressure. This reduced dome pressure acts on the unbalanced feedback piston to reduce feedback piston lift, tending to lock in" the dome pressure. Thus, at any stable inlet pressure there will be no pilot flow (i.e. zero leakage). 

Ritchie L.J., Ferguson C.P., Bessant C., Saini S., A ten channel fibre-optic device for distributed sensing of underground hydrocarbon leakage, J.Environ. Monitor. 2000 2 670-673. 

Size-related problems may become important for all microsensors. Leakage of sensing materials from a small membrane may lead to rapid deterioration of sensor properties [104], While the lipophilicity of membrane components cannot be increased infinitely, immobilization of ionophore and ion exchanger in the polymer by covalent attachment or molecular imprinting along with utilization of plasticizer-free membranes could help solve the leakage problem. 

When using the positive pressure method it is sometimes either impractical or in fact impossible to measure the leakage rate directly while it could certainly be sensed in an envelope which encloses the test specimen. The measurement can be made by connecting that envelope to the leak detector or by accumulation (increasing the concentration) of the test gas inside the envelope. The bombing test is a special version of the accumulation test (see Section 5.7.4). In the so-called sniffer technique, another variation of the of the positive pressure technique, the (test) gas... 

Because most UV equipment operates at voltages well above the mains level, it is important to prevent exposure to high voltage by proper installation. Microwave-powered lamps have a detector to sense microwave radiation leakage. The system is shut down when a microwave irradiance of 5 mW/cm2 is detected.3... 

Means for Preventing Tank Leakage. In addition to the common sense approaches, such as selecting corrosion, weather, and moisture-resistant materials of construction, providing excellent foundations, and leak-detection instrumentation, there are additional preventive measures that can be taken. Cathodic protection, for example, is described in an article on Corrosion. 

The typical pressure profile of the standpipe and the valve is shown in Fig. 8.18. As can be seen in the figure, the pressure head over the standpipe Aps, in the absolute sense, is equal to the sum of the overall pressure head, Apt, and the pressure drop over the valve, Ap0. From Eq. (8.92), the particle volume fraction in the standpipe can be estimated from the measured height of the bulk particles. Thus, given the particle mass flow rate, the leakage flow of gas in the standpipe can be estimated from Eq. (8.95). 

Because of all these differences between test and service conditions, shutoff specifications should be used mainly for comparing the capabilities of alternative valves rather than in an absolute sense. The buyer knows that a Class IV valve will leak much less than a Class II valve of a similar configuration—although one can never be certain just how much less, or exactly how much leakage can be expected in either case. 

Matthews, M.D., Jones, V.T. and Richers, D.M., 1984. Remote sensing and hydrocarbon leakage. Presented at 3rd Inti. Symp. Remote Sensing of Environment, Colorado Springs. 

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