Solenoidcontrolled systems

Instrumentation and Process Control

  • Question 1

    A {\it burner management system} (BMS) monitors the status of the flame at the base of this incinerator, to ensure fuel gas does not keep entering the combustion chamber unless there is an established fire to burn it:

    Explain the purpose of solenoid valve SV-115, identifying whether it is normally energized (NE) or normally de-energized (NDE).

    Also, explain the purposes of SV-111, SV-112, and SV-113 in this incinerator control system.

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  • Question 2

    Solenoid valve SV-92 plays an important role in this compressor inlet separator control system. Level control valve LV-92 opens up when needed to drain liquid out of the ``boot’’ of the separator vessel, which ideally contains only gas (vapor). Examine this P\&ID and then answer the following questions:

    {\bullet} Identify the statuses of SV-92 and LV-92 when the separator boot liquid level is at or below the normal level of 1 foot 4 inches.

    {\bullet} Describe how this system responds to high liquid levels in the separator boot.

    {\bullet} What will be the consequence of an instrument air supply failure, as it relates to the separator boot liquid level?

    {\bullet} What will be the consequence of an AC power failure to LIC-92?

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  • Question 3

    This loop sheet shows a pneumatic reactor temperature control system utilizing a solenoid valve to assist in the actuation of process valve TV-135:

    Determine the following, based on a close inspection and analysis of the diagram:

    {\bullet} The typical status of the output switch contact on TY-135 ({\it NO} or {\it NC})

    {\bullet} The effect of an AC power loss from breaker \#4

    {\bullet} The effect of the solenoid vent becoming plugged or accidently capped by a technician

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  • Question 4

    Determine the ``normal energization’’ states (e.g. NE or NDE) of each solenoid valve in this diagram, assuming the process valve needs to be {\it closed} when the process is running as it should:

    Also, determine whether one or both solenoids need to ``trip’’ in order to make the process valve go to its fail-state. In other words, is this a {\it 1oo2 to trip} system, or a {\it 2oo2 to trip} system?

    Suppose the ball valve refused to shut off when it should. Identify at least two possible faults that could cause this to happen.

    {\bullet} Suppose the probability of each solenoid valve ``sticking’’ in its regular operating position instead of tripping when commanded is 4.5 $\times 10^{-3}$. Calculate the probability of the process valve refusing to trip when commanded as a result of this type of failure.
    {\bullet} Suppose the probability of each solenoid valve ``sticking’’ in its tripped position instead of going to its regular operating position when commanded is 3.7 $\times 10^{-3}$. Calculate the probability of the process valve refusing to go to its regular operating position when commanded as a result of this type of failure.
    {\bullet} Suppose the probability of each solenoid valve accidently tripping during regular operation is 9.5 $\times 10^{-4}$. Calculate the probability of the process valve tripping accidently as a result of this type of failure.

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  • Question 5

    Sketch arrows next to each of the two solenoid valves showing the directions of air flow in the energized (E) and de-energized (D) states, assuming both of the solenoid valves must ``trip’’ in order to force the process valve to go to its ``fail’’ position (i.e. 2oo2 to trip):

  • Question 6

    Sketch arrows next to each of the two solenoid valves showing the directions of air flow in the energized (E) and de-energized (D) states, assuming the process control valve is supposed to be open in regular operation and close if both of the solenoid valves ``trip’’ (i.e. 2oo2 to trip):

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  • Question 7

    This fluid diagram shows the components and connections of a Bettis self-contained hydraulic module used to automatically shut off a ``line valve’’ on a natural gas pipeline in the event of the pipeline pressure going outside of its limits (either falling below the low-pressure limit or rising above the high-pressure limit):

    Identify all spool valve positions, and also trace the direction of oil flow, following a solenoid ``trip’’ event.

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  • Question 8

    Suppose this valve control system has a problem. The control valve (LV-104) does not move to the full-open position as it should when the solenoid is de-energized, although it will move when the 4-20 mA current signal to the I/P transducer is varied while the solenoid is energized:

    Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for {\it all} measurements and symptoms in this circuit.

    $$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Manual valve in ``bypass’’ position & & \\ \hline Solenoid coil failed open & & \\ \hline Solenoid coil failed shorted & & \\ \hline Solenoid valve (UY-104) spool stuck & & \\ \hline Solenoid valve (UY-104) vent plugged & & \\ \hline Air supply to LY-104 failed & & \\ \hline 4-20 mA signal wiring to LY-104 failed open & & \\ \hline 4-20 mA signal wiring to LY-104 failed shorted & & \\ \hline Control valve (LV-104) stuck & & \\ \hline \end{array}$$

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