Impulse line

Check isolating valves at process impulse line see that equalizing valve is shut. 

Impulse lines may be plugged with process solids. 

The impulse lines—electrical or pneumatic—leading to EIVs should also be fire-protected [I I]. 

The author implies that the impulse (line 2 7) to create a government report on smoking... 

A small block valve is usually installed at a tank on any instrument impulse line just in case a leak develops on the small tubing. In this unit block valves are generally avoided on overpressure or vacuum relief devices. If a block valve that can defeat an overpressure device cannot be avoided, such a valve is chained and locked open or car-sealed opened and a protocol is developed to administratively control accidental closing of such a prime safety feature. 

VALVE 4 = IMPULSE LINE ISOLATION VALVE TO P/V AND N2 REGULATOR... 

With all due respect to the findings of the investigating team, the root cause appears to me to be a human factors situation. The new piping system looked simple but in fact this unique system was confusing. A check valve (valve no. 2) was installed on the vent header to prevent cross-contamination. A small block valve (valve no. 4) was installed on the vacuum relief impulse line to provide easy isolation. [5]... 

If an instrument or instrument system malfunctions, the operator tries to correct the problem. If an alarm, flow- or temperature-measuring instrument or shutdown system malfunctions, the operator s first response should be an attempt to restore it to service. It may be a plugged impulse line, inadvertent flow shut off to an analyzer, etc. If the Instrument System is a Class 1 or 2, immediately go to Step 2. If the alarm is a Class J. the Lead Operator (or Shift Foreman) should be consulted and follow established procedures and his knowledge of the unit and the specifics of the situation to determine the temporary steps required. At the minimum, a note in the maintenance logbook must be made to initiate repairs. Stop Here for Class 3 Alarms. 

A hot fan (Fi) in Figure 2 acts in a push-pull mode to suck gases from the reactor and pressurize them to move through the circuits. The volume of recirculated gas through the heat exchanger-reactor loop is set by valve V2. The off-gas valve vy operates automatically in response to a pressure impulse line in the top of the reactor above the wood feed. This line provides a pressure signal referenced to ambient barometric pressure for adjusting to accomplish the desired pressure differential. Typically this is set at zero or minus 3.0 Pa to prevent wood gas escape... 

The prime consideration for instrument connections is to avoid hydraulic interference in the column or impulse line, which would lead to erroneous measurements or instrument malfunction. False information supplied by instruments has been the cause of premature flooding, column damage, and poor separation in many columns. This chapter examines the preferred practices, reviews common pitfalls, and supplies guidelines for avoiding pitfalls with column instrument connections. 

The connection(s) must be compatible with the instrument and permit correct installation of impulse lines. Figure 5.36 and c shows a case where overlooking this guideline prompts incorrect readings (see guideline 3 in Sec. 5.3 for details). Defective impulse line piping is one of the most frequent sources of instrument problems. 

Where ambient temperatures can fall below the freezing point of water (or of the process fluid), the possibility of liquid freezing in impulse lines must be averted. Extensive discussions are presented elsewhere (120, 266). 

All instruments, except for those that are directly required for monitoring the line-blowing operation, should be disconnected or at least blocked off dming line blowing to avoid debris entering the impulse lines. With the impulse-lines disconnected, the tie-ins of the instruments to the lines should be blown free of debris just before blowing a line is terminated. 

Troublesome impulse lines This is one of the most common instrument problems. Impulse lines are discussed at length in Chap. 5. 

The DVP responds to pressure changes much faster than to composition changes. This may cause erroneous readings and sometimes unsteady control (68). Snubbers are therefore often installed in the pressure impulse line (68). Finally, the DVP often has to be located well above the ground, making maintenance and troubleshooting inconvenient. 

OR when the pressure switch impulse line fails dangerously but detected by the effectiveness of the proof test (IMP DU E),... 

The sensor subsystem will also initiate a trip if either of the pressure transmitters (Gate G12) indicates an overpressure. The individual pressure transmitter failures are represented by Gates G18 and G19. G18 indicates that any dangerous failure of a pressure transmitter, its associated impulse line or the associated input circuit of the safety PLC will cause a gate failure. The PFD can be represented by approximate simplified equations. For Gate G18 ... 

Gate 6 accounts for the pressure switch, the impulse line and the connected safety PLC digital input circuit. The simplified approximation for gate 6, PFD is ... 

Valve 4 = Impulse line isolation valve to P/V and N2 regulator... 

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