Low-level trips

Both the high and low level trips cure connected into the IXX Safety Circuit. Any tvo Beckmans in the tripped position will scram the reactor. Interlocks are provided so that bypassing tvo or more Beckmans at the same time will automatically scram the reactor. The BX and BXA relays are time-delayed... 

Check low-level alarms and very low-level tripping device at least once a week. When the water level goes very low, the tripping device shall trip the firing system/hot gases input to the boiler. 

None may bring up the possibility that a pump suction may run dry, damaging the pump, and the recommended action may be to install a low-level trip or alarm (or both) on the vessel from which suction is drawn. 

The flow of fuel to the boiler should have been slopped automatically when the water level fell to a dangerous level. Unfortunately, the low-level trip failed to function. (Many newer boilers come equipped with backup low-level trips.) The operatingengineer investigating this incident determined that this trip had not been tested for years. He set up the following program to prevent a recurrence. First, the fuel gas control valve was locked into its normal operating position with its hand jack. Then the low-liquid-level trip pot (see Fig. 17-1) was blocked in and drained down. Finally, an operator verified that the pneumatic signal to the fuel-gas control valve fell to zero (this valve was AFC—air failure closes). 

Pile period low level trips may be bypassed at start-up, a violation of the operating standard Ihe use of the manual trip at certain reactors is also governed by procedure. 

The sensitrol relay will then drift toward zero, eventually giving a low-level trip. This condition is provided to ensure that the instrument cannot be made inoperative during the operation of the reactor. The same is true for the CPM-Meter-H.V. switch if the switch is turned to the H.V. position, the low-level scram will occur on Channel 1. The output of the count rate is fed to a Varian recorder and the corresponding sensitrol relay of the channel. 

A furnace was protected by a relief valve on its inlet line (Figure 10-1). A restriction developed after the furnace. The relief valve lifted and took most of the flow. The flow through the furnace tubes fell to such a low level that they overheated and burst. The low-flow trip, which should have isolated the fuel supply to the furnace when the flow fell to a low value, could not do so because the flow through it was normal. 

The smaller of the two boilers became short of water first, and the low w ater level trip shut it dowm. The operator was so busy trying to get it back on line that he ignored the low water level and other alarms that were sounding on the other boiler. Unfortunately the trips on this boiler did not work, as it had been rewired (incorrectly) since it was last checked. Fifteen to 20 minutes later, someone saw flames corning out of the boiler stack. The boiler was then shut down manually. By this time most of the tubes had melted. 

Ionization smoke detectors contain a small radioactive source (Americium 241) which ionizes air in a small chamber. The ions flow to a charged plate giving a measurable current. Products of combustion in the chamber are not easily ionized and absorb the radiation and reduce the current. The low current trips the alarm circuit. The size and composition of the particles are crucial to successful detection so that some types of smoke or vapor are detected at very low (invisible) levels. 

A less common type of fuel-gas trip to a heater is a low-pressure trip. A pressure transducer generates a milliamp output from a boiler feed-water pump. Should this milliamp output fall below a certain level, the... 

Compressors are also served by high-liquid-level trips in their upstream knockout drums. These high-liquid-level trips work in the same way as the low-level boiler trips discussed above, except that the mercuroid switch is activated by a rising, rather than a falling, liquid level so as to protect the compressor from a slug of liquid. 

Aqueous trip blanks sometimes accompany soil samples collected into metal liners or glass jars. In this capacity they do not provide any meaningful information. Soil samples do not have the same contamination pathway as water samples because they are not collected in 40-milliliter (ml) VOA vials with PTFE-lined septum caps. In addition, soil does not have the same VOC transport mechanism as water does (adsorption in soil versus dissolution in water). There are other differences that do not permit this comparison different sample handling in the laboratory different analytical techniques used for soil and water analysis and the differences in soil and water MDLs. That is why the comparison of low-level VOC concentrations in water to VOC concentrations in soil is never conclusive. 

Collect trip blanks for water sample analysis only when low level contamination is a matter of concern. 

A safety trip can be incorporated in a control loop, as shown in Figure 5.29a. In this system the level control instrument has a built-in software alarm that alerts the operator if the level is too low and a programmed trip set for a level somewhat lower than the alarm level. However, the safe operation of such a system will be dependent on the reliability of the control equipment, and for potentially hazardous situations it is better practice to specify a separate trip system, such as that shown in Figure 5.29b, in which the trip is activated by a separate low-level switch. Provision must be made for the periodic checking of the trip system to ensure that the system operates when needed. 

Analyses for "copper, cadmium, and lead were carried out continually by DPASV. Zinc determinations were excluded to permit use of a lower electrolysis potential. The samples were analyzed at pH 4.9 by sparging with carbon dioxide. An 8-min. electrolysis at —1.0 V vs. silver/ silver chloride and a 25-mV pulse were used during the Seattle-Saanich portion of the trip (Leg 1) while a 10-min. electrolysis and a 50-mV pulse were used from Saanich to Seattle (Leg 2). Application of the DPASV technique resulted in greater sensitivity and thus shorter plating times for the low levels encountered. It also afforded better resolution for "copper than linear-sweep ASV. It should be pointed out, however, that DPASV does not result in shorter analyses times because the stripping portion of the analysis is very slow. Nevertheless, it is worthwhile to limit the time of electrolysis because this also reduces the concentrations of interfering metals accumulated in the mercury fllm. Under the... 

When a low level can cause such hazards, it is a good practice to install low-level alarms or trips. The trips usually cut the bottom flow rate, or introduce a diluent into the bottom sump. 

As with column bottom level, when an excessively high or low level can be hazardous, it is a good practice to install high-reliability level instrumentation including alarms, trips, and indicators, and to mount these as per Figs. 5.4 and 15.16. The trips usually switch off rotating machinery downstream of the accumulator and/or cut off product flow. 

Using a single sensor for both the BPCS and SIS requires further review and analysis. The additional review and analysis is necessary because a failure of this single sensor could result In a hazardous situation. For example, a single level sensor used for both the BPCS and a SIS high level trip could create a demand if the sensor fails low (i.e., below the set point of the level controller). As a result of the sensor failing low, the controller would drive the valve open. Since the same sensor is used for the SIS, then it will not detect the resultant high level condition. 

Safety interlocks provided (high steam pressure and low water level trip) ... 

Low water level in waste Chance of leak of water tubes of boiler Automatic level controller and audio Air blower and sulphur pump should trip at very low level of water... 

Water level indicators and control being offered by vendor (There should be two level gauges with isolating valves, and alarms for low and very low water levels with auxiliary contacts for tripping the firing in case of the very low level). 

The RPV control EOF is designed to maintain adequate core cooling, shutdown of the reactor, and decrease RPV temperature to cold shutdown conditions. Entry into this procedure is required at an RPV water level below (low level scram set point), RPV pressure above (high pressure scram set point), drywell pressure above (high pressure scram set point), and SCRAM condition and reactor power above a certain value (average power range monitor downscale trip) or reactor power cannot be determined. 

Medium (M) Acceptable with further risk reduction One monitoring device with SIL or of high quality (documented testing) or administrative procedure of high quality (e.g., tripping of large pump from low level of suction sump). 

Two independent low water level trips provided for unattended boilers... 

There are commercial units, some in the NIM format, for monitoring the level of nitrogen in the Dewar. These can give audible or visual warnings of a low level and can be arranged to trip out the HV and/or initiate an automatic nitrogen fill cycle. 

Cross-check gauge glass level with control room level Drain low-liquid-level trip pot to lest... 

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