Low-pressure trips

Option 4 Pressure switches are required for low pressure trip, alarm, and aux. pump start... 

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... 

Low-pressure trip This is used for probable major subsea leakages indicated by sudden pressure drop. 

The minimum alarms and trips reeommended for eaeh major driver and driven maehine should be a low oil pressure alarm, a low oil pressure trip (at some point lower than the alarm point), a low oil level alarm (reservoir), a high oil filter differential pressure alarm, a high bearing metal temperature alarm, and a metal ehip deteetor. See Table 15-1. 

It should be emphasized at this point that the speed of response is cnti-cal. The pressure transient pressure should not fall to less than 50% of the difference in pressure between the standby pump start pressure and the low oil pressure trip pressure. This is normally achievable with good design practice and the use of a switch and direct wiring. There is some tendency to use a transmitter and control through a remote computer. The latter arrangement is difficult to check on a shop test and normally is too slow to meet the requirement. An accumulator can be added and must be used if the requirement cannot be met. This additional hardware contributes to higher initial cost and possible reliability problems in the future. The direct switch method is therefore highly recommended. 

The tank should be placed at an elevation that provides a static head less than the low oil pressure trip switch setting so as to not interfere v illi the normal trip function. Normally this means that the static head should not be more than the equivalent of 5 psi. The minimum sizing should he based on a three-minute rundown cycle. Adding a bit more to the time is probably not all that costly. 

An alarm shower can occur when high pressure in the reactor trips the feed by closing a valve and turning off the feed pump. In addition to the high pressure trip alarm, the operator is frequently showered with low feed flow, low-low feed flow, and feed pump off alarms. 

With alarm management, the high pressure trip would alarm, but the other associated alarms would be suppressed, since they are the expected result of the high pressure trip. On the other hand, a low flow condition from a different cause would be alarmed. Plants with managed alarms are inherently safer than those without since it is easy to silence and overlook a critical alarm in the midst of an alarm shower. However, the benefits should be balanced with the increased complexity and maintenance requirements. 

The pressure drop in the pipeline should be measured, and if it gets too low, a trip valve should be closed automatically. A very reliable, duplicated system may be necessary [16]. 

On the boiler that exploded the manual individual burner valves were not closed when the boiler shut down. After the purge period, fuel gas was admitted to the header from remote manual controls in the control room and into the firebox. Low fuel gas pressure tripped the master safety valve after each attempt to pressure the fuel header. Three attempts were made to purge the boiler and on each of these occasions fuel gas was dumped into the furnace through the open manual burner gas valves. On the third attempt a severe explosion occurred. 

Safety features such as overspeed trip, low oil pressure trip, remote solenoid trip, vibration monitor, or other... 

Test results ( , ) for several candidate materiaIs (Table III) are reported which span the range of energetic capacity. Those values which exceed the threshold are highly susoect and have been known to result in serious fires in the past. Mix No. 1, (M49A1, Trip Flare Mixture) is a "safe" mixture that is insensitive to electrical spark, impact, and friction. It does not have a fast bum rate on the Vee Block tester and it has a low pressure-rate-of-rise. 

Pressure differential indicator 15. Low pressure switch (trip)... 

Some heaters also have a low fuel-gas pressure trip on the fuel gas itself. The idea here is that if fuel-gas flow is lost, we do not want it to surge back into the heater too quickly, if it is suddenly restored. 

The primary system is intended to isolate the major equipment in order to prevent reverse flow and exhaust oxides in a gaseous state. It consists of a special restraint type valve (check) and two motorised shutdown valves, arranged in series. The system includes a low pressure detector on the main pipe that trips the sulphuric acid pumps, isolates the process and stops the helium flow into the reactor and heaters (emergency system EAS-200). 

The electrical support for this system is the emergency generator for the section of sulphuric acid decomposition. The pressure detectors PI201 and PI202 trip the system on low pressure. The diagram of the primary system is shown in Figure 3. 

Figure 5.2 is an illustration of a vessel double-wall containment system. The annular space is kept at a higher pressure than the tank. Should a leak develop, the pressure in the annular space will fall because the flow capacity of the nitrogen pressure control system has been limited. A low pressure will occur, tripping a pressure alarm low (PAL), and alerting the operator to the leak. 

Unfortunately the temporary filter was placed between the compressor and a low suction pressure trip. The compressor suction pressure was reduced to a vacuum and air intruded into the system. The air reacted within the system. A decomposition occurred further downstream and a major fire caused many months delay in the startup of this unit. 

The exhaust from the low pressure turbine cylinders flows to the main turbine condenser which has three shells, located under the exhaust hoods of the low pressure turbine cylinders. The condenser is designed to accept also the steam flow from the main steam bypass system on startup, hot standby and turbine trip. During normal power operation, the steam flow to the condenser amounts to about 60% of the total steam flow, but the condenser system is designed to accommodate the full steam flow for a limited time period the steam flow shall be reduced to 60% within 20 seconds to avoid a reactor trip due to too high condenser pressure. 

The condenser is cooled by the circulating water system which typically incorporates three electrically driven pumps loss of one pump will call for a power reduction, but will not yield a turbine trip in the short term. The condensate is pumped forward to the dearator (or the feedwater tank) through low pressure heaters and a condensate cleanup system with ion exchange filters by means of three 50% condensate pumps. The drmnage from the heaters is pumped forward through the cleanup system by means of a dedicated low pressure drain pump. 

The turbine exhaust flows to a condenser which has three shells, located under the low pressure turbine exhaust hoods. The condenser also accepts the exhaust flow from the feed pump turbines and, on startup, hot standby and turbine trip, flow from the main steam and bypass system. 

Both PIMl-COl-40 and PIM demonstrate high N2 uptake at extremely low pressure with hysteresis, which may be an indication of the microporous nature. Trip(R)-PIMs exert surface areas in the range of 618 m (when R = octyl) to 1760 m g (when R = methyl). Flexible, linear side chains occupy larger volume than branched ones. That is why higher surface area is observed with branched alkyl-derived PIMs than their linear chain derivatives. Polyimide-linked PIMs have BET surface areas in the range of 471-683 m g ... 

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