Single shutdown valve

Figure 12-4 consists of a single Safety Transmitter, safety PLC, and single shutdown valve without tight shutoff requirements with a digital valve positioner. The digital positioner would be provided with the capability for Partial Stroke Testing (PST). 

The pilot gas can be a separate connection or can be connected downstream of the main gas line, depending on the burner capacity. Generally, a single shutdown valve on the pilot gas line is adequate. A pressure regulating valve is also required on the pilot gas line and is generally installed downstream of the shutdown valve. This maintains certain downstream pressure, and no attempts are made to control reboiler temperature while the system is on pilot operation. 

Several steps can be taken to maximize the run time for the reciprocating compressor. Since wear is a function of rubbing speed, the piston speed can be kept to a minimum. Chapter 3 made recommendations for piston speed. Reliability problems due to valves are reputed to account tor 40% of the maintenance cost of the compressor. Valves are the single largest cause for unplanned shutdowns. Basically, valve life can he increased by keeping the speed of the compressor as low as practical. At 360 rpm, the valves are operated six times a second. At 1,200 rpm, ihc valves operate 20 times a second or 1,728,000 times in a day. It is not difficult to understand why the valves are considered critical. To keep the reliability in mind, valve type, material selection and application considerations such as volume ratio, gas corrosiveness, and gas cleanliness need attention by the experts. One final note is that while lubrication is an asset to the rubbing parts, it is not necessarily good for valve reliability. 

The compressors are automatically started and stopped as the load varies. When the total flow can be handled by a single compressor or when any of the surge valves open, FSL-03 triggers the shutdown logic interlock circuit 1 after a time delay. Automatic starting of an additional compressor is also initiated by interlock 1 when PSH-04 signals that one of the compressors has reached full speed. The ratio flow controllers (FFIC-01 and... 

Initiation of shutdown cooling with the most limiting single failure (loss of one shutdown cooling train) can be accomplished via plant procedures using equipment in the operable train (i.e., operating the valves with ( ) for SCS train number 1 or the valves without ( ) for SCS train number 2). 

Large loads can sometimes be best handled with multiple traps in parallel if level control is not justified. Multiple banks of traps for a single load have the advantage that the loss of a single unit does not result in a complete shutdown. One or more of the traps can be valved out of service at reduced loads also. Traps in parallel must be installed in the same horizontal plane. 

Outputs - Typically the outputs are either relays (motor controls) or solenoid-operated valves (SOV). In DTT SIS, the predominant failure mode for these devices is coil "burnout. Redundancy, such as 2oo2 or 2oo3, can be employed on the outputs to prevent a single safe failure of a device or circuit from causing a spurious shutdown. The outputs can also be connected to separate output modules on the logic solver to increase reliability even more. 

Single valve used as safety function Referring to Fig. V11/1.4.T2B, one may note that the control valve is in ON/OFF duty, and in case of emergency, shutdown command will be sent to IVP from safe PLC (SPLC). 

The fast shutdown of the reactor is achieved with a similar system to Winfrlth (ref. 6). Development has revealed that, for the valve size chosen, a capacity several times that required for a single rod Is possible. The larger designs of reactor generally use like... 

For example, a total system shutdown may cause a pump to stop and its discharge valve to close. In the case of a single card shutdown situation, however, it may be that the pump will continue to operate but that its discharge valve will... 

With regard to BWR type reactors, the single risk-dominant initiator is the cold over-pressurisation. There is potential for cold over-pressurisation during filling the reactor at the end of a Shutdown sequence. The status and proper actuation of safety and relief valves were found very important for BWR type reactors during shutdown state. 

For the flame to be effective, it must be oxidizing (represented by a blue flame). Correct flame control is very important. A basic flamer will complete simple work specially designed flame control systems are recommended for routine operations and long production runs. These systems are fitted with gas and air control valves to compensate for pressure fluctuations, ensuring that the mixture is always at its optimum. Safety devices, such as flame failure shutdown, are fitted as standard. Automatic ignition is also standard. Hame nozzle design is important for these normally single or double row... 

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