Closed valve shutdown valves

Low demand mode Where safety function is only performed on demand to transfer equipment under control (EUC) into a specified safe state and the frequency of demand is less than one per year. Fig. VII/1.4-1 is an example of demand mode of operation. This is because normally the level in the tank will be maintained by sensors Sn and control valve Cy, but in case of a high level to avoid a hazardous situation, separate protection sensors will come into play and close the shutdown valve Sy. So safety comes on demand. 

In recent years much more attention has been given to pipeline isolation, after instances in which the contents of export pipelines fed platform fires, adding significantly to damage and loss of life. Many export and in field pipelines are now fitted with emergency shutdown valves (ESDV) close to the production platform, to isolate the pipeline in the event of an emergency. 

There are three basic requirements that Hquid level control devices are designed to satisfy alarm functions, pump/valve control, and transmitted output signal to track level continuously. Alarm devices provide warning or shutdown functions when process levels pass a predeterrnined point in the vessel pump /valve control devices turn on/off pumps or open/close valves at predeterrnined levels in the vessel and transmitters provide a proportional output signal over a predetermined span to send to a local meter or signal back to a control room. 

The operation of system valves (also starting and shutdown of pumps) has a significant effect on the transient fluid pressures in the piping system because of the acceleration and deceleration of the fluid as it changes its velocity. As a simple example, the maximum head rise caused by the instantaneous closing of a valve is given by... 

The expander is now ready to be put into operation. Open the compressor inlet valve and expander discharge valve simultaneously. Then open the compressor discharge valve. Make sure the variable nozzles are in the closed position. Push the start button on the control panel to open the inlet shutdown valve. 

Car-Sealed Closed Valve - In certain cases it may be advantageous to use car sealed closed valves, such as in a bypass around a fuel gas control valve used for furnace flameout protection. The bypass is provided so that the automatic shutdown system can be periodically checked for operation. Where CSC valves are used for other purposes, they are also limited to appUcations where inadvertent opening of the CSC valve would not overpressure the equipment by more than 1.5 times design pressure. 

Valve Arrangement of Auxiliary Feedwater System and Main Steam System during Shutdown - the auxiliary feedwater system has six MO Vs in the flow path to the steam generators and the main steam nonreturn valves are normally closed during shutdown. These valves depend on offsite power and are difficult to manually open. 

After an activation period of 4 h, the conversion showed a maximum of 40% followed by a steady decrease in conversion (Figure 4.38). Overnight, the pressure was decreased to 6 MPa and the needle valve on the permeate side was closed. This shutdown procedure caused the catalyst to precipitate and no reaction occurred anymore. The precipitated catalyst can be used for a new cycle by pressurization of the membrane reactor, redissolving the catalyst. At the end of the third run the conversion had dropped to 33%. A TON of 1.2xl05 in 32 h (t 62 min) was obtained. ICP-AAS analysis of the permeate stream indicated complete retention of the catalyst. The authors propose possible traces of oxygen as the cause of the decrease in activity of the catalyst. 

Technology—Designs that have a detrimental affect on performance include a piece of equipment meant to be used outdoors designed with data entry keys that are too small and close together to be operated by a gloved hand, or a shutdown valve positioned out of easy reach. 

Safety shutdown valves, which are normally wide open and operate infrequently, are expected to respond to a safety trip command reliably and without fault. To achieve the level of reliability required in this application, the safety valve must be periodically tested to ensure positive operation under safety trip conditions. To test the operation of the shutdown system without disturbing the process, the traditional method is to physically lock the valve stem in the wide-open position and then to electrically operate the pneumatic shutdown solenoid valve. Observing that the pneumatic solenoid valve has properly vented the actuator pressure to zero, the actuator is seen as capable of applying sufficient spring force to close the valve, and a positive safety valve test is indicated. The... 

The effect of this on the reactor operation would have to be considered. This would be brought out in the operability study on the reactor it would be a possible cause of no chlorine flow. Since the flow controller does not know that steam flow has been lost, chlorine will continue to be pumped into the vessel until the high-level alarm sounds and the high-level shutdown closes the control valve. A secondary consequence is that the vessel is now filled with liquid chlorine that must be drained to a safe level before operation can be resumed. The operating procedures must include instructions on how to deal with this scenario. 

When started, the rotary pump carmot generate an underpressure to suck in the liquid to be pumped, and the suction pipe and the pump must therefore be filled with liquid. Hence, startup and shutdown are carried out in situ against the closed valve on the pressure side. For reasons of availability, generally two pumps are combined to give a pumping station (Figure 2.4-5). 

Eight minutes after SG shutdown, water valves at the module inlet were closed, while outlet valves were closed in ten minutes. Then steam replacement with nitrogen was initiated. 

High pressure possibly due to closing of a separator inlet shutdown valve (SDV) or other block valves, improper setting or failure of the choke, or blocking in of a section of line. 

Condenser solvent-locked because valve in reflux return line was closed following shutdown for maintenance 3... 

Engineers select and evaluate process equipment. The selected equipment must be technically sound, rehable, safe and easy to operate, serviceable, economically attractive and environmentally sound, e.g. minimal noise pollution and no mechanical and fire hazards. For example, all pneumatic valves, except for the modulating valves, are air-to-open/ spring-to-close valve type for safe shutdown unless the valve is a divert drain valve as... 

The valve in the gas line behind the knockout pot shuts down the vaporizer when any of several hazardous events occur. The valve prevents too high a flow of gas, which should not be allowed to exceed the vaporizing capacity. This would lead to entrainment of liquid chlorine. The valve also can respond to a loss of energy input due to failure of the heating medium. With such functions, the valve should close upon loss of signal. It may also be useful to have a pressure-reducing valve in the line to stabilize the downstream pressure and incidentally to develop some superheat in the gas. When fitted with an actuator, this can also serve as the shutdown valve. 

Shutdown basically follows the reverse procedure stop pump, open recycle, close block valve, check valves with ammonia, check nitrogen seal system (which should remain in operation even when no transfer is being made). 

Two poison tanks which contain highly borated water (12,000 ppm of boron concentration) are installed in the CV for the passive reactor shutdown system (PRSS). Each poison tank (60 m ) is connected to the RPV by two pipes. The upper pipe has two normally closed hydraulic pressure valves. The pressure in the poison tank is maintained to be equal to that of the primary system under normal operation. The borated water in the tank is cooled by the C V water. The inside wall and the nozzle part of the poison tank have liners for mitigating a thermal stress due to temperature change during poison injection. 

Administrative control failures include deviation from standard operating procedures, failure to close valves, failure to activate the emergency shutdown system, and failure to activate the BOP. Administrative controls are subject to failure when procedures have not been adequately developed, implemented, audited, and enforced. 

The letdown flow outside containment isolation valve is a normally closed, fail closed, air-operated globe valve that isolates letdown to the liquid radwaste system. This valve automatically opens and closes on a plant control system signal from the pressuriser level control system or a containment isolation signal from the protection and safety monitoring system. Ibis valve operates in the same fashion as the letdown flow inside containment isolation valve. The letdown flow outside containment isolation valve eloses more quickly than inside containment letdown flow isolation valve to limit seat wear of inside containment isolation valve. This valve operator has a flow restricting orifice in the air line, so it opens more slowly than inside containment letdown flow isolation valve. In addition, during brief periods of shutdown, when the reactor coolant system is water solid, this valve throttles to maintain the reactor coolant system pressure. Manual control is also provided in the main control room and at the remote shutdown workstation. 

Automatic opening of the motor-operated valve of the in-containment refuelling water storage tank injection line occurs on a low hot leg water level signal. These valves are closed during shutdown conditions, such as mid-loop and vessel-flange operation, when the reactor coolant system is at atmospheric pressure. This also reduces the importance of operator action on these events. 

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