Shut-down circuits

Trips should deenergize circuits and not require the shutoff/shut-down circuit to energize. Process creep can be documented by... 

Direct expansion is also possible wherein the refrigerant is used to chill the incoming air directly without the chilled water circuit. Ammonia, which is an excellent refrigerant, is used in this sort of application. Special alarm systems would have to be utilized to detect the loss of the refrigerant into the combustion air and to shut down and evacuate the refrigeration system. 

A pressure switch located so as to sense falling pressure at the earliest moment should be used to activate the standby pump. The switch should be so connected to the system as to permit testing the startup circuit without shutting down the compressor. Figure 8-8 shows four piping arrangements. The figure at b would be the recommended method. 

Provision must be made in the wiring to maintain power to the standby pump driver. This will prevent power interruption due to the pressure switch contacts opening when lubricant pressure is restored. Cycling of the standby pump will occur if the circuit is not maintained. A reset will have to be furnished to permit shutting down the standby pump when the main pump is back on stream. 

Combustible gas detection systems are frequently used in areas of poor ventilation. By the early detection of combustible gas releases before ignitible concentration levels occur, corrective procedures such as shutting down equipment, deactivating electrical circuits and activating ventilation fans can be implemented prior to fire or explosion. Combustible gas detectors are also used to substantiate adequate ventilation. Most combustible gas detection systems, although responsive to a wide range of combustible gases and vapors, are normally calibrated specifically to indicate concentrations of methane since most natural gas is comprised primarily of methane. 

Many systems are shut down for periods of the year, either for process closure or if not required in winter. The advice of the supplier should be sought as to the correct procedure. In the case of refrigerant circuits, it is advisable to pump down into the receiver or condenser to minimize leakage losses. Water towers should be drained in winter in this climate, if not in use, and the tank heater disconnected. 

Under no circumstances should refrigerant be added to a leaking circuit without first making a repair. The one exception to this rule may be a continuous process plant, where the cost of a shut-down may override the cost and inherent danger of a small continuous leak. 

FET is ihe on-off current ratio, which indicates its ability to shut down the current, and is particularly relevant in applications such as active matrix displays and logical circuits. Because of the presence of p-n junctions at both the source and drain electrode, the on-off ratio of MOSFETs is in the I0y range [12J, while that of a-Si H TFT is limited to 106 [13], High mobility ensures high on-current and, hence, also contributes to a high on-off ratio. 

Fourthly, intrinsically safe electrical circuits are the easiest to maintain. Since intrinsically safe circuits by their nature are incapable of causing ignition, they can be maintained without regard to shutting down operations, nor are hot permits required, or is lengthly disassembly, assembly and recertification of added protection required. 

On confirmed gas detection sources of ignition such as welding or small power circuits should be immediately shut down in the affected area (immediately shut down is applied to equipment not rated for use where hazardous gases are present). 

Improved next-generation ODC with a catalyst based on rhodium [6] promises an even more simplified plant concept. This is due to the fact that this type of ODC does not require polarisation during shut-down as an inert cathode is no longer necessary. The plant can simply be put at stand-by where the anode side, as well as the HC1 circuit, remains pressurised under chlorine saturation. Therefore, re-starting the operation is very simple and the chlorine supply is derived directly from the electrolysis and liquid chlorine evaporation is no longer necessary. Instead, with a liquid chlorine buffer, the system can be re-started from the hydrochloric acid storage tank. 

The results of the calculations reveal that the Ru losses from erosion, dissolution and open circuit corrosion (assuming shut-downs at a frequency of 12 per year), occurring... 

Stable for 5000 h for automotive and 40 000 h for stationary applications under operating conditions as well as open circuit and shut down conditions. 

The initial incident involved a pinhole leak on a 6-in. line located 112 feet above grade. The unit might have been shut down at this point, but a decision was made to keep it on line. Efforts to isolate the circuit by closing four block valves failed. The line remained hot and the level in the downstream stripper vessel continued to rise. Several attempts were made to depressure the circuit and free drain all the residual naphtha. At least 15 work orders were issued over a 13-day period and most of these failed to meet the company s own work standards. 

A latching circuit waits for an event to occur. Once that event occurs, the latch output changes state and will ignore any further events until reset. This can be described as a memory element. The latch has many applications in the system. For example, if a failure mode occurs in the system, a shutdown signal may be sent to the latch circuit, which will shut down the system and prevent any further possible damage. The system will remain shut down until the power to the system is recycled. 

The most outstanding source of instability, which from an academic point of view may be difficult to realize, is the corrosion that can arise at open circuit when a cell is shut down for maintenance or other reasons [108]. The cathode can simply corrode, or can be oxidized. In the latter case, the residual oxide can be deleterious for the catalytic activity since it may remain unreduced even under cathodic load. Therefore, cathode materials usually contain additives whose function is to reduce the consequences of shut-downs [109]. Laboratory experiments should thus include also this kind of test if a complete analysis of the material is to be done [105, 108, 110]. If the cathode corrodes, some cathodic protection may need to be maintained during shut-downs [7], which is of course to be accounted for in the evaluation of the economic efficiency. 

An AFC combined with a lead acid battery has been used in a hybrid vehicle. Between operating times the cell was shut down by using the battery to drain the KOH electrolyte. This technique can improve the life expectancy enormously by protecting the fuel cell from a high open circuit voltage, which otherwise could induce carbon oxidation processes to produce carbonates that would destroy the matrix electrolyte. 

Should an emergency occur requiring immediate shutdown and over-ride of normal sequenhal shutdown, an EMERGENCY STOP pushbutton is provided for this purpose. This device interrupts power to all components in the oxidation unit control circuit, shuts down all motors, and closes the vacuum line valve and the chlorine pressure-reducing valve (PRV). The EMERGENCY STOP pushbutton is also used as a reset device to restore the system to normal operating status after an alarm situation has occurred. 

One way to do this is to use pressurized enclosures for electrical components. They maintain a slightly higher pressure inside than the atmosphere outside them, so if a leak does occur in the enclosure, it will vent outward and will not allow a flammable hydrogen and air mixture to go inside. If the pressure inside falls below a certain point, an alert occurs and the system is shut down. This can be done in different ways depending on the circumstances. Most systems have an audio alert as well as a visual indicator such as a blinking LED. In addition to this, upon loss of pressure a circuit will immediately disengage the power supply to any circuits and electrical devices within the enclosure, and the system will be shut down automatically. If you have an experimental device that is constantly attended while in the operation, a simple cutoff switch that is operator activated and approved for hazardous atmospheres will suffice. 

The catalyst should also be resistant to thermal shock, that is, a sudden increase or decrease in temperature. Rapid temperature changes occur during start-up or shut-down of the turbine. The most serious thermal shocks occur upon sudden loss of the turbine load. If the turbine load is lost (by opening a circuit breaker, for example) the fuel must be shut off immediately to prevent overspeeding and destruction of the turbine. The air continues to flow, however, so the temperatme of the catalyst drops very rapidly. Under these conditions the catalyst temperature can fall 1000°C in 100ms, which poses severe problems for ceramic materials. Most... 

It is valuable to provide connections on the cooling water system, that may be used for flushing to dislodge any accumulations of deposits that might occur. The opportunity to isolate heat exchangers by the inclusion of bypass systems, must be included so that off-line cleaning can be carried out without the need to shut down whole sections of the total cooling water circuit. 

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