Control valves location, importance

The type of pump selected for handling oily water has a direct influence on system performance, as do pump control and valve location. The selection of the most suitable pump and control arrangement is therefore of paramount importance. 

A cut-away schematic of a BWR equipped with external coolant pumps is shown in Fig. 17. The recirculation system comprises the external piping, pumps, and valves located at the lower region of the vessel. The penetrations through the bottom of the vessel that contain the control rod drive mechanisms that are vital for controlling the reactivity of the core are not shown in Fig. 17. Of particular importance, as far as the integrity of the reactor is concerned, is the control rod drive tubes and related mechanisms, because they are in contact with the coolant and... 

The location of the reboiler control valve often has a major bearing on the performance, operation, and heat efficiency of the entire column. In an excellent paper, Mathur (280) reviewed pros and cons and several control variations for each location. This review is supplemented and expanded below. The following considerations are important ... 

Plant Lighting The process plant must have sufficient lighting in the important operational areas where control valves, level indicators, and pressure and temperature gauges are located. Good lighting shall also be provided at all escape routes, ladders, work platforms. 

The three valves are all built for chlorine service. Vortex meters upstream of the control valves measure and integrate the various flows. Integration of the flow to the scrubber is the least important, but given the measurement of the flow rate, it is of little added cost. A separate meter located before division of the flow can measure the total flow, or the output of the three individual meters can be added together. The valve positioners may be calibrated for ranges of 15-20 mA (direct user), 9-15 mA (liquefiers), and 4-9 mA (scrubber). The two process valves should have linear characteristics. They should be sized for fiill plant output when 90% open. Normally allowed pressure drops are 5-15 kPa for the direct-use valve and 20-30kPa for the liquefier valve. The scrubber... 

The control strategy, presented in Fig. 11.35, provides smooth transfer with precise control. It must allow controlled venting as well as controlled transfer to compression, and so it requires two control valves and split-range control. The cell room header pressure is measured by a d/p cell with a Monel diaphragm. If desired, a flush-type cell can be used. It is located on top of the header as it leaves the cell room. It is important that connections to the d/p cell be freely draining. 

Dry Air and Nitrogen. Dry air cormections also require special attention. The dry air system exists to serve the dry chlorine end of the process, and so the problem of backflow of process material is always an important one. The connections should be chosen accordingly. In many locations, the design intent will be to have dry air enter part of the chlorine system whenever the pressure falls below a certain level. The natural approach then is to supply pressure regulators. These have the disadvantages already listed. A more secure approach is to use on-off control valves that close whenever the differential pressure across them reverses its direction. 

Important Consideration for Proper Functioning of Control Valves Sensors should be installed at appropriate locations in the process unit (raw material feed lines, in the reactors, or in the product lines) for sensing to detect the actual value of the parameter. 

Figure 12.42 shows an alternative configuration for a flooded condenser. The control valve is located before the condenser. It important that the condensate enters the drum below the liquid level and the equalising line between column and drum is essential. If the... 

In DHRUVA, on-line computation of important physics and process parameters has been achieved. The parameters selected are reactor thermal power, reactivity load due to Xenon, core reactivity balance, heavy water system inventory and performance monitoring of shut-off rods control valve and dump valves. Also off-line application for fuel management, failed fuel detection and location, and stores inventory management have been implemented. 

P IDs (piping and instrumentation diagrams) should identify instruments, sample locations, the presence of sample valves, nozzle blinding, and control points. Of particular importance are the bypasses and alternate feed locations. The isolation valves in these hues may leak and can distort the interpretation of the measurements. 

Understanding the positions of sample and other measurement locations within the equipment is also important. The presence or absence of isolation valves needs to be identified. While isolation valves may be too large for effective sampling, their absence will require that pipe fitters add them such that sample valves can be connected. This must be done in advance of any test. If analysts assume that samples are from a liquid stream when they are vapor or that temperature measurements are within a bed instead of outside it, interpretation of results could be corrupted. Analysts should also develop an understanding of control transmitters and stations. The connection between these two may be difficult to identify at this level in fully computer-controlled units. 

Position indicating instrumentation is used in nuclear facilities to provide remote indication of control rod position with respect to the fully inserted position, and remote indication of the open or shut condition of important valves. This remote indication is necessary for the monitoring of vital components located within inaccessible or remote areas. Remote position indication can be used at any DOE facility, not only nuclear facilities, where valve position indication is required for safety. 

Flumes and (especially) basins have a tendency to leak. A water level controller is important to maintain the water level within a certain tolerance. A point gage and automatic water level float with solenoid valve are configured to turn on a small water supply to keep up with any water losses during the experiments. A tolerance on the water level of 0.6 mm is sufficient to ensure accurate wave measurements. The controller mechanism should be located away from the measurement area to prevent any ripples from the flow of water during or immediately preceding a run. Often, they are turned off during a run to avoid contamination from induced electric currents. 

Any device that controls the amount of light that passes through the device is called a light valve. A device that allows the transmittance to be independently controlled at different locations is called a spatial light modulator (SLM). An important example of such devices is an image projection system. If these projection systems are based on liquid crystals, we call them liquid crystal spatial light modulators (LCSLM). LCSLMs may be electrically controlled by a matrix of pixels or by the intensity of the light incident on the device. 

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