Control valve station

Bypass valves are sometimes installed to allow the control valve to be repaired without shutting in production. On large, important streams the bypass could be another control valve station. Manual bypass valves are... 

Control valve stations should be designed considering the following ... 

The control valve station should be located to facilitate operation and maintenance. 

Control valve stations are preferably located at grade for the inline unit and at main operating levels for the vertical arrangement. It is not absolutely necessary to locate control valve stations in such a way that pneumatic or electrical interconiieaions are kept to a... 

In addition to energy conservation, the variable speed drives offer better control because of a faster response, ie, reduced dead band. They are also sometimes chosen for safety reasons because of elimination of the control station and accompanying valving. The capital saved by use of a smaller motor and elimination of the control valve partially compensates for the cost of the drive. 

Whenever it is necessary to control the process level, pressure, temperature, etc., a control station is installed. A control station may be as simple as a single control valve or it may contain several control vahes, block valves, bypass valves, check valves, and drain or vent valves. 

The piping around any facility, other than the straight pipe connecting the equipment, is made up primarily of a series of control stations. Flow from one vessel goes through a control station and into a piece of pipe that goe.s to another vessel. In addition to considering the use of block valves, check valves, etc., all control stations should be designed so that the control valve can be removed and any bypass valve is located above or on a level with the main control valve. If the bypass is below the con tiol valve, it provides a dead space for water accumulation and corrosion. 

The downstream pressure-sensing pipe of each valve is connected to a straight section of pipe 10 diameters or 1 meter downstream of the nearest tee, elbow or valve. This sensing line should be pitched down, to drain into the low-pressure line. If it cannot drain when connected to the top of this line it can often be connected instead to the side of the pipe. The pipe between the two control valves must be drained through a steam trap, just as would the foot of any riser downstream of the pressure-reducing station. 

There must be a master control valve or switch accessible to and within 15 feet of the instructor s station for emergency cut-off of all gas cocks, compressed air valves, water, or electrical services accessible to students. Valves must completely shut-off with a one-quarter turn. This master control is in addition to the regular main gas supply cut-off, and the main supply cut-off must be shut down upon activation of the fire alarm system. 

The objective is to have the vacuum surge tank as close as possible to the forming station and the vacuum control valve. Use of flexible vacuum hose with connections eliminates elbows, tees, and tubing reducers. All valves must be capable of operation at the full open position. To utilize fully the rapid vacuum capability provided by the surge tank, the mold must be able to take advantage of all vacuum pressure available. Vacuum holes should be drilled as large as possible, and a maximum number should be used. 

The pressure control signal acts along with the signal from a transfer loading station to operate the two control valves. This is the method described in Fig. 11.35. The particular combination shown in Fig. 11.37 is appropriate for positive header pressures of about 15-35 kPa. The set points used in Figs. 11.20 and 11.38 are arbitrarily chosen near the maximum in this range and do not represent any particular electrolyzer technology. 

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Reactor pressure increase Several events may cause this e.g., inadvertent closure of one turbine control valve, pressure regulator downscale failure, generator load rejection, turbine trip MSIV closure, loss of condenser vacuum, loss of nonemergency AC power to station auxiliaries, loss of feedwater etc. All these have been analysed. Features are included in the instrumentation and control systems or redundancies to maintain reactor pressure through a combination of component automatic responses or operator actions, depending on the identified cause. 

Installation of a position indicator of the control valve of the steam line in the measurement control station. 

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