Valve authority

The ratio between the pressure drop through the open valve and the total pressitre drop can be expressed by the valve authority ... 

Car Seal A metal or plastie eable used to fix a valve in the open position (ear seal open) or elosed position (ear seal elosed). Proper authorization, eontrolled via administrative proeedures, must be obtained before operating the valve. The physieal seal should have suitable meehanieal strength to prevent unauthorized valve operation. 

In recent years new ec]uipment has been invented, chemical processes, piping materials, valve designs, and new teehnologies not eonsidered when these formulas were developed with eold water in the 19th century. There is a need to measure the aetual losses onee an industrial plant is eommissioned and operations begin. I he authors of this book have developed a formula that permits the measurements of these losses in a live functioning system. Here it is ... 

Another pressure control method is a hot gas bypass. The author has seen a retrofitted hot gas bypass system solve an unsatisfactory pressure control scheme. In the faulty system, a pressure control valve was placed between the overhead condenser and the lower reflux drum. This produced en atic reflux drum pressures. A pressure safety valve (psv) vented the reflux drum to the flare to protect against over-pressure. A psv saver control valve, set slightly below the psv relieving... 

Limit access to storage areas to authorized staff knowledgeable in the hazards, position of valves and switches. 

All companies keep a register of relief valves. They test them at regular intervals (every one or two years) and do not allow their sizes to be changed without proper calculation and authorization. 

Multidimensional LC has also been used to determine ursodeoxycholic acid and its conjugates in serum (14). These compounds are used in the treatment of cholesterol gallstones, hepatitis and bilary cirrhosis. These authors employed a traditional (10 X 4 mm) pre-column and a micro-bore (35 X 2 mm) analytical column that were interfaced by using a six-port switching valve. 

Figure 2-20 Eauivalent length resistance of valves and fittings to flow of fluids. Note apply to 2 in. and smaller threaded pipe for process applications (this author). By permission, Crane Co., Technical Paper 409, Engineering Div., 1942, also see [3].

Figure 7- l4. Safety valve design operational check sheet. Adapted and added to by permission, N. E. Syivander and D. L. Kiatz, Design and Construction of Pressure Relieving Systems, Univ. of Michigan Press, Ann Arbor (1948). Six items of overpressure list above by this author and from API Rec. Practice 521 (1982). 

The API-RP-520 [10] recommends calculating the amount of vapor flashed and the amount of residual liquid (unfiashed) and then sizing valve orifices for each condition. Select a valve (s) area that has a total area at least equal to the sum of these two areas. Before settling for this approach, this author recommends examining... 

To pro dde some external protection against the damage that an external lire can do to a pressure relief valve or rupture disk, this author recommends that these devices be insulated after installation in such a manner as not to restrict their action but to provide some measure of reliable performance, even if the vessel is not insulated. 

Kister et al. [136] prepared one of the few comprehensive distillation studies for the application selection of valve and sieve trays compared to random or structured packing. This reference is based on a more comprehensive evaluation of accumulated data by the same authors [137]. Many separate studies have been conducted for trays [138] including bubble caps as well as various packings, but few, if any attempt to establish similar conditions to make a viable comparison as is attempted in References 136, 137. There are four main differences related to capacity and separation [136] when considering ... 

The checking and readjustment as necessary of all safety controls is an essential part of periodic maintenance - possibly annually. A time should be chosen when temporary stoppage of the plant will not cause inconvenience. Unsafe conditions can be set up by throtding valves, stopping pumps, or removing the load. In each case the relevant safety control should function at the pre-set conditions. Safety checks on specialized items such as fire dampers may be required from time to time by local authorities, and these checks, together with the expert advice available from the testing officers, should be welcomed as proof of the inherent safety of the installation. 

Fig. 11. Schematic of a research flow-reversal reactor showing switching valves and instrumentation. Heavy insulation was used to tty to obtain adiabatic operation. (Figure adapted from Xiao and Yuan, 1996, with permission of the authors.)...

Nolte (1978) gives detailed methods for the selection of economic pipe diameters, taking into account all the factors involved. He gives equations for liquids, gases, steam and two-phase systems. He includes in his method an allowance for the pressure drop due to fittings and valves, which was neglected in the development of equation 5.12, and by most other authors. 

XPS has been used by several authors to identify the surface and bulk composition of ruthenium based, valve metal stabilized DSA electrodes for chlorine evolution. Augustynski et al. [45] investigated the composition of Ru02-Ti02 electrodes before and after electrochemical treatment. They found a surface composition which deviated significantly from that of the bulk. The Ru/Ti ratio corresponded to 0.15 at the surface while in the bulk 0.28 was measured. Similar results were obtained by De Battisti et al. [46] for Ru02-Ti02 electrodes with different composition ratios on Ti substrates. Fig. 10 shows the Ru/Ti ratio for different solution compositions as a function of the depth. 

When the oxide is formed by anodizing in acid solutions and the sample is then left to rest at the OCP, some dissolution can occur. This process has been studied by a numbers of authors,70-75 especially in relation to porous oxides [cf. Section 111(4)]. It was found that pore walls are attacked, so that they are widened and tapered to a trumpet-like shape.70 71 Finally, the pore skeleton collapses and dissolves, at the outer oxide region. The outer regions of the oxide body dissolve at higher rates than the inner ones.9,19 The same is true for dissolution of other anodic oxides of valve metals.76 This thickness dependence is interpreted in terms of a depth-dependent vacancy concentration in the oxide75 or by acid permeation through cell walls by intercrystalline diffusion, disaggregating the microcrystallites of y-alumina.4... 

Sampling for gas phase chromatographic analysis can be readily achieved by a grease-free, rotatable, multiple-ported gas sampling valve. Various commercial units of this sort are available. However, the author s laboratory preferred to fabricate to its own design (Y. Shimoyama, 1970) the result is a valve containing only stainless steel and PTFE and specifications... 

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. 

Lock the stop valve in the open position. Instruct authorized personnel of the importance of not inadvertently leaving the stop valve closed and of being present during the entire period that the stop valve is closed so that they can lock it in the open position before they leave the location. 

Sectionalizing valves may be installed above ground, in a vault, or buried. In all installations, an operating device to open or close the valve shall be readily accessible to authorized persons. All valves shall be suitably supported to prevent settlement or movement of the attached piping. 

If stop valves are located in pressure relief piping, and if any of these stop valves are to be closed while the equipment is in operation, an authorized person should be present. The authorized person should remain in attendance at a location where the operating pressure can be observed and should have access to means for... 

As described above, a lockout device can be used as a security measure to prevent unauthorized access to aboveground valves located within chemical processing systems. Valve lockout devices are locks that are specially designed to fit over valves and valve handles to control their ability to be turned or seated. These devices can be used to lock the valve into the desired position. Once the valve is locked, it cannot be turned unless the locking device is unlocked or removed by an authorized individual. 

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