Angle control valve

Per hardware globe control valve (sin e port or double port), rotaiy ecwjtrol valve (ball, plug, or butterfly), angle control valve. 

All three types of valves described above are on-off type devices (binary devices). A basic requirement in the design of these valves is that they offer minimum resistance to flow when open. For many types of calculations it is often justifiable to neglect pressure losses through such devices. But such a simplification cannot be applied to flow control valves. With these devices the control of flow is accomplished either by a constriction or by a diversion. In either case an additional resistance to the flow is introduced. Globe, angle, cross, and needle valves are typical devices of this type. Specific pressure drop correlations should be developed for such devices and used whenever possible. One such correlation used by Stoner (S5) takes the form... 

Fig. 3 Variation in the sample flow rate with the angle of rotation of the sample control valve. The integers within the graph refer to the number of rotations. The y axis is shown on a log scale. The parallel, dashed lines, show the eleven flow rates corresponding to the eleven dilutions...

As mentioned, the flow rate in a standpipe depends on the solid feed device as well as the flow control valve. In this section, we discuss the gas-solid flows in a simple standpipe system where the feed device is a mass flow hopper and the solid flow regulator is a discharge orifice [Chen et al., 1984]. As shown in Fig. 8.15, the entrance of the vertical standpipe is connected to a conical hopper feeder of half angle solids flow patterns are considered. One is a dilute suspension flow, and the other is a solid moving bed. In this case, the following additional assumptions are needed ... 

For housing a petrol gas plant we need only a small room. The gas can be distributed to the practical tables using a 2" main gas pipe with further distributaries of 1/2" pipe. Each practical table is provided with gas taps and these taps should be of the rigid nozzle type and be fitted towards the back of the table. The gas tables be fitted in such a way that the point upwards and are at an angle of 45° from each other. If double benches are provided them taps should be fitted along the centre line of each bench. In most of the laboratories iron pipes are used but it would be preferable, in case of physics laboratory, if we use brass pipes. For controlling the supply of gas in addition to main control valve provision be made to control the supply of gas to each group of tables. These controls should be easily accessible to teacher and should not be easily accessible to students. 

The next level of dynamic testing is with direct sine waves. The input of the plant, which is usually a control valve position or a flow controller setpoint, is varied sinusoidally at a fixed frequency o). After waiting for all transients to die out and for a steady oscillation in the output to be established, the amplitude ratio and phase angle are found by recording input and output data. The data point at this frequency is plotted on a Nyquist, Bode, or Nichols plot. See Fig. I6.3u. Then the frequency is changed to another value, and a new amplitude ratio and a new phase angle are... 

Depending on the bypass flow rate and the minimum flow required, the control valve could be a small rubber-lined butterfly valve or an all polytetrafluoroethylene (PTFE)-lined globe valve. The sizing of this valve can be difficult, because there is very little pressure drop available. Butterfly valves should never be required to control at an open angle of less than 20°. 

The key to solving these problems is to design the vessel for a mass flow pattern. This involves consideration of both the hopper angle and surface finish, the effect of inserts used to introduce gas and control the soHds flow pattern, and sizing the outlet valve to avoid arching and discharge rate limitations. In addition, the gas or Hquid must be injected such that the soHd particles ate uniformly exposed to it, and flow instabiHties such as fluidization in localized regions are avoided. 

Valve Application Technology Functional requirements and the properties of the controlled fluid determine which valve and actuator types are best for a specific apphcation. If demands are modest and no unique valve features are required, the valve-design style selection may be determined solely by cost. If so, general-purpose globe or angle valves provide exceptional value, especially in sizes less than 3-inch NFS and hence are very popular. Beyond type selection, there are many other valve specifications that must be determined properly in order to ultimately yield-improved process control. 

Valves have two main functions in a pipeline to control the amount of flow, or to stop the flow completely. There are many different types but the most commonly used are the gate valve and the globe valve. The gate valve contains a disk that slides at right angles to the flow direction. This type of valve is used primarily for on-off control of a liquid flow. Because small lateral adjustments of the disk cause e.xtreme changes in the flow cross-sectional area, this type of valve is not suitable for adjusting flow rates. 

The effect of a controlled device may not be proportional to its movement. In particular, the shape of valve plugs and the angle of opening of dampers will not give a linear result, and the signal from the controller must take this into account [10, 62]. 

Fig. 8.10. Teflon-glass valves. A number of variants of this basic design are on the market. A "straight through" flow pattern shown here for valve (

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