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Vacuum Materials, Hardware, Fabrication Techniques, Cleaning Processes and Surface Treatment
Published in Pramod K. Naik, Vacuum, 2018
Vacuum valves are integral components of vacuum system as they provide necessary control for the flow of gas. The valves can be used for isolating different parts of the vacuum system. Different types of vacuum valves are selected depending upon the application. Valves can be manually operated, solenoid operated, electro-pneumatically operated or hydraulically operated. A needle valve, used for introducing controlled leak of gas has a plunger with a needlelike structure that engages into a hollow cavity and offers variable conductance depending upon the position of the needle in the cavity. A gate valve offers maximum possible conductance in its fully open position and offers complete isolation in the closed position. The gate valve consists of a plate with gasket and the plate can be lifted
Pipe Flow
Published in Ahlam I. Shalaby, Fluid Mechanics for Civil and Environmental Engineers, 2018
While a globe, needle, or butterfly valve may be used if the objective is to be able to carefully regulate or throttle the flow, the globe valve is one of the most common valves. Although it is relatively inexpensive, it yields a relatively large head loss. A globe valve closes a hole placed in the valve and is used to control the flowrate, Q where frequent valve operation is required and to change the direction of flow. Although the globe valve results in a larger flow resistance (higher head loss coefficient, k) than the gate valve, it also allows a closer regulation (throttling) of the flow, as it provides convenient control between the extremes of fully closed and fully open. Table 8.10 presents head loss coefficients, k for a fully open or a partially open globe valve. Furthermore, the needle valve is designed to provide a very fine control on the flowrate.
Hydraulic Power Distribution
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
Like their fixed counterparts, adjustable orifices are also among the popular methods for noncompensation flow control in many applications. Among all different designs of adjustable orifices, needle valves are probably the most commonly used. As depicted in Figure 3.30, needle valves are designed to finely control the orifice area by turning the needle to adjust the opening of the valve. Needle valves are often used as meter-in or meter-out flow control in many hydraulic systems. Because it is always associated with a large energy loss in controlling flow using either fixed or adjustable orifices, these types of flow control valves are generally used only on low-power systems or on temporal rate control applications.
Analysis of fluid flow through a bidirectional cone throttle valve using computational fluid dynamics
Published in Australian Journal of Mechanical Engineering, 2021
Yong Sang, Xudong Wang, Weiqi Sun
As can be seen from Figure 4, the overall behaviour of the needle valve is the same for different valve openings and flowing direction. Every pressure–flow curve fits well with the flow equation mentioned above. The pressure–flow curves of the bidirectional needle valve at different valve openings were obtained using Fluent software. It is helpful for engineers to realise precise flow flux control under specific conditions. Large amounts of data can be derived so that the relationship between the volumetric flow rate and the pressure difference can be studied and the relationship equation can be found utilising mathematical method such as curve fitting. Figure 4 shows that there is discrepancy on the pressure–flow characteristic as the fluid flow’s direction is changed under the same valve opening. Thus, close attention should be paid as the flow direction is reversed when the needle throttle valve is used under some specific conditions. It can also be observed that the slope of the pressure–flow curve is greater as the forward flow passes through the valve orifice under the fixed valve opening, which indicates that the flow variation is smaller with the increase of the pressure difference across the valve. Therefore, the needle valve has a better control ability as the forward flow passes through the valve orifice than that of the reverse flow while operating. The discrepancy would be analysed later with the flow information obtained during the simulation.