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Control Valves
Published in Douglas O. J. deSá, Instrumentation Fundamentals for Process Control, 2019
Before we proceed further, let us consider how control valves are modified for use in extreme operating conditions, such as either cryogenic or very hot fluid applications. When used in these applications, the body materials have to be chosen very carefully, for the process operating conditions are liable to change the normal characteristics of the materials used. For example, ordinary carbon steel, when subjected to very low temperatures, becomes brittle and therefore very prone to cracking. This makes it quite unsuitable as a material for the valve body. Similarly, there are other parts of the valve where the materials used must also be given due consideration. The most striking feature of the valves associated with these services is the extended bonnet. What is an extended bonnet? The simplest way to describe it is as an extension piece that fits between the valve body and the valve yoke, which contains seals for the sliding valve stem to enable it to fulfill the dual functions of effectively preventing the process fluid from escaping and of keeping the external conditions from affecting the process fluid. A further use for the extended bonnet is to provide the means of maintaining the degree of insulation of the process line involved, without interference to the stem itself.
Types of Corrosion in the Offshore Environment
Published in Karan Sotoodeh, Coating Application for Piping, Valves and Actuators in Offshore Oil and Gas Industry, 2023
The other example of galvanic corrosion in the offshore industry associated with butterfly valves has to do with contact between graphite and an active metal in a corrosive environment. Butterfly valves are a type of valve used to stop/start fluid such as seawater in the Norwegian offshore industry. Seawater contains chloride and is known as a corrosive service that acts as an electrolyte. The valve stem area is filled with soft materials called stem sealing or packing. Graphite packing is common for the stem sealing of industrial valves, as graphite can be used for a wide range of temperatures, in high-pressure applications and in corrosive environments. Figure 1.27 illustrates a valve stem with three graphite packing layers around the stem sealing. If the valve stem is selected in a less noble grade of stainless steel, such as 13Chromium or 22Chromium stainless steel grades, these stem materials are prone to galvanic corrosion in contact with the graphite packing and corrosive seawater media. This type of galvanic corrosion is internal, as it is caused by the fluid service, unlike the previous example. The solution that has been proposed, accepted and implemented by material and valve engineers to prevent galvanic corrosion between graphite packing and stainless-steel stems in the presence of seawater is to isolate the graphite packing with a lip seal; one lip seal is placed at the bottom of the graphite packing to prevent the seawater service fluid from coming into contact with the packing and thus prevent galvanic corrosion, as illustrated in Figure 1.28. The lip seal shown in white in Figure 1.28 is made of a soft, thermoplastic material, such as Teflon, which is energized with a metallic spring in Inconel 625 material in this case.
Overview and introduction
Published in Tom Denton, Automobile Mechanical and Electrical Systems, 2018
The most common type of oil seal is the neoprene (synthetic rubber) radial lip seal. The seal is fitted into a recess and the soft lip rubs against the rotating component. The lip is held in place by a spring. Figure 1.98 shows this type of seal; note how the lip faces the oil such that any pressure will cause the lip to fit more tightly, rather than allow oil to be forced underneath. Figure 1.98 shows a valve stem oil seal, which prevents oil entering the combustion chamber past the inlet valves.
The flow and cavitation characteristics of cage-type control valves
Published in Engineering Applications of Computational Fluid Mechanics, 2021
Zhi-xin Gao, Yang Yue, Jia-yi Wu, Jun-ye Li, Hui Wu, Zhi-jiang Jin
A typical cage-type control valve structure is shown in Figure 1. It consists of the valve body, valve seat, valve cage, valve core, valve bonnet, and valve stem. When used in high-pressure drop conditions, multi-cages are required. The commonly used multi-cages are shown in Figure 2, where the cage number can be adjusted according to relevant demand. Figure 2 shows that there are dead zones in the regulation process if the mentioned commonly used multi-cages are installed in control valves. Figure 3 shows the commonly used multi-cages to avoid dead zones during the regulation process, where the structure of the outermost cage is the same. For valve cage 1, the cage number can be adjusted according to relevant demand. For valve cage 2, the valve core of cage-type control valves is replaced by a movable valve cage. Furthermore, the valve cages shown in Figure 3 have limited decompression ability.
RUR53: an unmanned ground vehicle for navigation, recognition, and manipulation
Published in Advanced Robotics, 2021
Nicola Castaman, Elisa Tosello, Morris Antonello, Nicola Bagarello, Silvia Gandin, Marco Carraro, Matteo Munaro, Roberto Bortoletto, Stefano Ghidoni, Emanuele Menegatti, Enrico Pagello
Since the distance between the wrenches and the valve stem is known and fixed, the arm automatically moves in front of the valve stem to allow the vision system to frame it. The valve detector identifies the valve position in the images so that the robot center the cameras in front of it. Positioning the cameras in front of the valve considerably reduces the noise caused by reflections and shadows, and the Canny Edge Detector [22] can be exploited without loss of performance.
Exact shell solutions for conical springs. II. Radial cylindric curb
Published in Mechanics Based Design of Structures and Machines, 2023
In the current manuscript, the disk springs with different degrees of freedom on the inner and outer surfaces are investigated using the variation methods. Such washers are known from the patent (Muhr et al. 2009). The invention relates to a spring plate for a valve spring of an internal combustion engine. The spring plate can be connected directly to the valve stem of a charge changing valve while engaging an annular groove in the valve stem. Spring plates of this type hold and center the valve springs of charge changing valves which are arranged concentrically relative to the valve stem and which are supported more particularly by a second spring plate at the cylinder head. The valve is actuated by pressure forces being applied to the free end of the valve stem. The free end projects beyond the spring plate, by cams, rocker arms or valve levers. Between the actuating elements and the spring plate it is possible to place offsetting devices. The objective is achieved by providing a spring plate for a valve spring of an internal combustion engine. The spring plate can be connected directly to the valve stem of a charge changing valve while engaging an annular groove in the valve stem. An annular disk is arranged on the valve spring and two supporting tongues which are directed radially inwardly from the annular disk and whose inner ends, in a plan view of the Spring plate, comprise recesses for engaging an annular groove. An assembly consisting of a charge changing valve of an internal combustion engine with a valve stem has an annular groove and a spring plate for a valve spring. The spring plate is directly connected to the valve stem while engaging the annular groove. The spring plate is provided with an annular disk for being arranged on the valve spring and with two supporting tongues which are directed radially inwardly from the annular disk and whose inner ends, in a plan view of the annular disk, comprise recesses for engaging the annular groove. By providing only two supporting tongues it is possible to stiffen the spring plate without substantially increasing its mass. Furthermore, the production of the spring plate is simplified and it becomes easier to fit it to the valveshaft. Consequently, the designer needs frequently the calculation formulas for the disk springs, which are fitted upon the bolt shaft or radially restrained movement to outer direction. The latter design case appears, if the washer is placed inside the cylindrical cavity in the rigid metal block. The actual manuscript investigates these restrictions and provides the formulas for the routinely calculations of the assembled disk springs and Belleville washers.