Ball Valve - How They Work
A ball valve is a shut off valve that controls the flow of a liquid or gas by means of a rotary ball having a bore. By rotating the ball a quarter turn (90 degrees) around its axis, the medium can flow through or is blocked. They are characterized by a long service life and provide a reliable sealing over the life span, even when the valve is not in use for a long time. As a result, they are more popular as a shut off valve then for example the gate valve. For a complete comparison, read our gate valve vs ball valve article. Moreover, they are more resistant against contaminated media than most other types of valves. In special versions, ball valves are also used as a control valve. This application is less common due to the relatively limited accuracy of controlling the flow rate in comparison with other types of control valves. However, the valve also offers some advantages here. For example, it still ensures a reliable sealing, even in the case of dirty media. Figure 1 shows a sectional view of a ball valve.
Standard ball valves consist of the housing, seats, ball and lever for ball rotation. They include valves with two, three and four ports which can be female or male threaded or a combination of those. Threaded valves are most common and come in many varieties: with approvals for specific media or applications, mini ball valves, angled ball valves, ISO-top ball valves, with an integrated strainer or a bleed point and the list goes on. They have a wide range of options and a large operating range for pressure and temperature.
For more information on a threaded connection, read our ball valve connection types article.
Hydraulic ball valves are specially designed for hydraulic and heating systems due to their high operating pressure rating and hydraulic and heating oil resistance. These valves are made of either steel or stainless steel. Besides these materials, the seats also make hydraulic valves suitable for high operating pressure. The seats of these valves are made of polyoxymethylene (POM), which is suitable for high pressure and low temperature applications. The maximum operating pressure of hydraulic ball valves goes above 500 bar while the maximum temperature goes up to 80°C.
Ball valves are used for both on/off and throttling service. Ball valves are similar to plug valves but use a ball-shaped seating element (Figure 4.56). They are quick-opening and require only a quarter-turn to open or close. They require manual or power operators in large sizes and at high operating pressures to overcome the operating torque. They are equipped with soft seats that conform readily to the surface of the ball and have a metal-to-meal secondary seal. If the valve is left partially open for an extended period under a high pressure drop across the ball, the soft seat may become damaged and may lock the ball in position. Ball valves are best suited for stopping and starting flow but may be used for moderate throttling. Compared with other valves with similar ratings, ball valves are relatively small and light.
Flanged ball valves are characterized by their connection type. The ports are connected to a piping system via flanges that are usually designed in accordance with a certain standard. These valves provide a high flow rate since they typically have a full-bore design. When choosing a flanged ball valve, besides the pressure rating, you also have to check the flange compression class which indicates the highest pressure this connection type can withstand. These ball valves are designed with two, three or four ports, they can be approved for specific media, have an ISO-top and everything else a standard quarter turn valve could have. They are typically made out of stainless steel, steel, or cast iron.
Vented ball valves look almost the same as the standard 2-way ball valves when it comes to their design. The main difference is that the outlet port vents to the environment in closed position. This is achieved by a small hole that is drilled in the ball and in the valve body. When the valve closes, the holes line up with the outlet port and release the pressure. This is especially useful in compressed air systems where depressurization provides a safer working environment. Intuitively these valves look like 2-way ball valves while in fact they are 3/2-way due to the small borehole for venting.
Ball valves are not recommended for FO applications. Generally, it is possible to reduce the opening time of the fail open actuated valve by installing a quick exhaust valve on the control panel to release the instrument air from the pneumatic actuator in the fail mode quickly. However, a ball valve’s seat and disk are in contact during the opening and closing, which can jeopardize FO. In addition, moving the relatively large and heavy ball requires a higher stem torque, a larger actuator, and perhaps a longer opening time. The ball valve manufacturer was asked about the possibility of using a soft seat ball valve for this application. The manufacturer believed that FO of the soft seat ball valve in 2 s could cause damage to the soft seat because of the very quick contact with the ball. On the other hand, the manufacturer stated that a 2-s opening time can be achieved with a metal seat ball valve. But a metal seat has the disadvantage of possible leakage, unlike a soft seat, and it is a more costly solution than butterfly and axial control valves due to the valve and the large mounted actuator.
Unlike FO applications, a ball valve is a good choice as a blowdown valve with less opening time than an FO valve. Fig. 12.25 shows a blowdown ball valve to release the overpressured fluid from the equipment in an emergency mode. The blowdown ball valve is an 18″ Class 2500 in a 6MO body and a metallic Inconel 625 seat, which may need 18 s for opening. Blowdown or FO valves on flare lines usually see low operating temperatures because of the released gas pressure drop. Gas pressure drop reduces the operating temperature to ? 46°C or even lower, so the minimum design temperature is typically below ? 100°C. The low temperature application makes it impractical to use 22Cr duplex with a minimum design temperature of ? 46°C for the valve, so 6MO or Inconel 625 are the correct choices of materials. An extended bonnet is used for the valve to keep the packing away from the relatively cold service, similar to cryogenic valves.
Ball valve working principle
To understand the working principle of a ball valve, it is important to know the 5 main ball valve parts and 2 different operation types. The 5 main components can be seen in the ball valve diagram in Figure 2. The valve stem (1) is connected to the ball (4) and is either manually operated or automatically operated (electrically or pneumatically). The ball is supported and sealed by the ball valve seat (5) and their are o-rings (2) around the valve stem. All are inside the valve housing (3). The ball has a bore through it, as seen in the sectional view in Figure 1. When the valve stem is turned a quarter-turn the bore is either open to the flow allowing media to flow through or closed to prevent media flow. The valve's circuit function, housing assembly, ball design, and operation types all impact the ball valve's operation are are discussed below.Circuit function
The valve may have two, three or even four ports (2-way, 3-way or 4-way). The vast majority of ball valves are 2-way and manually operated with a lever. The lever is in line with pipe when the valve is opened. In closed position, the handle is perpendicular to the pipe. The ball valve flow direction is simply from the input to the output for a 2-way valve. Manually operated ball valves can be quickly closed and therefore there is a risk of water hammer with fast-flowing media. Some ball valves are fitted with a transmission. The 3-way valves have an L-shaped or T-shaped bore, which affect the circuit function (flow direction). This can be seen in Figure 3. As a result, various circuit functions can be achieved such as distributing or mixing flows.
Inspecting Pipes in Exterior Walls and Pipe Insulation
Locating water pipes in exterior walls should be avoided. If pipes are located in exterior walls, in addition to insulating the pipe, the homeowner should ensure that as much cavity insulation as possible is installed between the pipe and the outer surface of the wall. In cold climates, having pipes in unconditioned attics should be avoided. The image above is of uninsulated water supply pipes in an unconditioned basement.
Insulating water pipes can save energy by minimizing heat loss through the piping. Insulating pipes will reduce the risk of condensation forming on the pipes, which can lead to mold and moisture damage. Insulation pipe can protect the pipes from freezing and cracking in the winter, which can cause considerable damage in the walls of the home and result in significant home repair bills for the homeowner. Studies by the Department of Energy (DOE’s) Building America program have shown that distribution heat loss in uninsulated hot water pipes can range from 16% to 23%, depending on the climate. Adding 3/4-inch pipe insulation can cut overall water heating energy use by 4% to 5% annually.
The best practice is to avoid having water pipes located in exterior walls or through unheated attics. It is preferable to have plumbing fixtures aligned with interior walls. If pipes are located in exterior walls, the pipes should be insulated. To further protect the pipes from heat loss, the wall cavity containing the pipes should be air-sealed by caulking or foaming all seams between the back wall of the cavity and the framing, and by sealing any holes through the framing for the piping. In addition, cavity insulation should be installed behind the pipes, between the pipes and the exterior wall.
If the house has a hydronic (steam or hot water) heating system, heat loss can be reduced by as much as 90% by insulating the steam distribution and return pipes, which provides a quick payback on investment.
Insulated copper coil is one of the main aspects of many of Joseph Henry’s experiments in the field of Electricity and Magnetism is the large coils or helices of copper wire or ribbon he used. These coils were often quite large, usually containing over 1000ft of wire and sometimes weighing over 10lbs. As described by Henry in his papers, these coils were often insulated by wrapping the wires in cotton, dipping them in beeswax, and then painting.
Optimization and intelligent manufacturing are of particular interest and important to improve the severe situation of excessive mass and uneven stress distribution for three branch joint in treelike structures. In this work, the optimal shape of the three-branch joints under vertical load is studied by topology optimization method, and the complex topology optimization Y joint is manufactured using threedimensional (3D) printing technology because it is difficult to produce by conventional manufacturing processes. First, the original model is optimized by using the OptiStruct solver in HyperWorks version 14.0 (64-bit) software, and the element density cloud map and element isosurface map of the model are obtained. Then, the static behaviors of the topology optimization model are compared with those of the hollow spherical joint model which is commonly used in engineering and those of the bionic joint model based on empirical design. Finally, the 3D printing technology is used to produce the topology optimization joint model, the hollow spherical joint model, and the bionic joint model.
- Creado: 29-08-21
- Última sesión: 29-08-21