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Posted on Aug 1, 2021
A ball valve controls the flow of a liquid or gas utilizing a rotary sphere. It functions as a shut-off valve by rotating the ball at about 90 degrees around its axis, allowing the liquid to enter and exit. Compared with other valves, ball valves have a longer service life and are capable of providing strong sealing over their lifespan. Its long-term reliability is the key reason why they are so popular in all kinds of industries, even more so than gate valves. Besides, ball valves are less susceptible to contaminated liquid compared with other types of valves. They can also be used as a control valve in some scenarios, but such instances are rare because ball valves are less accurate in terms of flow control.
Besides, ball valves are less susceptible to contaminated liquid compared with other types of valves. They can also be used as a control valve in some scenarios, but such instances are rare because ball valves are less accurate in terms of flow control.
To understand how a ball valve works we need to first understand its most important components. The core component is the ball that rotates around its axis by 90-degree turns. It is a sphere with a hole or tunnel through its center and a connection to a shaft (also called the valve stem) that rotates it. Based on the position of the ball the liquid can flow through or gets blocked. But for this type of valve to work as intended more parts are needed. You can see them in the image below. The seats (o-rings) are donut-shaped discs that serve as a seal between the body housing and the ball.
Two other important components are the bonnet and the packing. The bonnet is the part of the housing that encapsulates the stem and the packings, additional seals with more flexibility around the stem to prevent the liquid from flowing out. Finally, externally a lever or a gear is needed (can be a manual, pneumatic, hydraulic actuator) to control the ball position. Every time the valve stem makes a 90 degree turn the tunnel changes its status from open to close and vice versa.
There are a number of benefits in using a ball valve. They are very easy to operate, and they have a long service life. They require no extra lubrication and have low production and maintenance costs. Ball valves can withstand high pressure, high velocity, and high temperature flows while being very rugged and usually don’t require much maintenance. . That is why they are suitable for a wide range of industrial applications and offer many years of reliable water flow controls. Let’s take a closer look at the most important benefits:
A standard ball valve is the most basic type of ball valve. It is made up of a housing, seats, a rotary ball, and a lever. The standard ball valve may have two to four ports for the fluid to flow. The most common is the two-way setup which includes one inlet and one outlet port.
A hydraulic ball valve is a type of ball valve which is specifically designed with a hydraulic and a heating system. The hydraulic ball valve has a high operating pressure rating and high resistance to hydraulic and heating oil. It is typically made of steel or stainless steel, which is very resistant to corrosion. What enables ball valves to operate at high pressure is the valve seat, which is typically made of polyoxymethylene. It is the perfect material that allows the valve to be used in low-temperature applications.
The flanged ball valve is the type of ball valve which is distinctive due to its connection type. The ports of the flanged ball valve are connected to a piping system via a device called the flanges. The flanges are the type of device which are usually designed to fit with a certain standard. The flanged type is capable of providing a high flow rate because of a full-bore design. It is very important to keep in mind that when choosing this kind of valve, people also need to check the flange compression class. The flange compression class indicates the highest pressure this connection type can withstand.
This type of valve utilizes an electric motor to regulate the fluids automatically and can be opened or closed by doing a quarter turn. The motorized valves feature tight seals even after numerous cycles and a long lifespan. They are reliable especially in applications where oversight is limited. Another key function of motorized ball valves involves detecting and responding to various flow conditions. This is usually achieved by incorporating a digital position sensor into the motorized device. And in terms of materials, the valves are typically made of stainless steel for the maximum corrosion resistance. Other popular body materials include brass, bronze, PVC, and so on.
A ball valve can have up to four tunnels (or ports). Therefore we can distinguish between 2-way, 3-way and 4-way valves, with the former being the most common one. (2-way, 3-way or 4-way). 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. 3-way valves have an L-shaped or T-shaped bore, which affects the circuit function. Below you can see an illustration of the different functions for distributing or mixing flows.
Most valves are manually controlled by a lever. That handle is connected on top of the ball valve and directly controls the opening and closing of the valve. If installed correctly, the handle should be parallel to the pipe when it’s open, and perpendicular to the pipe when closed. As an operator, you should always take note of the direction of the handle as it is a direct indication of whether a valve is open or closed. For bigger ball valves, you might need to install a handle extension to avoid breaking the handle. As with other parts of the ball valve, the handle is just as important that needs to be maintained or even replaced when necessary.
In this design, the ball is pressed or welded by two parts. It is the cheapest of the three but also the least reliable because you cannot open it for cleaning or maintenance. This is also why this type of housing has the lowest demands in the industry.
Ball valves with two-piece housings are much easier to clean and maintain because the parts are attached through a threaded connection. However, the valve must be removed from the pipe completely to detach the parts.
This design is the most expensive but benefits from easy disengagement for maintenance. The parts of a 3pc ball valve are usually connected using bolts. You do not have to remove the valve entirely from the pipe to service it.
The most common housing materials are brass, stainless steel, carbon steel, and PVC . The ball is usually made of chrome-plated steel or brass, stainless steel or PVC. The seats (we explained them above) are often made of Teflon, but sometimes other metals or synthetic materials. Let us take a look at each material and its advantages and drawbacks:
The most popular metal used for valve housings is brass. Brass is a copper-zinc alloy with excellent mechanical characteristics. Brass valves are used to control the flow of water, gas, oil, air, and many more fluids. Dezincification can be caused by chloride solutions (such as seawater) or demineralized water. Dezincification is a type of corrosion in which the zinc in an alloy is eliminated. This results in a porous structure with low mechanical strength. For an air ball valve, a brass housing is perfect. Manual 2-way brass ball valves and 3-way brass ball valves are available.
+ Long product life, wide range of applications
− Dezincification can be an issue
Stainless steel is the preferable choice when operating in harsh conditions, and with corrosive liquids. Application examples are seawater, swimming pools, osmosis systems, high temperatures and certain chemicals. The most common stainless steel ball valves use 304 and 316, with 316 having the best corrosion resistance. Stainless steel ball valves typically require more operating torque than brass or PVC valves. This is especially important when used in combination with an electric or pneumatic actuator.
+Long product life, wide range of applications
− Higher cost, more torque needed to rotate the ball
Carbon steel ball valves have a matte appearance that resembles cast iron. This metal has a lower melting point and less chemical resistance than stainless steel, but it is more malleable, stable, and has better heat distribution due to its high carbon content. Carbon ball valves can be utilized in completely open or completely closed positions. Depending on the implementation circumstances, throttling carbon steel ball valves may result in early seal breakage and/or inability to press the valve grip.
+ High corrosion-resilience, good tensile strength, durable, relatively cheap
− Prone to rust and staining
PVC valves, except for ISO-top valves, are commonly used in irrigation, water supply, and drainage, as well as corrosive media. Polyvinyl chloride (PVC) is a type of plastic. Most salt solutions, acids, bases, and organic solvents are resistant to PVC. PVC is not suited for temperatures beyond 60 degrees Celsius, nor is it resistant to aromatic or chlorinated hydrocarbons. Because PVC is not as sturdy as brass or stainless steel, PVC ball valves can only withstand a lesser pressure. Chlorinated PVC is very similar but can withstand higher temperatures, making it suitable for hot water applications.
+ Good corrosion-resistance, low cost
− Limited in terms of pressure and temperature, shorter lifespan
As we mentioned before, the ball valves ball is the most crucial component. The vast majority of ball valves have a floating ball design. The sphere is held in place between two sealing rings and suspended in the liquid. It is also supported by a valve seat. High-end valves typically have a trunnion design where the ball is held from the top and bottom to reduce the load on the valve seats. The operating torque is usually lower for this type of valve.
Ball valves with reduced bore are the most common. Although they suffer from friction losses, they are relatively smaller compared to other types of valves. A full bore valve has an identical diameter with the pipe. It has no extra friction losses and is relatively easier to maintain. And finally, the V-shaped ball valve has a hole in the ball with 'V' shaped profile. Its key advantage is the precise control of the rotary ball. You can adjust the profile so that the flow becomes linear as well.
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