A choke valve is a type of flow control valve that is used to regulate the flow of fluids, such as gases or liquids, in a pipeline. Choke valves are typically used in the oil and gas industry to control the flow of well fluids, such as oil or natural gas, from a wellhead to a production facility. The valve is designed to reduce the flow rate by creating a restriction in the pipeline, which can be adjusted to achieve the desired flow rate. This is typically achieved by using a tapered orifice or a variable orifice, which can be adjusted to increase or decrease the restriction in the pipeline. If you look at a kitchen tap, a choke valve executes a very similar function. In essence, a choke valve can be considered a more robust and highly engineered kitchen tap.
How does a choke valve work?
A choke valve works by regulating the flow of fluid through a restriction in the valve, which can be adjusted to achieve the desired flow rate. The restriction is typically created by an orifice, which is a small opening through which the fluid must pass. In a fixed choke valve, the orifice is a fixed size and cannot be adjusted, while with an adjustable choke valve, the orifice can be adjusted to vary the restriction in the pipeline.
The flow rate through the valve is controlled by adjusting the position of the orifice or the restriction. When the orifice or restriction is fully open, the flow rate is at its maximum, while when it is fully closed, the flow rate is zero. To control the flow rate, the orifice or restriction is adjusted to a partial open position, which creates a pressure drop across the valve and reduces the flow rate. This can be done manually or automatically, through the use of actuators and control systems.
Choke valves are commonly used in oil and gas industry for controlling the flow rate of well fluids, such as oil or natural gas, from a wellhead to a production facility. In addition, choke valves are also used in many other process industries, such as power generation, chemical, and water treatment.
Why would you need a choke valve?
Think about it like this; you have high pressure coming out of your faucet and you need to reduce that pressure so you don’t waste any water or put undue strain on the infrastructure helping to transmit it. Or maybe you just want to hit that perfect sweet spot of pressure for washing your hands.
To achieve this, we must create a pressure drop or restriction. This will speed up the fluid, which if it’s oil or gas being extracted from the ground, normally has particles in it. So we need to control this process, in order to mitigate the risk of these particles — most commonly sand in energy producing applications — from causing damage to the piping infrastructure. Or maybe there’s a specific amount of production that we need to achieve for a given process. Each of these requirements, when we open the valve to meet them, will, in most cases, bleed down the upstream pressure and may require further adjustments to meet a specific application goal. This is where the control a choke valve provides is extremely beneficial and it is the control it enables that serves as the main purpose behind having such a valve in the first place.
Material choice, design, and choke valve quality are critical considerations when choosing a choke as erosion, velocity induced erosion, and cavitation are just a few of the conditions and threats a choke valve will face with it being so close to the wellhead. Given all the extreme conditions and pressures a choke valve encounters, selecting the right choke is critical since it is one of the most critical valves in your system.
Sizing, material selection, and design need to be some of the main things you think about when selecting a choke valve. To help with this process, Master Flo has developed a sizing program called SizeFlo to make navigating these options easier.
Are there different types of choke valves?
Yes, there are different types of choke valves designed to handle different types of fluids and different flow conditions. Some common types include:
Conventional Choke Valves: These are the most common types of choke valves and have a fixed or adjustable orifice that creates a restriction in the pipeline. They are typically used in low-pressure, low-flow applications.
Positive Choke Valves: These valves use a piston or plug to create a restriction in the pipeline. They are typically used in high-pressure, high-flow applications.
Multi-Stage Choke Valves: These valves have multiple orifices or restriction stages, which can be adjusted independently. They are typically used in applications where precise flow control is required.
Automatic Choke Valves: These valves have built-in actuators and control systems that automatically adjust the flow rate based on input from sensors or control systems. They are typically used in applications where the flow rate needs to be continuously adjusted.
Hydraulic choke valves: These valves use a fluid-powered actuator to control the flow rate. They are commonly used in remote or hazardous locations where manual adjustments are not feasible.
In addition to above types of choke valves, there are some other variations as well like ‘self-operated choke valves’ which can be actuated by pressure changes of the fluid itself, and ‘smart choke valves’ that uses advanced technology for controlling the flow rate.
What components are in a choke valve?
A choke valve typically consists of several key components, including:
Body: The body is the main housing of the valve that holds all of the other components in place. It is typically made of metal, such as steel or stainless steel, and is designed to withstand the pressure and temperature of the fluid being controlled.
Orifice: The orifice is the restriction in the pipeline that controls the flow rate. It can be a fixed size or adjustable, depending on the type of valve. The orifice is typically located within the body of the valve.
Plug or needle: The plug or needle is the component that regulates the flow rate by moving into or out of the orifice. It can be cone-shaped or cylindrical, depending on the type of valve.
External sleeve and cage: The external sleeve is the component that regulates the flow rate by moving over top of the cage.
Actuator: The actuator is used to control the position of the plug or needle, and can be manual or powered. The actuator can be a lever, knob, electric motor, or hydraulic cylinder.
Seals: Seals are used to prevent fluid leakage around the plug or needle, and are typically made of materials such as Teflon, VITON, NBR, depending on the type of fluid and temperature.
Control system: The control system is used to automatically adjust the position of the plug or needle, and can include sensors, switches, and controllers.
Some choke valves may include additional components such as a stem, which connects the actuator to the plug or needle, and a bonnet, which covers the valve body and holds the stem in place.
Choke valves can also have additional features like pressure relief, bypass, or anti-surge control. These features can be added to the valve to provide additional safety and control capabilities.
Do choke valves come in different sizes?
Yes, choke valves come in different sizes to meet the flow control requirements of various applications. The size of the valve is determined by the size of the pipeline in which it will be installed and the flow rate that needs to be controlled.
The size of a choke valve is usually specified by the pipe size and pressure rating of the valve. The pipe size refers to the diameter of the pipeline, and can range from small diameter valves for low-pressure applications to large diameter valves for high-pressure applications. The pressure rating refers to the maximum pressure that the valve can handle and is usually specified in pounds per square inch (psi) or bar.
The size of the orifice in a choke valve is also important, as it determines the restriction in the pipeline and the flow rate that can be achieved. The size of the orifice can be fixed or adjustable, depending on the type of valve. Adjustable choke valves typically have a range of orifice sizes that can be used to achieve a wide range of flow rates.
It’s important to select the right size of choke valve for the application to ensure that it can handle the fluid flow rate and pressure, and that it will fit properly in the pipeline. It’s also important to select the right size of orifice to achieve the desired flow rate and to minimize the pressure drop across the valve.
Are there different pressure ratings for choke valves?
Yes, choke valves have different pressure ratings, which refer to the maximum pressure that the valve can handle. The pressure rating is usually specified in pounds per square inch (psi) or bar. The pressure rating of a valve is determined by the material and construction of the valve, and is usually based on the maximum allowable working pressure (MAWP) for the valve.
Choke valves are available in a wide range of pressure ratings to meet the requirements of different applications. For example, low-pressure valves are typically rated for pressures up to 150 psi, while high-pressure valves can be rated for pressures up to 20,000 psi or more.
It is important to select a choke valve with the appropriate pressure rating for the application to ensure that it can safely handle the pressure of the fluid being controlled. If the valve is not rated for the maximum pressure of the fluid, it could fail and cause damage or injury.
When selecting a choke valve, it is important to consider the pressure rating, as well as the size, material, and construction of the valve, to ensure that it can handle the fluid flow rate and pressure, and that it will fit properly in the pipeline. It’s also important to consider the temperature rating of the valve to make sure that it can handle the temperature of the fluid.
Is there a certification process or governing body for choke valves?
Yes, there are several organizations that certify and govern choke valves to ensure that they meet certain safety and performance standards. The most common certifying bodies for choke valves are:
American Petroleum Institute (API): The API is a trade organization for the oil and gas industry, and it publishes standards for the design, manufacture, and testing of choke valves. API-6A is the standard for wellhead equipment, and it covers the requirements for choke valves used in oil and gas production.
American Society of Mechanical Engineers (ASME): ASME is a professional organization for mechanical engineers, and it publishes standards for the design, manufacture, and testing of valves, including choke valves. The ASME B16.34 standard covers the requirements for valves, including choke valves, used in industrial and commercial applications.
National Association of Corrosion Engineers (NACE): NACE is a professional organization for corrosion engineers and it publishes standards for materials and coatings used in the oil and gas industry, including choke valves.
These certifying bodies have specific requirements for the design, materials, testing, and documentation of choke valves, and manufacturers must meet these requirements in order to have their valves certified. This certification process includes testing of choke valves to ensure that they meet the standards set by these organizations, and that they are safe for use in the intended applications.
In addition to the certifying bodies mentioned above, there are also other international standards like ISO, EN, and JIS that can be used in specific regions or countries. It’s important to check the local regulations and standards to ensure that the valves meet the requirements for the specific application and location.
What is the most important benefit a choke valve provides?
The most important benefit of a choke valve is its ability to precisely control the flow rate of fluids, such as gases or liquids, in a pipeline. Choke valves are used to reduce the flow rate by creating a restriction in the pipeline, which can be adjusted to achieve the desired flow rate. This is accomplished by using a tapered orifice or a variable orifice, which can be adjusted to increase or decrease the restriction in the pipeline.
Being able to control the flow rate is important in many industries, such as oil and gas production, where it is crucial to maintain a consistent flow rate to optimize production and prevent damage to the wellhead or production facility. In addition, choke valves are also used in many other process industries, such as power generation, chemical, and water treatment, where it is important to control the flow rate to ensure safe and efficient operation of the process.
Other benefits of choke valves include:
Safety: By controlling the flow rate, choke valves help to prevent over-pressurization and potential accidents.
Efficiency: By maintaining a consistent flow rate, choke valves help to optimize production and reduce energy consumption.
Durability: Choke valves are typically made of durable materials, such as steel or stainless steel, and are designed to withstand the pressure and temperature of the fluid being controlled.
Versatility: Choke valves come in different types and sizes to meet the flow control requirements of various applications.
A critical part of your flow control equation
To summarize, the most important benefit of a choke valve is its ability to precisely control the flow rate, which is essential for safe and efficient operation in many industries.
Given the critical role it plays, selecting a choke that provides superior control and longevity is paramount to success. It is for this reason why so many of the world’s leading energy producers have relied on Master Flo — and our innovative technological flow solutions — for the past 45 years to facilitate their flow control success.
