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Choosing a control valve is challenging even for vetted technicians. To choose the right one, you should possess a basic knowledge of regulation technologies. You also need an understanding of different types of control valves and their applications.
Now, what is a control valve, and what types of valves exist? At Blackhawk Supply, we'll be happy to share what we know!
Keep reading to learn about the technology behind control valves, their categories and types, and their various industrial applications.
The control valve is a power-operated device designed for controlling the flow and pressure of fluids and steam. The degree of regulation (from full capacity to minimal) is based on the signal from a controller.
Control valves are an essential component of industrial control systems. These devices are used to control processes, such as liquid level, pressure, velocity, and temperature, but within the correct operating range. Additionally, they ensure efficient operations and the long-lasting service life of your equipment.
These valves are used in many residential and industrial applications. For example, you can find them in HVAC (heating, ventilation, and air conditioning) systems, unit ventilators, fan coil units, VAV boxes, and various other devices.
All control valves share the same goal (flow, pressure, and temperature control), but they are designed for slightly different applications. The most widespread types of control valves are:
Rotary control (ball and butterfly valves)
Linear control (globe and diaphragm valves)
Three-way control
Self-acting control
Let's look at these control valves and their features in greater detail.
Fluids in the rotary valves (also known as quarter-turn valves) travel through rotated passages in a transverse plug. As the name suggests, they use a rotating closure element to control the flow.
This type of valve is very flexible and is compatible with many adaptive technologies. Most rotary valves are quite compact. At the same time, they work with demanding applications. Their design makes them great for dirty (particle-heavy) fluids, such as those used in refineries.
Ball valves are extremely useful for isolation applications, as they provide straight-through flow. On top of that, they are quick-acting, easily actuated, and offer a low-pressure drop. Ball valves can be operated pneumatically, electrically, and manually (based on their model, of course).
These valves have a rugged three-piece valve body in the form of a quarter-turn valve with a round hole in the center. A ball valve uses a hollow pivoting ball to control how much fluid can flow through it.
Ball valves are pretty heavy and more expensive than other control valves. However, they work great for high-capacity and high-pressure applications. You can find them in:
Building control systems
Water industries
Chemical industries
In addition to hot and chilled water, the ball valve offers excellent control of glycol mixes and steam. Plus, this type of control valve limits cavities and crevices, preventing contamination from outside sources.
Butterfly valves use quarter-turn rotation for control in high-flow applications. The butterfly valves provide a fast and easy way to start and stop the flow. Additionally, it allows for complete closure and opening of the valve, minimizing potential leakage.
These valves are operated pneumatically, manually, or electrically (akin to ball valves). Unlike a ball valve, a butterfly valve is a much more lightweight and economical solution.
Butterfly valves come in different construction materials, liner options, and other specifications. This makes them highly compatible with a wide range of industrial, water, and chemical applications.
Most companies use butterfly valves for their low-pressure drop, high-pressure recovery, and excellent flow isolation. Their typical applications include:
HVAC systems
Exhaust gases control
High-temperature services
Steam services
The plug control valve is a type of valve used to regulate the flow of a fluid in a pipe. It is a type of gate valve, and it consists of a cylindrical plug that slides in and out of the pipe to control the flow. The plug is connected to a stem, which is turned to open and close the valve. The stem is connected to a handle, which is used to operate the plug valve.
The plug valve is used in a variety of applications, including controlling the flow of water in a pipe, regulating the pressure in a pipe, and controlling the flow of oil in a pipeline. It is widely used in the oil and gas and in the food and beverage industries to control the flow of liquids in a pipe.
Linear valves (multi-turn valves) use a sliding-stem mechanism to push the closure into the open and close positions for flow control. This control valve has a slower operation speed but great positional stability and accuracy (1:1 flow control).
Linear valves have a straightforward and durable design. These valves are also very versatile due to a large variety of available trim sizes and options. Some of the most prevalent subtypes of linear valves are globe valves and diaphragm valves.
Globe control valves regulate flow in pipelines and other applications requiring increased flow resistance or significant pressure drops.
These valves have a generally spherical valve body. The mechanism consists of two halves, a moveable plug (disc element) that separates these halves, and a stationary ring seat. In addition, the globe control valve has a stem that regulates the flow by moving up and down in the valve.
The efficiency and reliability of globe valves make them an excellent choice for a wide selection of applications, including:
Chemical feed systems
Boiler and main steam vents
Cooling water systems
Fuel oil systems
Globe valves are pretty expensive devices. However, they provide extended service life, high performance, and optimized flow passages that reduce pressure drops and destructive turbulence.
Diaphragm valves (membrane valves) are typically made of plastic, wood, or metal body with multiple ports and an elastomeric digraph. The seat in the body opens and closes the valve, controlling the flow.
These valves eliminate any chance of contamination due to their tight seal. This helps to ensure the liquids in your systems remain as sterile and clean as possible.
You can use diaphragm valves in many systems, thanks to a wide range of designs and construction material options. In addition to clean water control, you can use these valves to regulate corrosive and abrasive media. You can also use them with pneumatic control heads or process controllers to enhance the accuracy of control.
Three-way control valves are designed to open fluid flow in a pipe while closing the flow in another pipe. These valves typically have a pneumatic, multi-spring, or electric actuator for power.
A three-way flow control valve is available in two configurations: a diverter valve and a mixing valve.
These valves can control water, oil, steam, and various fluids in HVAC systems. The typical applications of the three-way valve include:
Air handling units
Boilers
Fan coils
Water chillers
A mixing valve is designed to control the supply of water in heating and cooling systems. Basically, these devices provide an easy way to mix hot and chilled waters for a comfortable temperature.
A diverter valve is named after a mechanism that opens and closes the valve in combi boilers to regulate water. The typical places where you can find diverter valves include:
Home radiators
Showerheads
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Taps
Diverter valves aren't used for standard HVAC systems and conventional boilers. Instead, they are installed in systems that supply heated water on demand.
Some types of valves, like Tee-Piece valves, combine both mixing and diverting functions. They can accept an ON/OFF or modulating signal. These valves can be used in combi boilers, showers, radiators, and regular HVAC systems.
A self-acting valve regulates the water flow with the help of temperature-sensitive fluid. This fluid expands on heating and contracts when cooled. The force created by these reactions transfers to the actuator, which opens and closes the valve.
These valves are used to regulate water and steam in heating and cooling systems. A self-acting control valve's typical applications include:
Air compressors
Air chillers
Boilers
Industrial engines
Some of the advantages of self-acting valves include easy installation and enhanced durability. Plus, these valves are self-sufficient, meaning they don't need an external power supply to operate.
The primary function of all control valves is to regulate the flow, pressure, and temperature of fluids (and other substances). Additionally, control valves can regulate air, steam, glycol mixes, and chemicals based on predefined settings.
Control valves are found in any refining, chemical manufacturing, and other industrial applications. These valves are used for process quantities and consequential control. Now, how do these valves work?
Control valves regulate the flow in loops.
At the start of the loop, a transmitter and a controller compare the current flow level with the desired level.
The controller sends a correction signal to the control device (valve).
The control valve closes to reduce the fluid flow (or opens to increase it).
The valve opens or closes to ensure the desired level of flow.
You can find many control valve types and applications used in various industries. They include food & beverage, oil & gas, pipeline, biopharma, and many others.
As you understand by now, control valves are quite complicated mechanisms. It's not just about choosing the correct type of valve. To ensure you're getting the right valve for your system, you should also consider:
Media type. Your control valve should support the liquid or gas type. For example, metal works for pressure gasses, and corrosive materials require something like PFA or PTFE.
Actuation. Do you want a hand-operated valve or an actuator that turns it off automatically? On top of that, you should consider the positioning of the valve after it loses power. For instance, a double-acting actuator maintains the last position. In contrast, the spring return actuator either opens or closes the valve after losing the signal.
Installation. Consider your management system before choosing a valve. Some types of valves support remote monitoring and control, which can make maintenance much easier. Additionally, find out how easy it is to disconnect and reconnect the valve.
Maintenance. Some valves are virtually maintenance-free, and others require regular cleaning. Needless to say, some control valve types, like ball valves, are way easier to keep clean due to their design.
Now, the list isn't exhaustive. We recommend comparing control valves based on their advantages and disadvantages, functionality, efficiency, and price.
After reading this, you should have a good idea about control valve types and applications. We hope that our guide helps you get the best device for your tasks!
Feel free to check Blackhawk Supply for a great selection of high-grade control valves from reputable manufacturers like Belimo, Johnson Controls, Honeywell, and many others. Our shop has control systems, plumbing supplies, and a ton of other miscellaneous stuff!
The introduction of the main accessories of the control valve:
Regulating valve positioner is the main accessory of the pneumatic actuator. It is used together with a pneumatic actuator to improve the positional accuracy of the valve, to overcome the friction of the valve stem and the influence of the unbalance force of the medium, and to ensure that the valve is correctly positioned by the signals from the regulator.
In the following cases, the positioner should be equipped:
1. When the medium pressure is high, and the differential pressure is large;
2. When the caliber of the regulating valve is large (DN>100);
3. High or low-temperature control valves;
4. When there is a need to increase the operating speed of the regulating valve;
5. When operating an actuator with a non-standard spring using a standard signal (spring range other than 20 to 100 KPa);
6. When used for split-range control
7. When the valve is to be operated in the reverse direction (air-closed type and air-open type can be converted to each other);
8. When it is necessary to change the flow characteristics of the valve (the positioner cam can be changed);
9. When there is no spring or piston actuator, and proportional action is to be realized
10. When electrical signals are used to operate pneumatic actuators, electrical-pneumatic valve positioners must be distributed.
Solenoid valves:
When the system needs to achieve program control or two-position control, it is necessary to use solenoid valves. Selection of solenoid valves, in addition, to considering AC and DC power supply and voltage, and frequency, must pay attention to solenoid valves and regulating the role of the valve type of relationship, can be equipped with "normally open" or "normally closed."
Suppose you need to increase the capacity of the solenoid valve to shorten the action time. In that case, you can use two solenoid valves or solenoid valves as a pilot valve and large-capacity combination of pneumatic relays.
Pneumatic Relay:
A pneumatic relay is a kind of power amplifier, it can send the pneumatic signal to a distant place, eliminate the lag caused by the lengthening of the signal pipeline, mainly used between the field transmitter and the central control room of the regulating instrument, or between the regulator and the field regulating valve, and there is also a role is to amplify or reduce the signal.
Converters:
The converter is divided into gas-electricity converter and electricity-gas converter, whose function is to realize a specific relationship between gas and electric signals to convert each other. It is mainly used to convert 0&#;10mA or 4&#;20mA electric signals or convert 0&#;100KPa gas signals into 0&#;10mA or 4&#;20mA electric signals when manipulating pneumatic actuators with electric signals.
Air Filtration Pressure Reducing Valve:
An air filtration pressure-reducing valve is an accessory in industrial automation instruments. Its primary function is to filter and purify compressed air from the air compressor and stabilize the pressure at the required value. It can be used as the air supply source and pressure stabilizing device for all kinds of pneumatic instruments, solenoid valves, cylinders, spraying equipment and small pneumatic tools.
Self-locking valve (position preserving valve):
A self-locking valve is a device to keep the valve in position. Pneumatic control valve when the gas source failure occurs, the machine can cut off the gas source signal so that the membrane chamber or cylinder pressure signal to maintain a moment before the failure of the state, so that the valve position is also maintained in the position before the failure, to play the role of position preservation.
Valve position transmitter:
When the control valve is away from the control room, in order not to the scene to accurately understand the valve switching position, we must be equipped with a valve position transmitter, that is, the valve opening the amount of institutional displacement, according to a specific law converted into electrical signals sent to the control room, this signal can be reflected in the valve of any opening of the continuous movement can also be considered as the inverse action of the valve positioner.
Travel switch (return signal):
The travel switch reflects the two extreme positions of the valve switch, and at the same time, sends the indication signal device. Based on this signal, the control room can rebel against the valve switch status to take appropriate measures.
Control Valve Arrangement:
The image below shows how a control valve can be used to control rate of flow in a line. The "controller" receives the pressure signals, compares them with pressure drop for the desired flow and if the actual flow is different, adjusts the control valve to increase or decrease the flow.
Comparable arrangements can be devised to control any of numerous process variables. Temperature, pressure, level and flow rate are the most common controlled variables.
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