Selecting a Valve for Flow Control
- Consider your fluid type (liquid or gas) and its characteristics to determine compatible valve materials. PTFE and PFA withstand many harsh or corrosive chemicals. ...
- Determine the temperature, pressure, and flow rate under which your valve will be operating. ...
- For solenoid valves, consider response time and length of time valve will be energized. ...
- Consider your maintenance requirements. ...
How do I choose a control valve?
When choosing a control valve for a process, there are many things that must be considered, including the valve's flow characteristic, its size, noise, the potential for cavitation or flashing damage, body and trim materials, actuator size and type, and its dynamic response to changes in the control signal.
How do you size a flow control valve?
When sizing a control valve, the rule of thumb is to size it so that it operates somewhere between 20-80% open at maximum required flow rate and whenever possible, not much less than 20% open at the minimum required flow rate.
What are the factors to consider when selecting a control valve?
5 Factors to Consider When Choosing a ValveMedia Type. The characteristics of the liquid or gas type being controlled will determine the valve material that should be used. ... Application Conditions. ... Valve Function. ... Actuation Method. ... Maintenance Requirements.
What type of valve is best for flow control?
For flow control applications where a ball valve is possible, such as filling a tank to a reasonable degree of accuracy, a trunnion or v-port ball valve design is usually the best choice.
How is valve size measured?
By simply measuring from the tip of the valvestem to the face of the valve with a set of calipers, you can get the valve's overall length.
How do you choose a valve class?
Valve selection is dependent on the characteristics of the services as follows.Fluid type.Fluid characteristics.Pressure and temperature limitations.Operation and maintenance requirements.
What three 3 factors are valves classified to?
Process operators classify valves by (1) flow-control elements, (2) function, and (3) operating conditions such as pressure, flow, or temperature. The most common way to classify valves is by the valve's flow-control element design.
How do you calculate the percent opening of a control valve?
Therefore Δq/q = 8/8 = 1 and the percentage change is 100% (Δq/q×100) at x = 0,5. For an equal percentage valve, the percentage change in flow rate when the valve opens from 50% to 60%, (Δx = 0.1) must be equal to the percentage change in flow rate when the valve opens from 60% to 70% (the same Δx of 0.1).
What is Cv value of control valve?
Valve Flow Coefficient (Cv) is the flow capability of a control valve at fully open conditions relative to the pressure drop across the valve. It is defined as the volume of water (GPM in the US) at 60°F that will flow through a fully open valve with a pressure differential of 1 psi across the valve.
What are the three types of valve control?
There are three primary types of control valve trim: Snap Trim (also referred to as Quick-Opening trim) Nominal Trim (also referred to as Linear trim) Equal Percentage Trim.
What are the two types of flow control?
There are two ways to control the flow of data: Stop and Wait Protocol. Sliding Window Protocol.
Does flow control valve affect pressure?
Flow-control valves include simple orifices to sophisticated closed-loop electrohydraulic valves that automatically adjust to variations in pressure and temperature. The purpose of flow control in a hydraulic system is to regulate speed.
How do you calculate the percent opening of a control valve?
Therefore Δq/q = 8/8 = 1 and the percentage change is 100% (Δq/q×100) at x = 0,5. For an equal percentage valve, the percentage change in flow rate when the valve opens from 50% to 60%, (Δx = 0.1) must be equal to the percentage change in flow rate when the valve opens from 60% to 70% (the same Δx of 0.1).
How do you calculate the Cv of a control valve?
The equation for calculating the valve flow coefficient is Cv = Q √ (SQ/P).
How is control valve authority calculated?
Mathematically it is easy to see how, as the authority of a control valve is defined as: N = DPv / (DPv + DPc). Where: DPv = Pressure drop across a fully open control valve DPc = Pressure drop across the remainder of the circuit.
What is meant by valve sizing?
This measure of valve performance is called flow capacity or flow coefficient, symbolized as Cv. A greater flow capacity value represents a less restrictive (less “resistive”) valve, able to pass greater rates of flow for the same pressure drop.
How to Choose a Control Valve?
There are many types of valves available, each having its advantages and limitations. The basic requirements and selection depend on their ability to perform specific functions such as:
What are the factors that must be considered when choosing a control valve?
When choosing a control valve for a process, there are many things that must be considered, including the valve’s flow characteristic, its size, noise, the potential for cavitation or flashing damage, body and trim materials, actuator size and type, and its dynamic response to changes in the control signal.
What is a ball valve?
Ball valves are quick opening valves that give a tight shutoff. When fully open, a ball valve creates little turbulence or resistance to flow. Ball valves are considered high recovery valves, having a low-pressure drop and relatively high flow capacity.
What is valve actuator?
A valve actuator is a device that produces force to open or close the valve utilizing a power source.
What is the effect of globe and seat on valves?
The globe and seat construction gives the valve good flow regulation characteristics. Turbulent flow past the seat and plug, when the valve is open, results in a relatively high-pressure drop, limited flow capacity, and low recovery.
What is the best valve for a larger line?
The butterfly valve is an economical choice for larger line sizes (i.e. 8″ and above).
What is butterfly valve?
Butterfly valves consist of a disc attached to a shaft with bearings used to facilitate rotation. These are considered high recovery valves since only the disc obstructs the valve flow path. The flow capacity is relatively high and the pressure drop across the valve is relatively low.
What is a globe valve?
A globe control valve is frequently considered the ‘gold standard’ of control valves ( Figure1). They were the first modern control valves, and over the past century have been refined and modified to work in some of the toughest services. Some form of globe valve will get the job done in almost all cases. They're particularly well suited for high-temperature, high-pressure-drop applications where long, constantly bending flow paths cause continuous loss of pressure and reduced pressure recovery, minimizing noise generation and cavitation.
Is control valve technology one size fits all?
Selecting the appropriate control valve technology doesn't fall into the one-size-fits-all category. The process to be controlled has an influence on the best choice of valve. So too does the level of control accuracy required to meet the needs of the process.
Why are globe valves good?
Globe valves are a good choice for general and high differential pressure applications. One reason is because of their inherent resistance to cavitation. Changing the valve’s trim is easy, which is especially helpful if process conditions change quickly or plant capacity increases.
What is segment valve?
Segment valves are also excellent options for fibrous and unclean flow mediums. Eccentric rotary plug valves are a compact and reliable solution for general and even more demanding applications. These valves are widely used in refineries and petrochemical plants, as they can also handle dirty fluids with particles.
What is butterfly valve?
Butterfly valves are lightweight, economical solutions and are especially attractive valve solutions in large sizes. They typically offer high flow capacity and good emissions performance. Ball valves are rugged constructions that can be considered problem solvers when it comes to specific control applications.
Is a globe valve good for differential pressure?
Each type of valve plays a specific role. So it’s important to know which one to choose for the task at hand. Globe valves are a good choice for general and high differential pressure applications.
What is flow control valve?
In hydraulics, flow control valves are used to control the amount of oil supplied to various parts within a hydraulic system. In this way, the momentum of a cylinder or the rotational speed of a hydraulic motor can be controlled.
How does a valve control oil flow?
The valve controls the flow of the oil in a pipe by moving a flat plate called a gate or disc valve. Gate is built perpendicular to the length of the pipe with the help of a handwheel.
How does a globe valve work?
Unlike the other types that are straight-through valves, these valves produce slightly high-pressure drops. The closure in a globe valve is opened by means of a plug that covers a flat bottom and is then lowered onto a horizontal seat in the center of this valve. The plug in the globe valve lifts when the user opens it, and this allows the fluid to flow.
Why are globe valves used?
Globe valves are used for throttling applications because the disc of the valve can be completely removed from the flowline and are also capable of closing the flowline completely.
What is a plug valve?
As the name suggests, this valve is having a plug. This plug can be turned to move its ports to control the flow of oil and it features to reduce the friction between the plug face and the body seat when the turning of the plug.
What is a valve handwheel?
It is a common type of valve actuator. A valve handwheel is used to manually control the opening and closing of the valve.
What is a pressure compensation valve?
The pressure compensation flow valve provides a uniform volume flow rate independent of the pressure drop across the valve. On the other hand, the non-pressure-compensated valves have a variable flow rate that changes as the pressure in the valve fluctuates.
What is a control valve?
August 26, 2019. Control valves play an important role in various process industries. They are designed to control the flow of fluids in a system. They are designed to start and stop as well as throttle the fluid flow to ensure efficient process operation.
What is a linear globe valve?
Linear globe valves: These valves are made of cylindrical or disk plug element, and have a spherical body and a stationary ring seat. Linear globe valves allow easy access to internal elements, and they are used to regulate the flow of a variety of fluids.
What are the different flow directions?
Types of control valve flow direction 1 Flow to Open (FTO) 2 Flow to Close (FTC)
Where should a globe valve be mounted?
The globe valve must be mounted in proper relation to the media flow as indicated by the flow direction marked on the valve body.
What is a half ball valve?
Image Courtesy: Metso. Also called half ball valve or eccentric ball valve. In certain working conditions, the double-seated ball valves are designed in a single flow direction. In the upstream side of the ball, a hole is drilled for the pressure relief side.
What is the FTO type of flow?
When the fluid flows pass through and faces the plug directly, it gives an opening act to the plug. This is called a flow to open (F TO) type of flow direction. As the flow is upward direction on the plug, it requires higher closing torque and less opening torque and is mainly used for high-pressure applications.
What is FTC valve?
Flow to Close (FTC) When the fluid passes on top of the plug, it gives a closing action to the plug. This is called the flow to close (FTC) type flow direction. The effects of cavitation are less and it requires more breakaway torque to open and less torque for closing the valve.
Why do you need globe valves?
For temperature application, the globe valves installed so that pressure is below the disc. This promotes smooth operation, helps protect the packing, and helps the certain amount of erosion action on the seat and disc surfaces.
Which direction does a plug flow?
As the flow is upward direction on the plug, it requires higher closing torque and less opening torque and is mainly used for high-pressure applications.
