Industrial Applications of Flow-Through Valves (Part-I)
How to Regulate the Fluid Flow using Valves?
Dr. Sharad N. Pachpute
Introduction to Valves
- Fluid mechanics plays a role to understand fluid dynamics and its motion in pipes or ducts. The fluid motion is regulated using various types of control valves. We have to understand the determination of pressure drop and fluid motions.
- Computational modeling can help to design and optimize the performance of control valves when the formulas unable to correctly determine the pressure drop
What is a valve?
- A valve is a mechanical device to control the flow and pressure within a flow system or process
- Valves are essential parts of a pipe or duct system through which fluid flow is regulated
Basic functions of valves
- Stopping and starting flow
- Reduce or increase a flow
- Controlling the direction of flow
- Regulating a fluid flow or process pressure
- Relieve a pipe system of a certain pressure
Movement of Valves
- There are many types of valve designs that are manufactured depending on the type of fluid and industrial applications
- The valves are designed to regulate the flow as per applications
- Flow control valves have the following basic parts: the body, bonnet, trim (internal elements), actuator, and packing
- Depending on the movement of the valve body, the valves are classified
Applications of Flow Control Valves
- These valves are generally used to dispense the contents of aerosol cans.
- Aerosol valves consist of two primary components: the housing and the stem.
- Key specifications are types of application, actuator type, output type, valve size, and materials of construction.
- Application of Aerosol valves for spray
- Media of dispensed: liquids, gases, cleaning agents, creams and ointments, and any other product that is packaged in an aerosol can.
Air Logic Valves
- Air Logic Valves are widely used in pneumatic systems
- These valves are either mechanical or electro-mechanical type which is designed to control the flow of air
- They can be used where the electrical control in instances like hazardous situation
- Key design parameters: actuator type, number of ports, materials, switching speed, port thread size, pressure loss
- Air logic control valves are widely used in pneumatic systems
- Balancing valves control fluid flow by dividing flow. They can regulate the flow in pipes with Multiple flow branches
- Major design specifications are valve size, port connections, number of ports, materials , and pressure drop
- Applications of balancing valves are in HVAC applications and fluid power systems.
- Globe Valve uses a globe-shaped disc that controls the flow by closing against a restricted orifice plate.
- Key specifications include valve type, port configuration, port connections, valve size,materials of valve body
- Globe valves are used to shut off and regulate the fluid flow in wastewater plants, chemical and food processing industries,
- The Z-style valve is a commonly used globe valve
- The shape of the disc can be modified to produce a valve that can properly regulate flow.
- Globe valves can restrict the fluid flow depending on the requirements of the installation
- A typical Z-shape globe valve
- Ball Valves have quarter-turn valves which incorporate ported spheres that can swivel in the pipe stream to regulate the fluid flow
- Ball valves are useful to shut off the flow from a compressed-air line at high-pressure
- The advantage of ball valves are low head loss and better sealing
- Blind Valves ( Line blind valves) are used to stop the fluid flow through a pipeline or ducts
- They are used majorly in oil and gas industries for isolating the sections of a pipeline. Blind valves are also used on ships and offshore platforms
- Blind valves can provide a visible, immediate indication as to whether a pipe is open or closed and are used to isolate portions of a pipeline to allow maintenance.
- Blind valves and its fitting on pipes
- Butterfly Valve is a quarter-turn valve which uses centrally mounted circular flaps that swing into, and out of, the flow stream
- Key design parameters are port connection, valve size, seal, disc, seat, stem packing, and valve body
- Butterfly valves are widely used in wastewater plants, power plants, and process industries for shut-off and for regulating and isolating services. They are installed with large size pipelines.
- These valves can be difficult to operate flow at high pressure. They can be leak-prone and results in higher pressure losses
- Cock Valves are used for draining tanks and it incorporates a threaded means for opening and closing
- They are also used as low-pressure shut-offs where they typically use a quarter-turn lever.
- Major design parameters are valve type, port connections, valve size, and materials of construction
- Application of cock valve: radiators, heaters, tanks, boilers, laboratory glassware, air systems, tanks and drums
- Engine valves are used in IC engines to control flow between the combustion chamber and inlet or exhaust duct
- Key design specifications for valves are type of application, head and stem diameter, and the material.
- The opening and closing of engine valves are controlled using a mechanism of cams and springs
- They are employed in IC engines of automobiles, trucks, motorcycles
- Diaphragm valves use flexible membranes to close off flow in pipes.
- Similar to pinch valves, the diaphragm completely seals off the actuating means from the process fluid
- Major specifications are valve size, media, seal, port configuration and port connections,
- Applications of these valves are majorly in the pharmaceutical, cosmetics, food, and semiconductor industries
- The flow through a diaphragm valve is regulated with a membrane of rubber
- Disc Valves are used to control fluid flow through a pipe or duct.
- It consists of a round flat plate mounted to the end at 45 degrees to the longitudinal axis of pipe
- Rotating the stem through a half-circle opens or closes the pipe.
- Applications of disc valves are found in food processing applications
- They are also used in pharmaceutical and dairy industries to shut-off liquid, powder, or food slurries because of sanitation of liquid
Check (non-return) Valves
- Check Valves allow the fluid to flow through a pipe in one direction only
- Lift-type check valves are similar to globe valves in construction, it uses a ball or piston, often backed by a spring that opens under a specified pressure but closes as the pressure decreases, thus preventing backflow
- Swing type check valves are more suitable for pipelines with high-pressure applications
- Spring-loaded Valves are effective in low-pressure applications
- Rubber type check valves are also available which includes the rubber flap
- Application of Check valves: gas lines, for air service, and with pump
- Spring type Check valve
- Swing type Check valve
Christmas Tree Valves
- Christmas Tree Valves are used for controlling the flow of media coming from wells or other systems
- They are typically mounted to the head of the well for shutoff or controlling the flow
- Key design specifications are types application, number of ports, and pressure and temperature ratings
- Application of Christmas tree valves: oil and gas well, water injection well, water disposal well, gas injection well, condensate well and other types of wells
- Flanged Christmas tree valve
- Application Christmas tree valve over an oil wellhead
- Faucet Valves are useful for controlling fluid flow into basins or sinks and typically lack outlet connections
- They are equipped with threads for connecting hose, often called a hose bibb or spigot
- Faucet valves are commonly used in laboratories, on drums, as hose bibbs,
- Float valves use hollow spheres or other shapes mounted on levers or tracks which open and close fluid inlets.
- It is used mainly for maintaining fluid in a tank at a specific level
- Float valves are widely used in bathroom toilets or sanitary rooms to replenish the water level after a flushing the water from a small water tank
- Gate Valves are used mainly for blocking fluid flow and are less likely to be employed for flow regulation.
- A gate valve uses a plate-like barrier that can be lowered into the flow stream to regulate the flow.
- Its operation is similar to that of a globe valve except the gate provides less flow restriction than with a globe-valve plug when the valve is in the fully opened position.
- Plugs generally seal both the up and downstream sides of the valve, but plates are used to seal on the upstream face of control valve
- Gate valves has low head loss when open compared to globe valves, they are not suitable for throttling and may not produce the positive shut-off that globe valves provide.
- Gate valves are generally designated as rising-stem and non-rising stem designs.
- The major advantage of rising-stem gate valves is that they allow easy visualization and inspection in order to check the valve is closed or open
- Gate valves are widely used in wastewater plants, power plants, and process industries for shut-off the flow in pipelines
Double Block and Bleed Valves
- These valves can be mechanical or electro-mechanical devices and consist of dual inline blocker valves and single bleeder valves in common valve
- DBB valves are used mainly in process control applications for the purpose of shutting off the upstream pressure and bleeding off the fluid and/or pressure of the system.
- Cartridge Valves are used to control flow in hydraulic and pneumatic fluid power systems
- Casing Valves are used exclusively by the oil and gas industry to provide access to well casings
- Key design parameters are the type of application, actuator type, valve size, port connections and materials of construction
Other Flow Control Valves
- Depending on applications, the flow control valves are designed and customized
Major Issues in Control valves
Hydraulic Shock (Water hammer)
- Hydraulic shock in the valve is a pressure surge or wave caused when a fluid with high velocity is forced to stop or change direction suddenly (momentum change)
- A water hammer generally observes when a valve closes suddenly. It results in a pressure wave that propagates in the downward of pipe
- Excessive hydraulic shocks can lead the damage of piping system when a high velocity liquid flow is suddenly stopped with a control valve
- It is also called water hammer
Major Reasons of Water Hammer
- Insufficient bracketing of pipe work within concealed pipe ducts
- Defective control valves
Methods to Reduce Water Hammer
- Reduce supply pressure at inlet the valve using pressure reduction valves
- Connect water hammer arrestors with pipe to mitigate the shock waves.
- Check pipework is properly fixed within cavities and ducts
- Insulated or preferred pipe material can be to reduce water noise through pipe
- Replace old or defective valves
Scope of CFD Modeling for Design of Flow Valve
- Computational flow modeling is helpful to predict the pressure drop across the control valves. The pressure drop should be minimum. Flow should flow smoothly without creating much back-pressure.
- CFD modeling of valves is carried out to design and optimize the performance of control valves when the correlations cannot correctly estimate the pressure drop
- For different industrial applications, the effect of valve opening can be optimized in order to minimize the pressure drop.
- The following figure shows the CFD model of pressure relief control valve for airflow
- Velocity and pressure contours across the section of the pressure relief valve is shown below based on numerical simulation
- Click here: CFD modeling of flow through different control valves using ANSYS CFD tools
- Flow control valves have a lot of industrial and domestic applications to control the flow rate
- The best control is one that can provide the lowest pressure drop, no leakage of fluid, efficient and smooth operation
- CFD modeling is useful to evaluate the performance of flow control valves