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Showing posts with the label Control Valves

Different Types of Valves multiple choice questions

  Different Types of Valves 1. In which of these treatment systems diaphragm valves are preferred? a) Moving Bed Bioreactor(MBBR) b) Desalination c) Ultrafiltration d) Demineralisation systems Answer: Demineralisation systems 2. Which of these are usually not preferred for frequent operation? a) Ball valve b) Plug valve c) Gate valve d) Butterfly valve Answer: Gate valve 3. Which of the following valves are used in high duty cycle applications? a) Check valve b) Clapper valve c) Ceramic disc valve d) Choke valve Answer: Ceramic disc valve 4. Which valve can be used in the service to handle fluids and gases and at the same time can be used for throttling as well? a) Butterfly valve b) Gate valve c) Plug valve d) Diaphragm valve Answer: Plug valve 5. In globe valves, the flow rate control is determined by _______ a) Size of the opening b) Lift of the valve plug c) Pressure difference d) Gravity Answer: Lift of the valve plug 6. Poppet valves are used in piston engines a) True b) False An

Process Control Valves multiple choice questions

  Process Control Valves 1. What is the velocity of water from a cylindrical valve if the cylindrical valve has a diameter of 10 cm and rate of flow of water in Litres per second is 157L/s? a) 40m/s b) 30m/s c) 20m/s d) 30m/s Answer: 20m/s 2. What is the rate of flow of water in Litres per second from a cylindrical valve if the cylindrical valve has a diameter of 10 cm and velocity of water is 12m/s? a) 100L/s b) 127L/s c) 157L/s d) 94.2L/s Answer: 94.2L/s 3. How many ports does a 3 way valve have? a) 1 b) 2 c) 3 d) 4 Answer: 3 4. How many exit ports does a 2 way valve have? a) 1 b) 2 c) 3 d) 4 Answer: 1 5. What is the final amount of water flowing through a valve in one hour when originally the rate of flow from the valve was 10m 3 /hr which was reduced by 80%? a) 3m 3 /hr b) 4m 3 /hr c) 5m 3 /hr d) 2m 3 /hr Answer: 2m 3 /hr 6. What is the percentage change in amount of water flowing through a valve in one hour when originally the rate of flow from the valve

Control Valve multiple choice questions

  Control Valve 1. The definition of split range control valves implies that they are a) calibrated with complementary ranges. b) easily re-ranged for different characteristics. c) equipped with quick-acting positioners. d) only used in sets of three. Answer: calibrated with complementary ranges. 2. The proper “fail safe” status of a valve should always be dictated by a) economic savings b) the nature of the process c) the controller’s tuning d) the controller’s action (direct or reverse) Answer: the nature of the process 3. Calculate the necessary Cv rating for a liquid service valve, given a pressure drop of 24 PSID, a specific gravity of 1.3, and a maximum flow rate of 140 GPM. Assume there will be no flashing or choked flow through the valve. a) 0.1319 b) 32.58 c) 7.583 d) 2585 Answer: 32.58 4. When a valve is installed in a process with where the differential pressure (drop) across the valve decreases with increasing flow, the best trim characteristic to choose for the valve would

Diaphragm Valves

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  Diaphragm Valves Diaphragm valves get their name from a flexible disc which comes into contact with a seat at the top of the valve body to form a seal. A diaphragm is a flexible, pressure responsive element that transmits force to open, close or control a valve. Diaphragm valves are related to pinch valves, but use an elastomeric diaphragm, instead of an elastomeric liner in the valve body, to separate the flow stream from the closure element. A diaphragm valve is a linear motion valve that is used to start, regulate, and stop fluid flow. The name is derived from its flexible disk, which mates with a seat located in the open area at the top of the valve body to form a seal. A diaphragm valve is illustrated in below Figure. Diaphragm valves are, in effect, simple “pinch clamp” valves. A resilient, flexible diaphragm is connected to a compressor by a stud molded into the diaphragm. The compressor is moved up and down by the valve stem. Hence, the diaphragm lifts when the compressor is

What is Air-operated valves and how does an air operated valve work?

  Air-operated valves Air-operated valves is Opening and shutting take place with the power of air pressure An air-operated valve is a type of power operated valve that uses air pressure against a piston or diaphragm to produce linear or circular movement to operate a valve. Types are 2-way, 3-way and 4-way. The 2 way air-operated valves can be either normally closed or normally opened. Modulating control valves each with 4-20mA I to P converter linked to pneumatic a valve positioner controlling a diaphragm actuator What is an air operated valve? An air operated valve, also known as an angle seat valve is a vital component for any pneumatic circuit. The valve works to direct or block airflow, controlling the speed or sequence of operations, promoting the effective functionality of a component or piece of machinery. Air operated valves are available as either a normally open or normally closed valve, the components work to control the process of media through a valve. An air operated va

Control Valve Fail Safe Action

  Control Valve Fail Safe Action Loss of instrument air supply pressure Loss of electrical power There are four choices as to control valve “response” to the emergency condition  Fully Close Fully Open In Last Position Continue Throttling For either fail-safe loss of Instrument Air Supply or loss of electrical power, it is the actuator’s benchset range spring that “drives” the control valve’s plug to its fail-safe open or closed position. Loss of Instrument Air Supply Pressure Fully Close The actuator’s benchset range spring “drives” the valve plug “closed” when loading air pressure goes towards or near 0 psig. (Air to Open Fail Close “Reverse”) Because Instrument Air Supply piping systems can be extensive (big), the Instrument Air Supply can decay too slowly causing operational problems. In such cases it may be desirable to use a 3-way pilot switching valve to “anticipate” the eventual loss of Instrument Air Supply and quickly stroke the control valve to its fail-safe position, elimin

Comment on fail safe action i.e Air to Open (ATO) and Air to Closed (ATC) of control valve.

  Comment on fail safe action i.e Air to Open (ATO) and Air to Closed (ATC) of control valve. Air to Open (ATO) of Control Valve (Failure Close (FC) - Air to Open) The actuator's benchset range spring "opens" the valve plug when the loading air pressure drops to or near 0 psig. (Air to Closed Fail Open “Direct”) Same scheme as I.a. A back to air to closed fail open arrangement can be applied to a fail open control valve to eliminate transient effects. Fail close means the valve will close when the signal is interrupted or lost. This is the opposite of the above scenario. Since air pressure is required to keep the valve open, it will automatically close when the power goes out because there is no longer a working air source. Actuated or automatic valves that return to a pre-set position after removal of actuating force are called "fail-safe" valves. The most common type is "fail-safe normally-closed." On the other hand, "fail-safe normally-open&quo

difference between a double seated and single seated globe valves

  Double Seated and Single Seated What is the difference between a double seated and single seated globe valves. Single seated globe valves Large amount of force required to drive the stem Double seated globe valves Stem can be driven with small amount of force Single seated globe valves Tight shut off  Double seated globe valves Can not achieve perfect closure resulting in leakage  Single seated globe valves Used in small diameter applications Double seated globe valves Used in larger diameter applications  Single seated globe valves Used for controlling large range of process parameters hence used in oil and gas production, power generation Double seated globe valves Used for high flow and high pressure services Single seated globe valves Single seated valves are used in case of higher shut-off and the pressure range is low compared to a double-seated valve. Double seated globe valves Double seated valves are pressure balanced and can be used for high-pressure applications. Single se

Hydraulic Actuator System working principle

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Hydraulic Actuator System Operating Principle of Hydraulic Actuator System Hydraulic actuator system uses the concept proposed by Pascal generally known as Pascal’s Law or Pascal’s Principle. Pascal’s Law states that the pressure applied at a specific point to a confined fluid in a container is transmitted equally in all the directions within the fluid as well as the walls of the container without any loss. Suppose, if pressure P is applied to an area A, then the resultant force due to an applied pressure will be F = P * A Now, if a certain force F is applied in a smaller area to have pressure P in a confined fluid, then the force produced on a larger area as a result of it can be comparatively larger than the force created by the pressure. In this way, the applied pressure at a certain point is used to generate very large forces and this principle is utilized by various hydraulic systems. Working of Hydraulic Actuator The figure below represents the schematic representation of the hyd

Diaphragm Valves Construction

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  Diaphragm Valves Construction The operating mechanism of a diaphragm valve is not exposed to the media within the pipeline. Sticky or viscous fluids cannot get into the bonnet to interfere with the operating mechanism. Many fluids that would clog, corrode, or gum up the working parts of most other types of valves will pass through a diaphragm valve without causing problems. Conversely, lubricants used for the operating mechanism cannot be allowed to contaminate the fluid being handled. There are no packing glands to maintain and no possibility of stem leakage. There is a wide choice of available diaphragm materials. Diaphragm life depends upon the nature of the material handled, temperature, pressure, and frequency of operation. Some elastomeric diaphragm materials may be unique in their excellent resistance to certain chemicals at high temperatures. However, the mechanical properties of any elastomeric material will be lowered at the higher temperature with possible destruction of t

Diaphragm Valves construction types and applications

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  Diaphragm Valves Diaphragm valves get their name from a flexible disc which comes into contact with a seat at the top of the valve body to form a seal. A diaphragm is a flexible, pressure responsive element that transmits force to open, close or control a valve. Diaphragm valves are related to pinch valves, but use an elastomeric diaphragm, instead of an elastomeric liner in the valve body, to separate the flow stream from the closure element. A diaphragm valve is a linear motion valve that is used to start, regulate, and stop fluid flow. The name is derived from its flexible disk, which mates with a seat located in the open area at the top of the valve body to form a seal. A diaphragm valve is illustrated in below Figure. Diaphragm valves are, in effect, simple “pinch clamp” valves. A resilient, flexible diaphragm is connected to a compressor by a stud molded into the diaphragm. The compressor is moved up and down by the valve stem. Hence, the diaphragm lifts when the compressor is

Globe Valve parts, types, advantages, disadvantages and applications

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  Globe Valve Globe valves are named for their spherical body shape with the two halves of the body being separated by an internal baffle. This has an opening that forms a seat onto which a movable plug can be screwed in to close (or shut) the valve. The plug is also called a disc or disk. In globe valves, the plug is connected to a stem which is operated by screw action using a handwheel in manual valves. Typically, automated globe valves use smooth stems rather than threaded and are opened and closed by an  actuator assembly.  What is Globe Valve ? A globe valve is a linear motion valve used to stop, start, and regulate fluid flow. A Z-body globe valve is illustrated in below Figure. The globe valve disk can be totally removed from the flow path or it can completely close the flowpath. The essential principle of globe valve operation is the perpendicular movement of the disk away from the seat. This causes the annular space between the disk and seat ring to gradually close as the val

Angle seat piston valves working principle and application

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  Angle seat piston valves An angle seat piston valve is a pneumatically-controlled valve with a piston actuator providing linear actuation to lift a seal off its seat. The seat is set at an angle to provide the maximum possible flow when unseated. Angle seat piston valves are particularly suited to applications where high temperatures and large flow rates are required, such as steam or water. When used in reverse some models of angle seat piston valve will eliminate water hammer when operated. Working Angle seat valves are 2/2-way pneumatically actuated piston valves. The piston actuator provides a linear motion to lift the seal off its seat. Because the seat is positioned under an angle, the flow is minimally impeded in the open position, resulting in an excellent flow rate and a low pressure loss. They are used to regulate the flow of liquids, gases, steam, vacuum and even aggressive fluids. They can also operate with high temperatures and high viscosity media, even under zero di

What is Angle Valves and Use in Industry

  Angle Valves Angle Valves uses a linear motion to move a closure member into and out of a seating surface. Angle valves are commonly used in boiler feedwater and heater drain service and in piping schemes where space is at a premium and the valve can also serve as an elbow. The valve can have cage-style construction or expanded outlet connections, restricted trim, or outlet liners for reduction of erosion, flashing, or cavitation damage. What Is an Angle Valve? An angle valve has an inlet and an outlet port which are perpendicular to each other. It is sorted as the manual valves and it is usually used to prevent or control the flow of a liquid in a pipe and this is the reason for it is sometimes called simply as stop valve. Stop valves are valves that entirely stop the flow of the liquid inside the pipe. But angles are mostly used as regulating device in residential plumbing and industry. Angle stops usually have an oval knob or twist handle. In public places where vandalism or steal

Control Valve Packing

  Valve Packing Most valves use some form of packing to prevent leakage from the space between the stem and the bonnet. Packing is commonly a fibrous material (such as flax) or another compound (such as teflon) that forms a seal between the internal parts of a valve and the outside where the stem extends through the body. Valve packing must be properly compressed to prevent fluid loss and damage to the valve’s stem. If a valve’s packing is too loose, the valve will leak, which is a safety hazard. If the packing is too tight, it will impair the movement and possibly damage the stem.

Control Valve Actuator

 Valve Actuator The actuator operates the stem and disk assembly. An actuator may be a manually operated hand wheel, manual lever, motor operator, solenoid operator, pneumatic operator, or hydraulic ram. In some designs, the actuator is supported by the bonnet. In other designs, a yoke mounted to the bonnet supports the actuator. Except for certain hydraulically controlled valves, actuators are outside of the pressure boundary.Yokes, when used, are always outside of the pressure boundary.

Control valve Stem

  Stem The stem, which connects the actuator and disk, is responsible for positioning the disk. Stems are typically forged and connected to the disk by threaded or welded joints. For valve designs requiring stem packing or sealing to prevent leakage, a fine surface finish of the stem in the area of the seal is necessary. Typically, a stem is not considered a pressure boundary part. Connection of the disk to the stem can allow some rocking or rotation to ease the positioning of the disk on the seat. Alternately, the stem may be flexible enough to let the disk position itself against the seat. However, constant fluttering or rotation of a flexible or loosely connected disk can destroy the disk or its connection to the stem. Two types of valve stems are rising stems and non-rising stems. These two types of stems are easily distinguished by observation. For a rising stem valve, the stem will rise above the actuator as the valve is opened. This occurs because the stem is threaded and mated

Control valve Disk and Seat

  Disk and Seat For a valve having a bonnet, the disk is the third primary principal pressure boundary. The disk provides the capability for permitting and prohibiting fluid flow. With the disk closed, full system pressure is applied across the disk if the outlet side is depressurized. For this reason, the disk is a pressure-retaining part. Disks are typically forged and, in some designs, hard-surfaced to provide good wear characteristics. A fine surface finish of the seating area of a disk is necessary for good sealing when the valve is closed. Most valves are named, in part, according to the design of their disks. The seat or seal rings provide the seating surface for the disk. In some designs, the body is machined to serve as the seating surface and seal rings are not used. In other designs, forged seal rings are threaded or welded to the body to provide the seating surface. To improve the wear-resistance of the seal rings, the surface is often hard-faced by welding and then machini

Control Valve Trim

  Valve Trim The internal elements of a valve are collectively referred to as a valve’s trim. The trim typically includes a disk, seat, stem, and sleeves needed to guide the stem. A valve’s performance is determined by the disk and seat interface and the relation of the disk position to the seat. Because of the trim, basic motions and flow control are possible. In rotational motion trim designs, the disk slides closely past the seat to produce a change in flow opening. In linear motion trim designs, the disk lifts perpendicularly away from the seat so that an annular orifice appears.

Control Valve Bonnet

  Valve Bonnet The cover for the opening in the valve body is the bonnet. In some designs, the body itself is split into two sections that bolt together. Like valve bodies, bonnets vary in design. Some bonnets function simply as valve covers, while others support valve internals and accessories such as the stem, disk, and actuator. The bonnet is the second principal pressure boundary of a valve. It is cast or forged of the same material as the body and is connected to the body by a threaded, bolted, or welded joint. In all cases, the attachment of the bonnet to the body is considered a pressure boundary. This means that the weld joint or bolts that connect the bonnet to the body are pressure-retaining parts. Valve bonnets, although a necessity for most valves, represent a cause for concern. Bonnets can Complicate the manufacture of valves, increase valve size, and represent a significant cost portion of valve cost, and are a source for potential leakage.