Plenty Global
What is Valve?
Chances are there that you already know this. But there is no harm to refresh the memory.
A valve is a device that regulates, controls, or directs the flow of a fluid by opening, closing, or partially obstructing fluid flow. A sound bit complicated? Ok, let me further simplified this. A valve is a mechanical device that controls the flow and pressure of fluid within a system or process. So basically, it controls flow & pressure.
Types of Valves
In piping following types of valves are used depending on the requirements. The cost of Valve in the piping system is up to 20 to 30% of the overall piping cost. And the cost of a given type and size of the valve can vary 100%. It means that if you choose a ball valve over a butterfly valve for the same function. It can cost you more. So, the selection of valves is essential to the economics, as well as operation, of the process plants
Gate Valve
What is Gate Valve?
A gate valve can be defined as a type of valve that used a gate or wedge type disk and the disk moves perpendicular to flow to start or stop the fluid flow in piping.
A gate valve is the most common type of valve used in any process plant. It is a linear motion valve used to start or stop fluid flow. In service, these valves are either in a fully open or fully closed position.
When the gate valve is fully open, the disk of a gate valve is completely removed from the flow. Therefore virtually no resistance to flow. Due to this very little pressure drops when fluid passes through a gate valve.
To achieve proper sealing, when the valve is fully closed, 360° surface contact is required between disk and seats.
Gate valves should not be used for regulation or throttling of flow because accurate control is not possible. The high velocity of the flow in the partially open valve may cause erosion of the disc and seating surfaces and also creates vibration and noise.
Here you can see the main parts of the gate valve. The disk of a gate valve is also known as a wedge.
Types of Gate Valves
There are three ways to classify the gate valve.
Solid Wedge Gate Valve
Solid wedge is the most common & widely used disk type because of its simplicity and strength. A valve with a solid wedge may be installed in any position, and it is suitable for almost all fluids. It can be used in turbulent flow also.
However, it does not compensate for changes in seat alignment due to pipe loads or thermal expansion. So, this type of disk design is most susceptible to leakage. Solid wedge is subjected to thermal locking if used in high-temperature service.
Thermal locking is a phenomenon in which wedge is stuck between the seats due to the expansion of the metal. Solid-wedge gate valves are generally used in moderate to lower pressure-temperature applications.
Flexible Wedge Gate Valve
The flexible wedge is a one-piece solid disk with a cut around the perimeter. These cuts vary in size, shape, and depth. A shallow, narrow cut on wedge perimeter gives less flexibility but retains strength. A cast-in recess or deeper and wider cut on wedge perimeter gives more flexibility but compromises the strength.
This design improves seat alignment and offers better leak tightness. It also improved performance in situations where thermal binding possible. Flexible wedges Gate valves are used in steam systems.
Thermal expansion of the steam line sometime causes distortion of valve bodies which may lead to thermal blinding. The flexible gate allows the gate to flex as the valve seat compresses due to thermal expansion of the steam pipeline and prevents thermal blinding.
The disadvantage of flexible gates is that line fluid tends to collect in the disk. These may result in corrosion and ultimately weaken the disk.
Split wedge or Parallel disks Gate Valve
Split wedge Disk consists of two solid pieces and holds together with the help of a special mechanism. You can see the same in images. In case, one-half of the disk is out of alignment; the disk is free to adjust itself to the seating surface. The split disk can be in a wedge shape or a parallel disk type.
Parallel disks are spring-loaded, so they are always in contact with seats and give bi-directional sealing. The split wedge is suitable for handling noncondensing gasses and liquids at normal and high temperatures.
Freedom of movement of the disk prevents thermal binding even though the valve may have been closed when a line is cold. This means when a line is get heated by fluid and expand it does not create thermal blinding.
Types of gate valve based on body, bonnet connection
1st is screwed bonnet: This is the simplest design available and it is used for inexpensive valves.
2nd is bolted-bonnet: This is the most popular design and used in a large number of gate valves. This requires a gasket to seal the joint between the body and bonnet.
3rd is Welded-Bonnet: This is a popular design where disassembly is not required. They are lighter in weight than their bolted-bonnet counterparts.
4th one is Pressure-Seal Bonnet: This type is used extensively for high-pressure high-temperature applications. The higher the body cavity pressure, the greater the force on the gasket in a pressure -seal valve.
OS & Y Gate Valve or Rising Stem (Outside Stem and Screw Type)
For a rising stem valve, the stem will go up while opening the valve and move down when you close the valve. You can see in the image. In inside screw design, the threaded portion of the stem is in contact with the flow medium, and when you open the valve, handwheel rise with the stem.
Whereas in the case of outside screw design, the only smooth portion is exposed to the flow medium and the stem will rise above the handwheel. This type of valve is also known as OS & Y valve. OS & Y means outside steam and York.
Non-rising Stem Gate Valve or Insider Screw Valve
There is no upward movement of the stem in a non-rising stem type. The valve disk is threaded internally. The disc travels along the stem like a nut when the stem is rotated. You can see the image. In this type of valve, stem threads are exposed to the flow medium.
Therefore, this design is used where space is limited to allow linear stem movement, and the flow medium does not cause erosion, corrosion, or wear and tear to stem material. This type of valve also known as an insider screw valve.
Gate Valve Applications
Advantages of Gate Valve
Attention
Ball Valve
A Ball valve is a quarter-turn rotary motion valve that uses a ball-shaped disk to stop or start the flow. It resembles a plug valve in many ways. When a port in the ball is in line, it allows flow whereas when you rotate the valve 90 degrees, solid part of the ball stop the flow.
Most ball valves are of the quick-acting type, which requires a 90° turn of the valve handle to operate the valve. But in case large size valve which required considerable force to open or close the valve, the gear-operated actuator is used. With this arrangement, a small handwheel is enough to operate a fairly large valve.
In this article, I have covered following types of Ball Valves that used in piping.
Floating Ball Valve
In a floating ball valve, the ball is held in the position by the compression of the two elastomeric seats against the ball. The ball is free to float inside the valve body. See the highlighted portion in the image and remember as you will see the difference when I will explain to you about the trunnion mounted valve.
The stem is connected to a slot at the top of the ball which allows the ball to rotate a quarter turn (90 degrees). The shaft allows for a certain amount of lateral movement of the ball that is generated from the upstream pressure acting on the ball. This small lateral movement, in fact, produces a load on the ball that presses it against the downstream seat which improves leak tightness of valve. This type of valve design is capable of bi-directional shut-off. The floating valve is very difficult to operate when upstream pressure is high. You can see the image of a floating type valve.
Trunnion Mounted Ball Valve
Trunnion mounted valve is a solution to the problem of excessive torque required by a floating type valve in high-pressure service. A short shaft like an extension which is known as a trunnion set in the body. You can see this in the image. In this design steam and ball work as a single unit. The ball is supported by two floating or spring-loaded seats that remain in constant contact with the ball.
Trunnion ball design required a lower operating torque. Hence, reduces the size of the actuator and overall costs of the valve. This cost difference becomes an important factor when the pressure class and valve size increases. Check the video below for an animation of this type of valve.
Depending on your requirements, you can arrange the port of valve in the three-way.
Three patterns are available. Venturi port type, full port type, and reduced port type. The full-port ball valve has an inside diameter equal to the inside diameter of the pipe. This design allows pigging. In the venturi and reduced-port types, the port is generally one pipe size smaller than the line size.
The ball type disc can be a free float or fixed in the valve body. A free-floating valve is known as a floating type whereas a fixed type valve is known as a trunnion mounted valve.
Types of Ball Valves based on Body Construction
Ball valves are manufactured in different body arrangements. Based on this valve can be classified in the following ways
For Extremely high pressure and temperature services, the full welded body is also used.
Top-Entry Ball Valve
As you can see in the image above, removing bonnet cover of top entry valves, allows access to valve internals for assembly, disassembly, repair, or maintenance without removing the valve from the pipeline.
Split-Body Ball Valve
In this design, a valve body is divided into two or three body parts. A ball, seat rings, stem, and other internals set inside the larger body part and held together with smaller parts by bolting.
For a split body, two pieces valve, refer floating ball valve image. Refer below image for split body three pieces type valve.
Ball Valve Parts
Major components of the valve are the body, spherical ball, steam, and seats. It can be metal seated or soft seated. This valve may be unidirectional, bidirectional, or multidirectional, depending on the number of valve ports and the number of valve seats. Same as multiport plug valve. In the image below, you can see the 3-way ball valve.
Applications of the Valve
Advantages
Attention
Glob valve
What is Globe Valve?
A globe valve is a linear motion valve used to stop, start, and regulate the fluid flow. The globe valve disk can be removed entirely from the flow path, or it can completely close the flow path. During the opening and closing of the valve, the disc moves perpendicularly to the seat.
This movement creates the annular space between the disk and seat ring that gradually closes as the valve closed. This characteristic provides the globe valve good throttling ability required for regulating the flow.
Leakage from the globe valve seat is less as compared to the gate valve, mainly due to right angle contact between the disc and seat ring, which allows tighter seal between seat the disk.
Globe valves can be arranged in such a way that the disk closes against the flow or in the same direction of flow.
When the disk closes in the direction of flow, the kinetic energy of the fluid helps closing but obstructs the opening. This characteristic is preferable when a quick-acting stop is required.
When the disk closes against the direction of flow, the kinetic energy of the fluid obstructs closing but helps to open the valve. This characteristic is preferable when quick-acting start is required
Globe valves can be arranged in such a way that the disk closes against the flow or in the same direction of flow.
When the disk closes in the direction of flow, the kinetic energy of the fluid helps closing but obstructs the opening. This characteristic is preferable when a quick-acting stop is required.
When the disk closes against the direction of flow, the kinetic energy of the fluid obstructs closing but helps to open the valve. This characteristic is preferable when quick-acting start is required.
Globe Valve Disk Types
Globe valve is available in many different types of disc arrangement. The most used disk designs are listed below.
The ball disk design is used in low-pressure and low-temperature systems. It is capable of throttling flow, but in principle, it is used to stop and start the flow.
Needle disk design provides better throttling as compared to ball or composition disk design. A wide verity of long and tapered plug disks are available to suit different flow conditions.
Composition disk is used to achieve better shutoff. A hard, non-metallic insert ring is used in composition disk design.
Types of Globe Valve
Depending on the type of body there are three types of globe valves
Z types Globe Valve
The simplest design and most common type is a Z-body. The Z-shaped partition inside the globular body contains the seat. The horizontal seating arrangement of the seat allows the stem and disk to travel at a perpendicular to the pipe axis resulting in a very high-pressure loss.
The valve seat is easily accessible through the bonnet which is attached to a large opening at the top of the valve body. Stem passes through the bonnet like a gate valve.
This design simplifies manufacturing, installation, and repair. This type of valve is used where pressure drop is not a concern and throttling is required.
Y types Globe Valve
The Y-type design is a solution for the high-pressure drop problem in Z-type valves. In this type, seat and stem are angled at approximately 45° to the pipe axis. Y-body valves are used in high pressure and other critical services where pressure drop is concerned.
Angle types Globe Valve
Angle globe valve turns the flow direction by 90 degrees without using an elbow and one extra pipe weld. Disk open against the flow. This type of globe valve can be used in the fluctuating flow condition also, as they are capable of handling the slugging effect.
Globe Valve Types based on Body Bonnet Connection
Screwed bonnet: This is the simplest design available and it is used for inexpensive valves.
Bolted-bonnet: This is the most popular design and used in a large number of globe valves. This requires a gasket to seal the joint between the body and bonnet.
Welded-Bonnet: This is a popular design where disassembly is not required. They are lighter in weight than their bolted-bonnet counterparts.
Pressure-Seal Bonnet: This type is used extensively for high-pressure high-temperature applications. The higher the body cavity pressure, the greater the force on the gasket in a pressure -seal valve.
Application of Globe valve
Globe Valves are used in the systems where flow control is required and leak tightness is also important.
Advantages
Attention
Plug valve
What is Plug Valve?
Plug valve is a Quarter-turn rotary motion Valve that uses a tapered or cylindrical plug to stop or start the flow. The disk is in plug shape, which has a passage to pass the flow.
In the open position, this bored passage is in line with the flow. When the plug is turned 90° from the open position, the solid part of the plug blocks the flow.
It is used in place of a gate valve where the quick operation is required. It can be used in high-pressure temperature services.
Types of Plug Valves
These valves are available in either a lubricated or non-lubricated design and with different styles of port openings through the plug.
Lubricated Plug Valve
The plug inside a lubricated plug valve has a cavity in the middle along its axis. You can see this in the image. Lubricant chamber at the bottom and the sealant injection fitting at the top ensure the supply of lubricant.
The small check valve below the injection fitting prevents the sealant from flowing in the reverse direction once the sealant is injected into the cavity.
Plug surface gets constantly lubricated by the sealant that moves from the center cavity through radial holes into lubricant grooves on the plug surface. Now why we required all this? Many plug valves are of all-metal construction.
The narrow gap around the plug may allow leakage, and if you reduce the gap further, it will increase the friction and plug may get stuck inside the valve body.
The lubricant reduces the force required to open or close the valve and allows smooth movement of the plug. It also prevents corrosion of the plug.
The lubricant material must be compatible with the fluid of the pipeline. It should not dissolve or wash away by the flow medium as this could contaminate the fluid, and damage the seal between the plug and the body, resulting in leakage. Also, the sealant used must be able to withstand the temperature of the flow medium.
Lubricated plug valves are available in the large size range, and they are fit to work in high-pressure temperature services. These valves are subject to less wear and provide better corrosion resistance in some service environments.
Non-lubricated Plug Valves
A non-metallic elastomeric sleeve or liner is used in this type of valve. This sleeve is installed in the body cavity of the valve. The polished tapered plug acts as a wedge and presses the sleeve against the body.
This nonmetallic sleeve reduces the friction between the plug and the valve body. Non-lubricating plug valves required minimum maintenance. Due to the non-metallic seat, these valves are not used in high-temperature services.
Lubricating and non-lubricating valves are capable of providing a bubble-tight shutoff and are of compact size.
Multi-Port Plug Valves
Multiport valves are used in transfer lines and for diverting services. A single multiport valve may serve the purpose of three or four gate valves or other types of the shutoff valve.
However, sometimes the multiport valve does not completely shut off flow. Great care should be taken in specifying the particular port arrangement for proper operation.
Plug Valve Parts
The typical plug valve is consisting of a body, bonnet, stem, and plug. The seat is an integral part of the body in case of a lubricated type. For a non-lubricated type, a non-metallic seat is used to improve leak tightness of the valve.
Plug Valve Disk Types
Plugs are either round or taper cylinder. They may have various types of port openings, each with a varying degree of the opening area.
Plugs are available with
Rectangular, Round, and Diamond Port design.
Application of Valve
Advantages
Attention:
Butterfly Valve
A Butterfly valve is a quarter-turn rotary motion valve, that is used to stop, regulate, and start the flow. The butterfly valve has a short circular body. Butterfly Valve is suitable for large valve applications due to Compact, lightweight design that requires considerably less space, as compared to other valves.
Types of Butterfly Valves
Large Butterfly valves are usually equipped with gearbox type actuator, where the handwheel is connected to the stem via a gearbox. This will reduce the force but at the same time reduce the speed of the operation. This type of valve should be installed in the open position. If the valve is closed during installation, the rubber seat will wedge against the valve disc and make it difficult to open.
Types of Butterfly Valves Based on Body Construction
Based on the type of ends of the body butterfly valves are available in following types.
Wafer Types
The wafer body is placed between pipe flanges, and the flange bolts surround the valve body. A wafer type butterfly valve is easy to installed but it cannot be used as an isolation valve.
Lug Style
The lug body has protruding lugs in the periphery of a body that provides passage to bolt holes that match with those in the flanges.Flanged Type
In this types, the body has flanged that match with pipe flange dimension.Butt Welded Ends Types
Zero offset Butterfly Valve
Zero offset design used for the valve that used in low-pressure and temperature services. In this design, the disc and shaft axis is concentric with the valve body. In the open position, the disc divides the flow into two equal halves, with the disc in the middle and parallel to the flow.
This type of valve has a resilient seat. Sealing is achieved when the disc deforms the soft seat. There is friction between the disk and seat during the full operating cycle which is the disadvantage of zero offset valve.
Double Offset Butterfly Valve
In Double Offset, the disk is offset from the valve center line and also from valve body center line. You can see this in the image where one and two are written. This creates a cam action during operation that lifts the seat out of the seal.
Double offset makes opening and closing smooth as friction is applicable only during the first few degrees of opening and final few degrees of closing, approx 10 degrees of opening and closing.
Triple Offset Butterfly Valve
In Triple Offset design the third offset created by the geometry design of the seating surface. The seat is machined into an offset conical profile resulting in a right-angled cone. You can see this in the third image with small enlargement of seating angle.
This ensures frictionless stroking throughout its operating cycle. Contact is only made at the final point of closure with the 90° angle acting as a mechanical stop; the Metal seated valve uses triple offset design.
Seat Types
Butterfly valves can be metal-to-metal seated, soft seated, or with a fully lined body and disc. The first image is of a soft seated fully lined body and disc valve. Second, is a soft seat with metal disk and the third is metal to metal seat type valve.
The disk of butterfly valve can be concentric or eccentric with the valve body. Here I have shown three different arrangements of the disk with respect to a center of the valve body.
Applications
Advantages
Attention
Needle Valve
Needle valves are similar to a globe valve in design with the biggest difference is the sharp needle-like disk. Needle valves are designed to give very accurate control of flow in small diameter piping systems. They get their name from their sharp-pointed conical disc and matching seat.
A needle valve is a manual valve that used where continuous throttling of flow is required for regulation. Needle valves are similar to the globe valve in design with the biggest difference is the sharp needle-like disk.
Needle valves are designed to give very accurate control of flow in small diameter piping systems. They get their name from their sharp-pointed conical disc and matching seat.
Fluid flowing through the valve turns 90 degrees and passes through an orifice. Due to needle shape disk, a certain portion of the disk will pass through seat opening before disk comes in contact with the seat, which has matching tapered design as a disk. This arrangement permits a very gradual increase or decrease in the size of the opening.
Needle valve has forged and machined body. This body can be of forged carbon steel or stainless steel depending on the requirements of the services. A seat can be a soft, metal, or composite, same as a globe valve. Normally needle valves are used in smaller sizes and are provided with either screwed or socket weld end.
All the aspects of needle valve are the same as a global valve except its size and pointed needle-like disk. You can refer to a globe valve for more detail.
Needle Valve Application
Check Valve
What is a Check Valve?
The valve that used to prevent backflow in a piping system is known as a check valve. It is also known as a non-return valve or NRV. The pressure of the fluid passing through a pipeline opens the valve, while any reversal of flow will close the valve.
It allows full unobstructed flow and automatically shuts as pressure decreases. The exact operation will vary depending on the mechanism of the valve.
Types of Valves
The type of disk will decide the type of valve. Most common types of Check valves are
Swing Check Valve
The disc in a swing type valve is unguided as it fully opens or closes. This Valve operates when there is flow in the line and get fully closed when there is no flow. Turbulence and pressure drop in the valve is very low. Disk and seat designs can be of metal to metal or metal to composite.
The angle between the seat and the vertical plane is known as the seating angle and varies from 0 to 45 degrees. Usually, the seat angles are in the range of 5 to 7 degrees. Larger seat angles reduce the disc travel, resulting in quick closing, thus minimizing the possibility of water hammer. A vertical seat has a 0-degree angle.
The swing type valve allows full, unobstructed flow and automatically closes as pressure decreases. Usually installed in combination with gate valves because they provide relatively free flow combinations.
A basic swing type valve consists of a valve body, a bonnet, and a disk that is connected to a hinge.
Tilting Disc Check Valve
The tilting disc type valve is designed to overcome some of the weaknesses of conventional swing type valves. The design of the tilting disk enables the valve to open fully and remain steady at lower flow rates and close quickly when the forwarding flow stop.
The dome-shaped disc floats in the flow and fluid flow on both the bottom and top of the disk surfaces. As the disk is spring-loaded, when forward flow pressure reduces, the spring force helps the valve to close fast. In the image above, you can see the flow from the valve.
Tilting Disc type Valve is available in wafer type and lug type design.
Ball Type and Plug Type Lift NRV
The seat design of a lift Check valve is similar to a Globe valve. A piston or a ball is usually used as a disk.
Lift Check valves are particularly suitable for high-pressure service where the velocity of flow is high. The disk is perfectly set on the seat with full contact. They are suitable for installation in horizontal or vertical pipelines with upward flow.
When the flow enters below the seat, a disk is raised from the seat by the pressure of the upward flow. When the flow stops or reverses, the backflow and gravity forced the disk downward to set on the seat. Commonly used in piping systems that used globe valves as a flow control valve.
Here you can see the plug or piston type and ball type check valve. These valves provide superior leak-tight characteristics to those of swing check valves.
Some design in plug type uses spring to retain the disk in a closed position. This will ensure that the valve allows fluid flow only when there is enough pressure in the flow direction.
A ball-type valve is very simple as it simply works on the principle of gravity. When there is enough pressure in the flow, it lifts the ball upward but when pressure reduced ball roll down and closed the opening.
Dual Plate / Dual Disc Check Valve
A dual plate check valve is known as a butterfly check valve, Folding Disc Check Valves, double-disc, or splits disc check valve. As the name suggests, two halves of the disk move towards centreline with the forward flow and with reverse flow two halves open and rest on the seat to close the flow (Flapping action).
Use of Dual Plate Check Valve is popular in low-pressure liquid and gaseous services. Its lightweight and compact construction make it a preferable choice when space and convenience are important.
It is 80 to 90% lighter than the conventional full body check valve. Frequently used in systems that used butterfly valves. The cost of installation & maintenance is very low compared to other types.
Stop Check Valve
Stop Check Valve is a combination of a lift check valve and a globe valve. It can either be used as a check valve or as an isolation (stop) valve like a globe valve. These valves can be closed with the help of a stem that is not connected to the valve disc during normal operation and make it possible to use these valves as a regular NRV.
However, when needed, the stem is used to holds the free-floating disc against the valve seat, just as a globe valve. These valves are available in tee, wye, and angle patterns. Swing type and piston lift type valves are commonly used as stop check valves.
Application of Check Valve (NRV)
Check valves (Non-return valve) are used in a piping system to prevent backflow. The discharge line of rotary equipment such as pump and compressor always fitted with a check valve to prevent backflow.
Advantages
The only function of a Non-return valve is to prevent backflow. There is no better alternative. Yes, you can choose the best NRV from the various available type that you have learned but you cannot supplement the Non-return valve with another valve.
Pressure Relief Valve
A pressure relief valve is a safety device designed to protect pressurized equipment or system during an overpressure event or in the event of a vacuum.
But what is an overpressure? An overpressure event is a condition, in which pressure inside the equipment or piping system increased beyond the specified design pressure or maximum allowable working pressure (MAWP). If not relieved this pressure can damage the system, property, and personal. Similarly, an unwanted vacuum is also dangerous for the system.
The primary purpose of a pressure Relief Valve is to protect the life and property by venting fluid from an over-pressurized system. furthermore, vacuum relief valve ensures that vacuum like situation does not occur in the system by allowing air inside the system.
There are three types of pressure relief devices:
Reclosing Type Pressure Relief Valve
A reclosing-type pressure relief Valve is designed to close automatically after the relief operation. Relief valves, Safety valves, and Safety relief valves are reclosing type Pressure Relief Devices.
Relief valves
A relief valve is a gradual lift pressure relief device actuated by inlet static pressure. An opening is proportional to the increase in inlet pressure over the opening pressure of the valve.
It may be provided with an open or enclosed spring housing that also known as a bonnet. Here in the image, you can see the open spring type bonnet. The opening pressure at which valve act, can be adjusted by changing the load on spring.
Here in the image, you can see the enclosed spring type Relief valves for closed discharged applications. Relief valves are commonly used with non-compressible liquid systems in chemical, petrochemical, and oil & gas industries.
Safety valves
A safety valve is a rapid opening or pop-up action pressure relief valve actuated by inlet static pressure. Safety valves are used primarily with compressible gasses. Particularly for steam and air services.
Safety valves are classified according to the lift of the disk and bore of the valve. Types of safety valves are low lift, full-lift, and full-bore safety valves.
Safety Relief Valves
Pressure Relief Valve
The conventional pressure relief valve is characterized by a rapid pop action or by opening proportionally to the increase in pressure with respect to the opening pressure of the valve.
The main parts of the Conventional pressure relief valve are a body, bonnet, disk, disk holder, seat, and spring. Based on the seating material, conventional pressure relief valves are classified as metal seated valves and soft seated valves. See the image for clarity.
During normal operating conditions, the pressure at the inlet is below the set pressure, and the disk remains seated on the nozzle, preventing flow through the nozzle.
The working principle of a conventional spring-loaded pressure relief valve is based on the balance of force. That means the spring load will keep the disk on the seat till the system pressure is less than the spring force.
This pressure is known as set pressure. The disk remains seated on the seat in the closed position till the inlet pressure exceeds set pressure and overcome the spring force. When the inlet pressure is reduced to a level below the set pressure spring force close the valve.
Conventional pressure relief valves are used for applications where an excessive variable or built-up back pressure is not present. Back-pressure will directly affect the valve performance. A pressure built-up on the outlet side of PSV is known as backpressure. You will learn more about back pressure in the lecture on bellows type PSV.
Advantages of Conventional PRV
Attention
Vacuum Relief Valve
A simple vent can Provide protection against vacuum. Our home water storage tanks are fitted with this kind of simple vent. But in the industrial tank which stores various chemical and hydrocarbon, this simple vent may release vapor of these products in an atmosphere, which can be odorous, toxic, potentially hazardous. To avoid such release, a special vacuum relief valves are used.
Pressure Vacuum Relief Valve -PVRV
The pressure vacuum relief valve or pressure-vacuum vent, are designed to maintain a tight seal until system pressure or vacuum exceeds the set pressure of the valve. When overpressure occurs, the pressure lifts the disk just like a safety valve, allowing vapors to pass.
When a vacuum occurs, vacuum lifts the disk and lets the air inside to break the vacuum. It is like breathing of a tank. This PVRV arrangement prevents continuous vapor loss to the atmosphere as it opens only when the set pressure is reached. You can see the image for a better understanding.
Pinch Valve
The pinch valve is also known as a clamp valve. It is a linear motion valve. Used to start, regulate, and stop fluid flow. It uses a rubber tube, also known as a pinch tube, and a pinch mechanism to control the fluid. Pinch Valve is ideally suited for the handling of slurries, liquids with large amounts of suspended solids, and systems that convey solid material pneumatically.
The pinch valve is also known as a clamp valve. It is a linear motion valve. Used to start, regulate, and stop fluid flow. It uses a rubber tube, also known as a pinch tube and pinch mechanism to control the fluid. This valve is the simplest in any valve design.
Pinch tubes are manufactured of natural or synthetic rubbers and sometimes plastics which have good abrasion resistance properties. Most pinch valves are open style in which the pinch tube is exposed. However, another style fully encloses the pinch tube within a metallic body.
Pinch Valve – Application
It is ideally suited for the handling of slurries, liquids with large amounts of suspended solids, and systems that convey solid material pneumatically.
Pinch Valve –
Attention