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What is a cast-iron gate valve?

A Cast iron gate valve is a gate valve whose body and bonnet are made of cast iron material. Cast iron gate valves have been in use for hundreds of years. Cast iron gate valve has excellent resistance to temperature since it can withstand high temperatures of around 1150 oC. Cast iron gate valves also have high strength which makes them work at high pressure applications. However, the strength of the cast-iron gate valve will depend on the class of cast iron. Some cast-iron gate valves can withstand high pressures of around 500 psi. Cast iron gate valve as the name suggests, uses a gate to control fluid flow. Cast iron gate valves use the gate valve to either open or close fluid flow. These valves are bi-directional. The fluid flow and the gate in cast iron gate valves are perpendicular to each other. As such, the fluid flows in a straight line without taking direction in the cast iron gate valve which helps to reduce pressure loss. Cast iron gate valves have low fluid resistance as they are designed to enhance laminar flow (smooth flow/flow without turbulence). Cast iron gate valves are resistant to corrosion which makes them be used even in corrosive applications. These valves have high resistance to pressure and temperature. However, cast iron gate valves have a low resistance to impact damage since the material used to make them (cast iron) is of low ductility. 

Components of cast iron gate valve 

Valve body 

The valve body in a cast-iron gate valve is the main component as it houses all internal parts of the valve. The valve body is always made very strong so that it can help the valve withstand high pressure and high temperature. In cast iron gate valves, the valve body is made of cast iron. With cast iron being a strong material and resistant to high temperatures, it helps cast iron gate valves to withstand thermal distortion. 

Bonnet 

Bonnet is a component of a cast-iron gate valve that is placed on top of the valve body to cover the internal components of the cast-iron gate valve. The bonnet is also made of cast iron material just like the valve body. The bonnet is connected to the valve body using screws or bolts and nuts. The screw-bonnet enhances tight-seal which is free from leakage and is used in medium to high-pressure applications. The bolted-bonnet connection enhances tight-seal free from leakage and is used in high-pressure applications. The bolted-bonnet connection tends to make the cast iron gate valve heavy relative to the screwed bonnet connection because of the bolts and nuts used. 

Handwheel/actuator 

The handwheel is a component used in manual cast iron gate valves. When the cast-iron gate valve is not manual, it is driven by an actuator. The handwheel/actuator is used to provide torque to another component called a stem. The stem transmits the torque to the gate to open/close the fluid flow. The actuators that can be used in the cast iron gate valve include hydraulic, pneumatic, and electric actuators.  

Stem 

The stem is the component in a cast-iron gate valve that is connected to the actuator/handwheel to provide force for opening/closing the gate. The stem is also made of strong material like cast iron or another material like brass or bronze. Cast iron gate valve manufacturers design the stem such that as it moves it cause movement effect on the gate to make it either close or open the valve for fluid flow. 

Seat 

The seat in a cast-iron gate valve is an interior component that makes contact with the gate to make a leakage free tight seal. In cast iron gate valves, the seat comes in contact with the gate when the valve is shut. In a cast-iron gate valve, the seat is integral to the valve body or employs a seat ring configuration. The seat ring configuration is pressed or threaded into the valve body. The pressed seat is used in higher pressure applications. The seat in the cast iron gate valve can be made of different materials other than cast iron. However, this material should be able to withstand temperatures meant for that application. Some of the reliable materials used in cast Iron Gate valve to make the seat include bronze and brass as well as PTFE. However, the PTFE cannot be used in high-temperature applications as it may be distorted by thermal heat. 

Gate 

The gate is the component in the cast iron gate valve which is used to close/open the fluid flow. The gate in a cast-iron gate valve is connected to the stem so that when the handwheel is rotated it can move linearly upwards or downwards to open or close the fluid flow respectively. 

Trim 

Trim is a collective name given to internal components of the cast-iron gate valve. These components include stem, valve body surface, bushing, gate sealing surface among others. These components work together to enhance effective operation of a cast-iron gate valve. Failure of one component affects the efficiency and life of the whole cast iron gate valve can be affected adversely. 

Components of a cast iron gate valve

How does a cast-iron gate valve work? 

Cast iron gate valves work by using a gate to enhance fluid control through a pipeline. The gate in a cast-iron gate valve is connected to the stem. The stem is connected to the actuator/handwheel. When the actuator/handwheel is rotated it rotates the stem which transmits force to the gate. The force helps the gate to move linearly upwards or downwards to open or close the cast iron gate valve respectively. Cast iron gate valves are bi-direction and thus they can be used in any direction of choice. The rotation of the handwheel in the anticlockwise direction helps to open the valve while the direction of the handwheel in the clockwise direction helps to close the valve. The fluid flows through the gate in a cast-iron gate valve in a perpendicular direction which helps to reduce fluid resistance

Working of a cast iron gate valve

Rising stem and non-rising stem cast iron gate valves 

Rising stem cast iron gate valves are also known as outside screw and yoke (OS&Y). The OS&Y name is given because these valves have exposed screw that extends above the top of the bonnet. Rising stem cast iron gate valves are used in different applications among them water pump stations. The rising stem cast iron gate valves is advantageous in that it is very easy to tell when the valve is open or closed by looking at the screw or stem position. Non-rising stem cast iron gate valves are designed such that the stem can revolve in the bonnet. In this type of cast iron gate valve, the gate is lowered or raised by employing threads on the end of the stem. Cast iron gate valve manufacturers design non-rising stem valves with a gage or pointer to indicate when the valve is closed or open. 

Parallel disc cast iron gate valve 

These are cast iron gate valves that consist of two discs mounted apart against parallel seats using spring at the closure point. Parallel disc cast iron gate valve has one of the most famous valve known as cast iron knife gate valve with two parallel seats and a gate between the seats to enhance fluid shut-off. In some cases,

Parallel disc cast iron gate valve

solid-wedge cast Iron Gate valve 

A solid wedge cast iron gate valve is a valve mostly used in applications such as air services, gas, and oil. These valves use a wedge shape to enhance high additional seating load. Solid wedge cast iron gate valves can be installed in any direction suitable for the media being worked on. On certain occasions, it may be that the solid wedge cast iron gate valve cannot be opened till when the valve is reheated by system temperatures. Such a situation is known as thermal binding. 

 the parallel disc cast iron gate valves are limited to low-pressure drops and low-pressure applications. 

Solid-wedge cast Iron Gate valve

 

Types of cast iron gate valves 

Flexible wedge cast Iron Gate valve 

A flexible wedge cast iron gate valve is a valve that uses a single flexible wedge gate with a cut around it. The cut is of various depths, shapes, and sizes. The flexible wedge cast iron gate valve has no problem with thermal contraction and expansion as the gate is designed to compensate for thermal changes and thus make it easy to open. With such enhanced thermal capabilities, flexible wedge cast iron gate valves are used in steam systems to help prevent thermal blinding. 

Split wedge cast Iron Gate valve 

Split wedge cast iron gate valves are valves with two separate halves. Such design helps to allow an angular wedge between the outer faces to fit the valve seat enhancing self-adjustment and self-alignment to both seating surfaces. 

Slab cast iron gate valves 

Slab cast iron gate valves are unitary valves with bore-sized holes. When slab cast iron gate valves are opened, the hole coincides with two seat rings. With such a design, the valve controls the fluid flow with small turbulence. The slab cast iron gate valve helps to reduce pressure drop in the fluid flow system. Slab cast iron gate valve manufacturers design this valve with a plug. The plug is used to expel dirt that may accumulate in the gate valve cavity. These valves need to be kept clean thus the need for the plug. Slab cast iron gate valves are used in different applications among them to transport crude oil and natural gas liquids. 

 

Applications of cast iron gate valves 

  • Cast iron gate valves are used in steam power plants. 
  • Cast iron gate valves are used in salty fluid applications. 
  • Cast iron gate valves are used in transporting crude oil and natural gas liquids.
  • They are used in controlling flow of slurries. 
  • They are used in control of gas, steam, and liquids flow. 
  • Cast iron gate valves are used in chemical plants. 
  • Cast iron gate valves are used in high pressure and high-temperature applications. 
  • Cast iron gate valves are used in the food processing and beverages industries. 
  • They are used in pharmaceutical industries. 

 

Advantages of cast iron gate valves 

  • Cast iron gate valves have a low-pressure drop. 
  • Cast iron gate valves have low fluid resistance since the fluid flow is perpendicular to the valve gate. 
  • Cast iron gate valve can withstand high temperatures as high as 1150 oC.
  • These valves have high strength to withstand high pressure. 
  • Cast iron gate valves can be used as bi-directional valves. 
  • These valves are energy efficient because the fluid flow has very small turbulence as the fluid flows perpendicular to the valve gate. 
  • Cast iron gate valves have a simple body design which helps in repair, cleaning, and maintenance of the valve. 
  • Cast iron gate valves are used when fully open or fully closed which helps to reduce erosion on sealing surfaces. 

 

Disadvantages of cast iron gate valves 

  • Cast iron gate valves are susceptible to impact damage since their ductility is low. 
  • Cast iron gate valves are slow to open/close. 
  • Cast iron gate valves need a large area for their operation, maintenance, and installation. 
  • Cast iron gate valves are not meant for throttling applications. 

 

Troubleshooting cast Iron Gate valves 

Leakage in the valve seat

  • Clogged materials in the valve seat. Open the valve high enough to get a high velocity to flush the clogged dirt. Repeat the same process several times to ensure all dirt/debris is removed. 
  • This could also be due to a damaged seat. Check the seat seal and replace it if damaged. 

Leakage in the stem 

  • O-rings damaged. Replace the O-rings. 
  • Loose packing gland bolts. Tighten gland packing bolts. If it persists, replace the gland packing system. 

Leakage in the valve body 

  • The valve body may be cracked or damaged. This could be due to cast iron material used to make the valve body which is of low ductility and thus prone to impact damage. For damaged cast iron gate valve body, replace the body. 

Leakage in the connections 

  • Loose bolts and nuts. Tighten the bolts and nuts. 
  • Worn out gaskets. Replace the gaskets. 

The handle is not working

  • It could be due to foreign particles clogged. Clean the foreign materials. 
  • The handle could be damaged. Replace the handle as necessary. 

The cast-iron gate valve is not operating 

  • Broken stem. Replace the stem.
  • Gate and stem engagement are broken. Replace the product as necessary. 
  • Misaligned stem. Check the stem and align it.

 

Summary 

Cast iron gate valves are gate valves made of cast iron material. These valves have bonnet and the valve body made of cast iron material. The use of cast iron material to make cast iron gate valves is preferred because these material has high resistance to temperature. Cast iron gate valves are preferred because of their high strength which makes them withstand high pressure.

As the name suggests, cast iron gate valve manufacturers design these valves to block fluid flow with a gate. The gate is connected with the valve stem and then to the handwheel. When the handwheel is rotated, it makes the stem move upwards or downwards to open and close the fluid flow respectively. Cast iron gate valves are valves preferred not only for their high thermal and mechanical strength but also for their low-pressure drop. Cast iron gate valves have the gate perpendicular to the fluid flow which reduces pressure drop and fluid resistance. With low-pressure drop and low fluid resistance cast iron gate valves are energy efficient.

Cast iron gate valves are used in different applications such as HVAC, steam power plants, food and beverages processing, pharmaceuticals, water supply applications among others. Cast iron gate valves are of several types which include slab cast iron gate valve, wedge cast iron gate valve, rising stem cast iron gate valve, non-risings stem cast iron gate valve, parallel disc cast iron gate valve, solid-wedge cast iron gate valve, flexible wedge cast iron gate valve, and split wedge cast iron gate valve. The advantages of cast iron gate valves are low fluid resistance, low-pressure drop, and high resistance to fluid pressure, high thermal resistance, bi-directional fluid flow, energy-efficient, corrosion resistance, and minimal erosion. However, cast iron gate valves tend to get damaged easily by impacts because their ductility level is low. 

 

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What are valves

Valves are mechanical devices that controls the flow and pressure within a system or process. They are essential components of a piping system that conveys liquids, gases, vapors, slurries etc..

Different types of valves are available.. gate, globe, plug, ball, butterfly, check, diaphragm, pinch, pressure relief, control valves etc. Each of these types has a number of models, each with different features and functional capabilities. Some valves are self-operated while others manually or with an actuator or pneumatic or hydraulic is operated.

 

Functions from Valves are..

  • Stopping and starting flow
  • Reduce or increase a flow
  • Controlling the direction of flow
  • Regulating a flow or process pressure
  • Relieve a pipe system of a certain pressure

 

There are many valve designs, types and models, with a wide range of industrial applications. All satisfy one or more of the functions identified above. Valves are expensive items, and it is important that a correct valve is specified for the function, and must be constructed of the correct material for the process liquid.

Regardless of type, all valves have the following basic parts.. the body, bonnet, trim (internal elements), actuator, and packing. The basic parts of a valve are illustrated in the image on the right.

 

Valve Body

The valve body, sometimes called the shell, is the primary boundary of a pressure valve. He serves as the main element of a valve assembly because it is the framework that holds all the parts together.

The body, the first pressure boundary of a valve, resists fluid pressure loads from connecting piping. It receives inlet and outlet piping through threaded, bolted, or welded joints.

The valve-body ends are designed to connect the valve to the piping or equipment nozzle by different types of end connections, such as butt or socket welded, threaded or flanged.

Valve bodies are cast or forged in a variety of forms and each component have a specific function and constructed in a material suitable for that function.

 

Valve Body

Valve Bonnet

Valve body

Valve Bonnet

The cover for the opening in the body is the bonnet, and it is the second most important boundary of a pressure valve. Like valve bodies, bonnets are in many designs and models available.

A bonnet acts as a cover on the valve body, is cast or forged of the same material as the body. It is commonly connected to the body by a threaded, bolted, or welded joint. During manufacture of the valve, the internal components, such as stem, disk etc., are put into the body and then the bonnet is attached to hold all parts together inside.

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, represent a significant cost portion of valve cost, and are a source for potential leakage.

 

Valve Trim

The removable and replaceable valve internal parts that come in contact with the flow medium are collectively termed as Valve trim. These parts include valve seat(s), disc, glands, spacers, guides, bushings, and internal springs. The valve body, bonnet, packing, et cetera that also come in contact with the flow medium are not considered valve trim.

A Valve’s trim 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.

 

Valve trim parts may be constructed of assorted materials because of the different properties needed to withstand different forces and conditions. Bushings and packing glands do not experience the same forces and conditions as do the valve disc and seat(s).

Flow-medium properties, chemical composition, pressure, temperature, flow rate, velocity and viscosity are some of the important considerations in selecting suitable trim materials. Trim materials may or may not be the same material as the valve body or bonnet.

 

API 600 Valve’s Trim No

Valve Disk and Seat(s)

Valve Disk and Seat(s)

Disc The disc is the part which allows, throttles, or stops flow, depending on its position. In the case of a plug or a ball valve, the disc is called plug or a ball. The disk is the third most important primary pressure boundary. With the valve closed, full system pressure is applied across the disk, and for this reason, the disk is a pressure related component. Disks are usually forged, and in some designs, hard surfaced to provide good wear properties. Most valves are named, the design of their disks.

 

Seat(s) The seat or seal rings provide the seating surface for the disk. A valve may have one or more seats. In the case of a globe or a swing-check valve, there is usually one seat, which forms a seal with the disc to stop the flow. In the case of a gate valve, there are two seats; one on the upstream side and the other on the downstream side. A gate valve disc has two seating surfaces that come in contact with the valve seats to form a seal for stopping the flow. To improve the wear-resistance of the seal rings, the surface is often hard-faced by welding and then machining the contact surface of the seal ring. A fine surface finish of the seating area is necessary for good sealing when the valve is closed. Seal rings are not usually considered pressure boundary parts because the body has sufficient wall thickness to withstand design pressure without relying upon the thickness of the seal rings.

 

Valve Stem

The valve stem provides the necessary movement to the disc, plug or the ball for opening or closing the valve, and is responsible for the proper positioning of the disk. It is connected to the valve handwheel, actuator, or the lever at one end and on the other side to the valve disc. In gate or globe valves, linear motion of the disc is needed to open or close the valve, while in plug, ball and Butterfly valves, the disc is rotated to open or close the valve.

Stems are usually forged, and connected to the disk by threaded or other techniques. To prevent leakage, in the area of the seal, a fine surface finish of the stem is necessary.

There are five types of valve stems..

  • Rising Stem with Outside Screw and Yoke
    The exterior of the stem is threaded, while the portion of the stem in the valve is smooth. The stem threads are isolated from the flow medium by the stem packing. Two different styles of these designs are available; one with the handwheel attached to the stem, so they can rise together, and the other with a threaded sleeve that causes the stem to rise through the handwheel. This type of valve is indicated by “O. S. and Y.” is a common design for NPS 2 and larger valves.
  • Rising Stem with Inside Screw
    The threaded part of the stem is inside the valve body, and the stem packing along the smooth section that is exposed to the atmosphere outside. In this case, the stem threads are in contact with the flow medium. When rotated, the stem and the handwheel to rise together to open the valve.
  • Non Rising Stem with Inside Screw
    The threaded part of the stem is inside the valve and does not rise. The valve disc travels along the stem, like a nut if the stem is rotated. Stem threads are exposed to the flow medium, and as such, are subjected to the impact. That is why this model is used when space is limited to allow linear movement, and the flow medium does not cause erosion, corrosion or abrasion of the stem material.
  • Sliding Stem
    This valve stem does not rotate or turn. It slides in and out the valve to open or close the valve. This design is used in hand-operated lever rapid opening valves. It is also used in control valves are operated by hydraulic or pneumatic cylinders.
  • Rotary Stem
    This is a commonly used model in ball, plug, and Butterfly valves. A quarter-turn motion of the stem open or close the valve.

In the main Menu “Valves” you will find some links to detailed (large) images of Rising and NON Rising Stem valves.

 

Valve Stem Packing

For a reliable seal between the stem and the bonnet, a gasket is needed. This is called a Packing, and it is fitted with e.g. the following components..

  • Gland follower, a sleeve which compresses the packing, by a gland into the so called stuffing box.
  • Gland, a kind of bushing, which compressed de packing into the stuffing box.
  • Stuffing box, a chamber in which the packing is compressed.
  • Packing, available in several materials, like Teflon®, elastomeric material, fibrous material etc..
  • A backseat is a seating arrangement inside the bonnet. It provides a seal between the stem and bonnet and prevents system pressure from building against the valve pakking, when the valve is fully open. Back seats are often applied in gate and globe valves.

An important aspect of the life time of a valve is the sealing assembly. Almost all valves, like standard Ball, Globe, Gate, Plug and Butterfly valves have their sealing assembly based upon shear force, friction and tearing.

Therefore valve packaging must be properly happen, to prevent damage to the stem and fluid or gas loss. When a packing is too loose, the valve will leak. If the packing is too tight, it will affect the movement and possible damage to the stem.

 

Typical sealing assembly

 

1 Gland Follover 2 Gland 3 Stuffing Box with Packing 4 Back Seat

Typical sealing assembly

 

Valve Yoke and Yoke Nut

Yoke

A Yoke connects the valve body or bonnet with the actuating mechanism. The top of the Yoke holding a Yoke nut, stem nut, or Yoke bushing and the valve stem passes through it. A Yoke usually has openings to allow access to the stuffing box, actuator links, etc.. Structurally, a Yoke must be strong enough to withstand forces, moments, and torque developed by the actuator.

Yoke Nut

A Yoke nut is an internally threaded nut and is placed in the top of a Yoke by which the stem passes. In a Gate valve e.g., the Yoke nut is turned and the stem travels up or down. In the case of Globe valves, the nut is fixed and the stem is rotated through it.

 

Valve Actuator

Hand-operated valves are usually equipped with a handwheel attached to the valve’s stem or Yoke nut which is rotated clockwise or counter clockwise to close or open a valve. Globe and gate valves are opened and closed in this way.

Hand-operated, quarter turn valves, such as Ball, Plug or Butterfly, has a lever for actuate the valve.

 

There are applications where it is not possible or desirable, to actuate the valve manually by handwheel or lever. These applications include..

  • Large valves that must be operated against high hydrostatic pressure
  • Valves they must be operated from a remote location
  • When the time for opening, closing, throttle or manually controlling the valve is longer, than required by system-design criteria

These valves are usually equipped with an actuator.
An actuator in the broadest definition is a device that produces linear and rotary motion of a source of power under the action of a source of control.

Basic actuators are used to fully open or fully close a valve. Actuators for controlling or regulating valves are given a positioning signal to move to any intermediate position. There a many different types of actuators, but the following are some of the commonly used valve actuators..

  • Gear Actuators
  • Electric Motor Actuators
  • Pneumatic Actuators
  • Hydraulic Actuators
  • Solenoid Actuators

For more information about Actuators see main Menu ‘Valves’

 

Classification of Valves

The following are some of the commonly used valve classifications, based on mechanical motion..

  • Linear Motion Valves. The valves in which the closure member, as in gate, globe, diaphragm, pinch, and lift Check Valves, moves in a straight line to allow, stop, or throttle the flow.
  • Rotary Motion Valves. When the valve-closure member travels along an angular or circular path, as in butterfly, ball, plug, eccentric- and Swing Check Valves, the valves are called rotary motion valves.
  • Quarter Turn Valves. Some rotary motion valves require approximately a quarter turn, 0 through 90°, motion of the stem to go to fully open from a fully closed position or vice versa.

 

Classification of Valves based on Motion

Valve Types Linear Motion Rotary Motion Quarter Turn
Gate YES NO NO
Globe YES NO NO
Plug NO YES YES
Ball NO YES YES
Butterfly NO YES YES
Swing Check NO YES NO
Diaphragm YES NO NO
Pinch YES NO NO
Safety YES NO NO
Relief YES NO NO

 

Class Ratings

Pressure-temperature ratings of valves are designated by class numbers. ASME B16.34, Valves-Flanged, Threaded, and Welding End is one of the most widely used valve standards. It defines three types of classes.. standard, special, and limited. ASME B16.34 covers Class 150, 300, 400, 600, 900, 1500, 2500, and 4500 valves.

 

Summary

On this page are defined a number of basic information from valves.

As you may have seen in the main Menu “Valves”, you can find also information about several and often applied valves in Petro and chemical industry.
It can give you an impression, and good understanding of the differences between the various types of valves, and how these differences affect the valve function. It will help to a proper application of each type of valve during the design and the proper use of each type of valve during operation.

 

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Valve maintenance and installation operation

The installation and use of the valve are closely related to the maintenance of the valve, which needs careful operation. Even small mistakes should be avoided. The long-term use of the valve without defects can improve the project quality. For small valves, how to maintain them to meet people’s maximum expectations? In order to better familiarize those who need to know this direction, I will summarize and explain here.

1, before installing the valve, carefully check the logo and the instructions of the certificate of conformity on it to ensure correct installation. In addition, clean the inside of the valve before this to avoid magazine gambling on the nozzle.

2, as the key button of the switch, the valve can be installed in all required places on the pipeline. If the transmission device is connected, it shall be installed vertically, which is conducive to the operation and inspection of valve maintenance

3, the valve shall be installed in accordance with the direction of medium flow. Make the flow direction of the medium consistent with the arrow direction marked by the valve body.

 

4, the connecting parts between the valve and the pipeline shall be tightened according to the diagonal direction for many times, and shall not be tightened at one time, which is easy to cause uneven stress and leakage at the connection.

5, the sealing bite is appropriate. It is not suitable to be too tight or too loose. Keep the balance to prevent sundries from entering the inside of the valve and scratching the sealing surface. If pressure test is required, the pressure at both ends shall be consistent.

6, when opening the valve, turn the hand wheel clockwise. When closing, turn the hand wheel counterclockwise. Rotate the valve in place according to the opening and closing instructions.

Finally, there are many kinds of valves. Although they can’t be listed here, they all have instructions for reference. The maintenance of each valve is different, and it is not easy to copy. Before starting the operation, master the method first, and then implement it.

Gate Valve Installation & Maintenance Instructions

Gate Valves of all materials and seat types are easy to use and long lasting when they are installed and maintained correctly. The installation technique varies slightly for different end connections (eg. flanged vs rolled groove vs victaulic) but the other instructions remain the same.

Storage Conditions

  • To protect the seat and seals do not unpack the valves until they are ready for installation. By doing this you are protecting the valve from dust and debris which may eventually cause seat leakage.
  • Keep in a cool well ventilated space if storing for a longer period of time.
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butterfly valves

Introduction

This article takes a detailed look at butterfly valves.

Read further and learn more about:

  • What is a butterfly valves.?
  • How does it work?
  • Components of a butterfly valves.
  • Types of butterfly valves.
  • Materials for the construction of butterfly valves.
  • Advantages and disadvantages of butterfly valves.
  • And much more…
  •                                             

 

 

 

 

 

 

 

Chapter 1: What is a Butterfly Valve?

A butterfly valve is a quarter-turn rotational motion device that utilizes a rotary disc to allow, obstruct, or control the flow of fluids in a piping system. It features a rotating disc that is situated on the passageway of the flowing media. The disc is rotated and controlled by an external actuating mechanism through the stem attached to it. When the disc is coplanar to the flow cross-sectional area, the flow is fully obstructed. Otherwise, the fluid is fully or partially allowed to pass through the butterfly valve. It takes a 900 turn to fully open a butterfly valve from a closed position, which means the disc should lie perpendicular to the flow cross-sectional area.

Butterfly valves are quarter-turn valves like ball valves and plug valves. They have a fairly simple construction and operation mechanism, and they have a compact size designed to fit two pipe flanges.

They can be operated manually or by an automatic actuating mechanism that is integrated into the process control system of the pipeline. They are ideal for on-and-off applications, but their applications to flow throttling are limited.

There are several types and designs of butterfly valves available, rated in varying temperatures, pressures, and flow rates to suit the needs of pipeline systems handling liquids and gases.

Chapter 2: Components of a Butterfly Valve

The main components of a butterfly valve are the following:

Valve Body

Made from a tough and rigid material, the valve body houses and protects the disc and other internal components of the butterfly valve. It links the valve to the piping system and to the external operating mechanism that controls the disc.

Disc

The disc is the main feature of butterfly valves that permits, regulates, and stops the flow of the fluid in the pipeline. Flow is controlled by the rotary motion of the disc. The discharge flow rate depends on the degree of disc opening. When the disc is perpendicular to the flow‘s cross-sectional area, the fluid is fully obstructed from flowing out of the valve. Otherwise, the fluid is permitted to flow through the space between the seat and the disc. It takes a 900-rotation from a closed position of the disc to allow full opening of the valve and vice versa. Flow is throttled when the disc is rotated less than 900.

The butterfly valve disc is analogous to the ball for ball valves and the plug for plug valves.

Stem

The stem is a shaft that connects the disc to the external operating mechanism. It is sealed by O-rings and bushings to prevent fluid leakage. The stem can be made from a one-piece shaft or two-piece (split-stem) shaft. The placement of the stem axis and its connection to the disc depends on the type of butterfly valve.

Seat

The valve seat is a ring that provides sealing between the disc edge and the valve body when it is in a closed position. The sealing action is necessary to avoid leakage of any fluid to the discharge of the butterfly valve. Since the disc slides on the surface of the seat during valve opening, it must be made from a material with a low coefficient of friction.

The butterfly valve seat can be made a soft seat or a metal seat. The material of the seat limits the temperature and pressure rating of the butterfly valve. Soft seats, which are made from plastic and elastomeric materials, are limited to lower temperatures because they deform at elevated temperatures.

Operating Mechanism

The external operating mechanism of a butterfly valve controls the fluid flow across the valve. It may be operated by manual rotation of the stem or by automatic actuation.

Manual operation of butterfly valves involves the application of torque to the lever or handwheel attached to the stem. Levers can set the valve into a closed, fully-opened, or partially-opened position. Larger butterfly valves are equipped with handwheels and gearboxes to increase torque and to aid in the opening and closing of the valve.

Automatic actuation may be used to control the butterfly valve situated in harsh environments and remote locations. It makes the opening and closing of butterfly valves faster, especially for larger valves requiring larger amounts of torque. The types of actuations used in butterfly valves to turn the valve stem are electromechanical actuation, (which uses an electric-powered motor), pneumatic actuation (which moves a piston or a diaphragm with compressed air), and hydraulic actuation, (which moves a piston or a diaphragm with hydraulic pressure).

Chapter 3: Types of Butterfly Valves

There are three main types of butterfly valves:

Zero Offset Butterfly Valves (Resilient Seat Butterfly Valves)

In zero offset butterfly valves, the stem passes through the centerline of the disc that is centered in the seat; all of this is centered inside the valve body. The valve body, seat, and disc lie concentrically when it is in a closed position. The disc rotates on the central axis; this allows a 3600 rotation. In a fully-opened position, the flow is divided into two halves on each side of the disc, which is now parallel to the flow. The advantage of this type is that the flowing media does not come in contact with the valve body because the seat is covering it.

Zero offset butterfly valves have resilient soft seats because they depend on the flexibility and deformation of the soft seat during sealing. This causes the disc edges to slide onto the seat, which results in full friction between them during the operation. This reduces the service life of the valve. Since the design requires the seat to be made from a polymeric or elastomeric material, it is limited to lower pressure and temperature ratings.

Zero offset butterfly valves are used in liquid and gas pipelines, which have pressure and temperature ratings of 250 psi and 4000F, respectively.

Double Offset Butterfly Valve (High-Performance Butterfly Valves)

In double offset butterfly valves, the stem axis is offset behind the centerline of the seat and the body (first offset), then the stem axis is further offset from the vertical centerline of the valve (second offset). When the disc is opened, the seat is lifted from the seal; this reduces the friction during the first and last 10 degrees of the valve opening and closing, respectively. This results in a smoother valve operation, better sealing capability, and longer service life than the zero offset butterfly valve.

Like zero offset butterfly valves, double offset butterfly valves use a soft seat. They are available in moderate pressure and temperatures ratings, which are capable of withstanding higher pressures and temperatures than the zero offset butterfly valves in liquid and gas pipelines.

Double offset butterfly valves are typically used in water purification, wastewater treatment, HVAC, and fire protection systems (e.g., fire sprinklers). For increased temperature resistance, the amount of soft seat material is reduced by backing it with a layer of metal.

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Ball Valve Basics

Welcome to the first in a series of Valve Basics articles, each focused on a major product type and written especially for newcomers to the industries that use and make valves and related products.

Ball valves may not bounce very well but they work great at regulating flow. The popular valve is named for its round ball that sits in the interior of the valve body and pushes into a seat to control or provide on/off functions in fluid pipelines.

API 6D trunnion ball valves.

API 6D trunnion ball valves.

The heritage of ball valves is much shorter compared to gate, globe and check valve designs. Although the first ball valve patent was issued in 1871, it would take another 85 years for ball valves to become a commercial success. The discovery of polytetrafluoroethylene (PTFE, or “Teflon”) during the process design for manufacturing the atomic bomb in World War II, would be the catalyst that started the ball valve industry rolling. Ball valves come in all materials from brass to carbon steel and stainless steel to zirconium.

There are two basic types: floating ball and trunnion ball. These two designs allow for the construction of effective ball valves from ¼” through 60” and larger. Generally, the floating design is used for smaller and lower-pressure valves, while the trunnion type is used for larger and higher-pressure valve applications.

Floating ball valve.

Floating ball valve.

The reason for the two types of ball valves has to do with the way they seal and how the fluid force is distributed from the line flow to the ball and then to the seat. In the floating ball design, the ball is riding snugly between two seats, one upstream and one downstream. The force of the fluid acts on the ball to push it into the seat located in the downstream valve body. Since the ball covers the entire flow bore, all the force in the stream is pushing against the ball to force it into the seat. If the ball gets to be too large and the pressure too high, the force will be so great on the seat that the valve cannot be operated because the operating torque would be too high.

Floating ball valves come in a variety of body styles, although the two-piece, end entry type is the most popular. Other body styles include three-piece and top entry. Floating ball valves are manufactured in sizes up to 24” and class 300, but the practical realm of the floating ball valve is generally much lower—up to about 12”.

Although ball valves are designed primarily to be on/off or “block” valves, the addition of partial ball and V-port ball designs can make them good choices for control-type applications.

RESILIENT SEATS

The smaller floating ball valves are found in many different applications from household plumbing to those containing the harshest chemicals. The most popular seating material in these valves is some form of thermoplastic, such as PTFE. PTFE seats work very well because they are soft enough to seal well on to the polished metallic ball, yet firm enough not to blow out of the valve. The two primary concerns with these soft-seated valves are that they are susceptible to scratching (and potential leakage) and are limited to temperatures below the melting point of the thermoplastic seats—somewhere around 450oF (232oC) depending on the exact seat material.

A ball valve

A ball valve “ball.”

A feature of many resilient-seated floating ball valves is the ability to moderately seal in the event of a fire that causes the primary seats to melt. This is called a fire-safe design; it features a seat pocket that not only holds the resilient seat in place, but also provides a metallic seating surface that can provide a partial seal as it contacts the ball. The fire-safe design is confirmed by testing the valve in accordance with the American Petroleum Institute (API) 607 or 6FA fire-testing standards.

TRUNNION DESIGN

When larger sizes and higher-pressure ball valves are needed, the design shifts to the trunnion style. The trunnion differs from the floating style in that the trunnion ball is held in the body via a trunnion (short, attached stem) in the bottom and by the stem at the top. Since the ball cannot “float” into the seat to attain positive closure, the seat must float to the ball instead. The trunnion seat is designed so that the seat is energized by the upstream pressure and is forced into the ball to seal. Because the ball is held securely in place, except for its 90o rotation, the extraordinary fluid force and pressure does not jam the ball into the seat. Instead, the force acts only on a small area on the periphery of the floating seat.

The trunnion ball valve is the brawny big brother to the floating ball valve and as such it gets to handle the big jobs—high pressures and large pipe diameters. By far the most popular use of trunnion ball valves is for pipeline service. These valves are especially popular in natural gas pipelines in diameters up to 60” and pressures up to class 600. Trunnion ball valves can also be used in higher pressures if required. By using trunnion designs the torque required to open and close the valve is lower, so smaller actuators can be used.

End-entry design.

End-entry design.

The trunnion design also lends itself well to double block and bleed service since both the upstream and downstream seats float independently and most designs also feature a body or drain connection. Trunnion designs often employ seat lubrication ports where a lubricant can be injected around the seat to assist in closure efficacy.

METAL-SEATED DESIGNS

The biggest advancement in ball valve technology over the past 30 years or so is the metal-seated ball valve. While the idea of metal seats and a metal ball are not new—in fact, the first ball patent in 1871 featured a brass ball and brass seats—the design needed advancements in coating technology to really be perfected.

The metal-seated ball valve design has enabled ball valves to take a big chunk out of the market share dominated for decades by the venerable gate valve. The metal-seated, specialty-coated ball closes tightly against a set of precision coated and lapped seats, providing zero-leakage, if the hardened seating surfaces are not scratched by debris in the line.

BALL VALVE STANDARDS

The are several standards that apply to ball valves. The following table lists the most common ball valve design documents:

Ball valves have made huge inroads in replacing other valve types over the past 40 years. The cost to manufacture the smaller sizes has dropped greatly as well, making them even more competitive. The advances in coatings and metal-seated ball valve technology have created very robust designs that have resulted in an attractive total cost of ownership.

Table 1. Common ball valve standards.

Table 1. Common ball valve standards.

While the overall industrial valve segment is still dominated by gate and globe, linear-valve designs, the relatively young ball valve is steadily making up ground, and the metal-seated types have become the preferred valve design for severe-service applications around the world.

In need of assistance in selecting a ball valve ? The experts at STV VAlVE have the knowledge and experience to help. Shop stvvalve.com today!

What-is-a-Gate-Valve-and-How-does-they-work

Gate Valve – How They Work


Figure 1: Gate valve

A gate valve controls the medias flow by lifting the gate (open) and lowering the gate (closed). A gate valves distinct feature is the straight-through unobstructed passageway, which induces minimal pressure loss over the valve. The unobstructed bore of a gate valve also allows for a pigs passage in cleaning pipe procedures, unlike butterfly valves. Gate valves are available in many options, including various sizes, materials, temperature and pressure ratings, and gate and bonnet designs.

Gate valves tend to be slightly cheaper than ball valves of the same size and quality. They are slower in actuation than quarter-turn valves and are for applications where valve operation is infrequent, such as isolating valves. Gate valves should be used either fully open or fully closed, not to regulate flow. Automated gate valves exist with either an electric or pneumatic actuator, but a manual gate valve is cost-effective since they have infrequent usage.

Table of Contents

Functioning principle

Gate Valve ComponentsFigure 2: Gate valve components

A gate valves main components as seen in figure 2 are the handwheel (A), spindle (B), gasket (C), bonnet (D), valve body (E), flange (F), and gate (G). The primary operation mechanism is straightforward. Turning the handwheel rotates the stem, which moves the gate up or down via the threads. They require more than one 360° turn to fully open/close the valve. Lifting the gate from the path of the flow, the valve opens. Lowering the gate to its closed position seals the bore resulting in a full closure of the valve.

For a gate valve, the relationship between the gates vertical travel and the flow rate is nonlinear, with the highest changes occurring near shutoff. When used to regulate flow, the relatively high velocity of the flow at partial opening results in gate and seat wear, which along with possible vibrations of the gate, shortens the valves service life.

Gate valve design & types

Gate valves come in a wide variety of designs, each of which uses different technologies to meet various application requirements.

Bonnets

Bolted bonnet gate valveFigure 3: Bolted bonnet gate valve

A bonnet protects the internal parts of a gate valve (Figure 2). It is screwed in or bolted to the valve body, creating a leak-proof seal. Therefore, it is removable for repair or maintenance purposes. Depending on applications, gate valves can have screw-in, union, bolted, or pressure seal bonnets.

Screw-in Bonnets

Screw-in bonnets are the simplest in construction. They are common in small size valves and provide a durable leak-proof seal.

Union Bonnets

Union bonnets are held in place by a union nut. The union nut sits on the lower edge of the bonnet and screws into the valve bodys threads. This type of design ensures that the leak-proof seal created by the nut does not deteriorate by frequent removal of the bonnet. Therefore, union bonnets are common for applications that require regular inspection or maintenance.

Bolted Bonnets

Bolted bonnets provide sealing in larger valves and higher pressure applications. In this type, the bonnet and valve body are flanged and bolted together. Figure 3 shows a gate valve with a bolted bonnet.

Pressure Seal Bonnets

Pressure seal gate valves are ideal for high-pressure applications (more than 15 MPa). This type of construction uses internal pressure to create a better seal. Pressure seal bonnets have a downward-facing cup inserted into the valve body. When internal fluid pressure increases, the cups forced outward, improving the seal.

Gates

The gate comes in a variety of designs and technologies to produce effective sealing for differing applications.

Wedge Gates

In most gate valves, the gate has a wedge form and sits on two inclined seats (Figure 4). In addition to the primary force created by fluid pressure, a high wedging force on the seats created by the stems tightening assists with the sealing. The wedge-shaped gate does not stick to the seat in case of high fluid differential pressure and has an increased service life due to less “rubbing” on the seats.

Wedge gate valve vs parallel gate valveFigure 4: Wedge gate valve vs parallel gate valve

Parallel Slide Gates

Gate valves can also come in a parallel form where the gate is flat, and the seats are parallel. Parallel gate valves use line pressure and positioning to make a tight seal. Flat gates consist of two pieces and have a spring in the middle. The spring pushes the pieces towards the seats for enhanced sealing. Due to their inherent design, parallel gate valves have a safety advantage in higher temperature applications. In wedge-shaped gate valves, an additional compression load on the seats may result in thermal binding and restricted opening of the valve due to expansion. Furthermore, since there is no wedging action in parallel gates, closing torques are comparatively smaller, resulting in smaller, less expensive actuators or less manual effort. Due to their sliding into position, parallel gates keep dirt away from the seating surfaces.

Slab Gates

Slab Gate ValveFigure 5: Slab gate valve

Slab gates, also called through-conduit gate valves, are one-unit gates that include a bore size hole (Figure 5). In the open state, the bore is in line with the two seat rings. This alignment creates a smooth flow with minimal turbulence. This unique design allows for minimal pressure loss on the system and is perfect for the transportation of crude oil and natural gas liquids (NGLs). The valve seats remain clean. However, the disc cavity can capture foreign material. Therefore, the cavity typically has a built-in plug for maintenance purposes of draining the accumulated foreign material.

Parallel Expanding Gates

Expanding gate valves have two slab gates matched together that provide sealing through the mechanical expansion of the gate (Figure 6). When lifted, both of the slab gates cavity allows the media to flow. The upward force on one slab and the stoppage of the second slab, by a step in the valve body, allows for outward mechanical expansion for a proper seal. When closed, the slab gates block the media flow, and the downward force (stem) on one slab and upward force (step in valve body) allows for outward mechanical expansion for a proper seal.

These valves provide an effective seal simultaneously for both upstream and downstream seats. This seal makes them ideal for applications like isolation valves in power plants, block valves in process systems, and high-temperature valves in refineries.

Expanding gate functioningFigure 6: Expanding gate functioning

Knife Gates

Knife gate valves are for thick fluids and dry bulk solids. The gate is only one piece of metal, which is typically pointed. These valves are self-cleaning as they pass the seat rings every time they open and close.

Stem design

The gate is raised and lowered by the spinning of a threaded stem. A manual wheel or actuator spins the stem. Depending on the design, the stem is either considered rising or non-rising. So, as you spin the stem it either raises or stays in place with the spin as seen in Figure 7.

Outside Screw and Yoke (OS&Y), also referred to as rising stems, are fixed to the gate. Therefore, the threads are on the actuation side. So, as the gates raised or lowered, the stem moves with it up and down. Consequently, they have built-in visual indicators of the state of the valve and are easily lubricated. Since they have moving components, they cannot be used with bevel gears or actuators. Therefore, rising gate valves are suitable for manual actuation.

On the other hand, a non-rising stem is fixed to the actuator and threaded into the gate. An indicator is often threaded onto the stem to show the open or closed state of the valve. Non-rising gate valves are common in underground installations and applications with limited vertical space.

Mechanism of rising stem gate valves vs non-rising stem gate valvesFigure 7: Mechanism of rising stem gate valves vs non-rising stem gate valves

FAQ

What is a gate valve?

A gate valve controls the medias flow by lifting the gate (open) and lowering the gate (closed).

How does a gate valve work?

By rotating the manual handle, the threaded stem moves the gate up and down. As the gate goes up it opens and down it closes the media flow.

What is a gate valve used for?

A gate valve is for on and off flow control.

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What is a Y Strainer and How to Work

A Y strainer, sometimes referred to as a y strainer, is designed to mechanically remove solids and other particles from fluids. They are an essential component in numerous fluid control applications to ensure no down-stream component is affected by particles within the fluid. In this article we will review their design, use cases, how to size the mesh filter, materials, and how to clean them.

Table of Contents

Y Strainer Design

As its name implies, a Y strainer is shaped like a “Y” and is used to filter, or strain, out particulates from steam, gas or liquid. This mechanical straining process is made possible via a filter element comprised of mesh, perforated metal, or a wedge wire straining element. The most common kind of straining element is a wire mesh. Some also include “blow-off valves” that make the cleaning process easier in applications with more substantial dirt blowing. The strainer itself has a compact, Y shaped design. The Y shape has better flow characteristics then for example a T shaped strainer, because the fluid flows through the filter with less change of direction.

Why Use a Y Strainer?

In general, Y strainers are critical anywhere clean fluids are required. While clean fluids can help maximize the reliability and lifespan of any mechanical system, theyre especially important with solenoid valves. This is because solenoid valves are very sensitive to dirt and will only function properly with clean liquids or air. If any solids enter the stream, it can disrupt and even damage the entire system. Therefore, a Y strainer is a great complimentary component. In addition to protecting the performance of solenoid valves, they also help safeguard other types of mechanical equipment, including:

  • Pumps
  • Turbines
  • Spray nozzles
  • Heat exchangers
  • Condensers
  • Steam traps
  • Meters

A simple Y strainer can keep these components, which are some of the most valuable and expensive parts of the pipeline, protected from the presences of pipe scale, rust, sediment or any other kind of extraneous debris. Y strainers are available in a myriad of designs (and connection types) that can accommodate any industry or application.

Sizing Your Mesh Filter for a Y strainer

Of course, the Y strainer wouldnt be able to do its job without the mesh filter that is properly sized. To find the strainer thats perfect for your project or job, it’s important to understand the basics of mesh and screen sizing. There are two terms used to describe the size of the openings in the strainer through which debris passes. One is micron and the other is mesh size. Though these are two different measurements, they describe the same thing.

What is a Micron?

Standing for micrometer, a micron is a unit of length thats used to measure tiny particles. For scale, a micrometer is one thousandth of a millimeter or about one 25-thousandths of an inch.

What is Mesh Size?

A strainers mesh size indicates how many openings there are in the mesh across one linear inch. Screens are labeled by this size, so a 14-mesh screen means youll find 14 openings across one inch. So, a 140-mesh screen means that there are 140 openings per inch. The more openings per inch, the smaller the particles that can pass through. The ratings can range from a size 3 mesh screen with 6,730 microns to a size 400 mesh screen with 37 microns.

Micron-to-Mesh Conversion Chart

The chart below is a handy resource to help you convert from mesh to micron (or vice-versa).

 

 

Mesh Screen Mesh Size Microns
2000 10 0.0787
1680 12 0.0661
1410 14 0.0555
1190 16 0.0469
1000 18 0.0394
841 20 0.0331
707 25 0.028
595 30 0.0232
500 35 0.0197
420 40 0.0165
354 45 0.0138
297 50 0.0117
250 60 0.0098
210 70 0.0083
177 80 0.007
149 100 0.0059
125 120 0.0049
105 140 0.0041
88 170 0.0035
74 200 0.0029
63 230 0.0024
53 270 0.0021
44 325 0.0017
37 400 0.0015

In addition, it can be helpful to see an example of mesh sizes based on certain particles, as shown below:

 

 

Mesh Size Microns Example of particle size
14 0.05551400
28 0.028700 Beach Sand
60 0.0098250 Fine Sand
100 0.0059150
200 0.002974 Portland Cement
325 0.001744 Silt
400 0.001537 Plant Pollen

Determining Your Proper Filter Size

To select the right filter size for your application, youll need to consider the size, scope, and environment of the project. Some of the most important factors to gauge include:

  • The type of pipe system youre using.
  • The kind of material that makes up the system.
  • The size of the debris or particles you want to capture.
  • The systems pressure and temperature levels.

Its important to take the time to size your mesh filter correctly. Sizing it too small or too large can negatively affect your system as a whole. If your filter is too small (with a lot of openings), there will be a greater pressure drop from inlet to outlet. Additionally, removing too much debris can result in additional maintenance due to a collection of debris which can also cause an increased pressure drop. If it is too large (allowing large particles through), this can affect the performance and life span of your downstream equipment.

Housing Material Options

Now that weve covered why Y strainers are important and what theyre used for, lets discuss a few of the different kinds of Y strainers available. These strainers are available in a wide variety of material types and fall into different classes defined by the American National Standards Institute (ANSI). First, lets take a look at the different material housing options available, which include:

  • Brass
  • Stainless steel
  • (Carbon) Steel
  • Bronze
  • Cast iron
  • Ductile iron
  • Plastics

Note that these different kinds of housing materials are designed to fit certain environments and media.

Seal Material Options

The seal on a Y strainer helps ensure its functionality and extend its service life. Some of the common options are:

PTFE Seal

This is one of the most common types of seal materials. In addition to holding fast in even the most aggressive environments, these are also ideal for low and high temperatures.

Fluoro Rubber Seal

When youre shopping for a Y strainer, you might come across a few different kinds of seals that sound similar. These include:

  • FKM
  • FPM
  • Viton®

These individual designations all describe the same base material: Fluoro rubber. Why the different names? In short, the ASTM abbreviates the material as FKM while the DIN/ISO abbreviates the entire fluoroelastomer category as FPM. And, DuPont Performance Elastomers trademarked the material as Viton®.

EPDM Seal

Standing for ethylene-propylene-diene-monomer, EPDM is an elastomer similar to Fluoro rubber. However, it features a different chemical resistance and temperature range compared to FPM.

How to Clean Your Y Strainer

How often youll need to clean your component depends on the process youre running, mesh size, and the materials youre filtering. Remember to close off all valve connections on both sides of the Y strainer to relieve pressure as you start to clean. From there, you can loosen and remove the plug at the end of the filter leg to access the filter. Empty out all of the collected material and debris, clean the filter and replace.

Y Strainer Selection Criteria

There are different kinds of Y strainers on the market designed to meet various industry needs. As you research which one is best for you, keep the following criteria in mind:

  • Port size
  • The temperature in your environment
  • The pressure level in your environment
  • Preferred installation orientation
  • The kind of debris you need to strain
  • Ease of maintenance

There is no one-size-fits-all Y strainer that meets every need. Thats why its important to understand your application requirements before moving forward.

Typical Y Strainer Applications

A Y strainer is most valuable in an environment that requires constant protection from debris and contamination. Lets take a look at a few of the most common applications that require their use.

Steam Applications

These strainers are a go-to resource in most steam applications, as its shape is built to handle the high pressure that exists in these environments.

Liquid Applications

Liquid applications tend to become infiltrated by sand and gravel, and Y strainers can help keep those particles out to ensure the liquid stays clean. Especially when they work in tandem with other water-handling applications, these strainers can protect important (and expensive) equipment from damage, corrosion or clogs that could result from such contamination.

Natural Gas and Air Applications

Natural gas and air applications tend to have a low operating pressure, so proper sizing to reduce a pressure drop from inlet to outlet is important.

Frequently Asked Questions

Its easy to become overwhelmed when youre researching the best Y filter for your needs. To that end, lets take a look at a few common inquiries and how to solve them.

How Should I Install My Strainer?

Y strainers have an arrow from inlet to outlet. It is important to install them in this orientation for proper filtration.

What Kind of End Connections are Available?

Depending on your needs, Y filters can include a variety of end connections, including flanged, threaded and welded. You can also find special flanges, such as ring joints.

What Kind of Housing Material Should I Choose?

Depending on your environment and media, a different Y strainer housing material and seal material should be selected. Ensure you know the chemical resistance of them to select the proper one.

Are Y Strainers Affordable?

Yes! This type of strainer is also an affordable alternative to other types of strainers, made even more economical as you scale down in size. Considering they protect more expensive components, they are a good investment.

Should I Choose on My Own?

This article should help you select the proper Y strainer for your application. However, feel free to contact our technical support with any questions.

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Ball Valves vs Globe Valves,Which Valve is Best for You?

There are many different types of valves available for different applications. With so much choice it can be difficult to decide which valve is most suitable for your application. In this article, STV Supplies explores the merits of ball valves versus globe valves.

 

 

 

 

WHAT IS THE MAIN DIFFERENCE BETWEEN BALL AND GLOBE VALVES?

The main difference between ball and globe valves is the way they close. Ball valves have a stem and ball, which turns horizontally, and are commonly referred to as “rotational” valves. Whereas, globe valves have a stem and plug, which strokes linearly, and gives them their other name of “stroke” valves. Ball valves are best suited to applications requiring on/off control without pressure drop. While globe valves excel at regulating flow.

HOW DOES A BALL VALVE WORK?

Ball valves are designed with a ball inside the valve. A ball valve is a form of quarter-turn valve which uses a hollow, perforated and pivoting ball (called a “floating ball”) to control flow through it. It is open when the ball’s hole is in line with the flow and closed when it is pivoted 90-degrees by the valve handle. The handle lies flat in alignment with the flow when open, and is perpendicular to it when closed, making for easy visual confirmation of the valve’s status.

HOW DOES A GLOBE VALVE WORK?

Globe valves were for many years the industry standard in control valves. They 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 (or disc) can be screwed in to close the valve. Typically, automated globe valves use smooth stems rather than threaded and are opened and closed by an actuator assembly.

WHICH IS BETTER: A BALL VALVE OR GLOBE VALVE?

Ball valves are durable, performing well after many cycles, and reliable, closing securely even after long periods of disuse. These qualities make them an excellent choice for shutoff applications, where they are often preferred to gates and globe valves. On the flip side, ball valves do lack the fine control in throttling applications offered by globe valves.

STV SUPPLIES STOCKS BALL AND GLOBE VALVES

 

 

STV stock a wide range of ball valves, from quarter-inch to six-inch at our works in Bishopbriggs. From general purpose two-piece ball valves, v-ball control valves, hygienic valves, to heavy duty ball valves for steam; we have a variety of sizes, end connections and materials to suit many applications. We also stock globe valves up to six-inch in size, and can supply many size and material variants on a next-day basis.

What is a Gate Valve

The gate valve is a fairly common valve that can be seen in the piping systems of many homes and structures. It is the preferred valve for houses because it is rather easy for any homeowner to operate. It can also be used for more industrial purposes and are instantly recognizable.

Since this particular valve’s design is for it to either be opened all the way or closed all the way, the drop in pressure across the actual valve is extremely limited when opened, making it possible for fluid to flow through nearly seamlessly and the seal that exists between the valve’s disk and the valve’s seat is strong enough to resist any pressure that may be coming from the fluid.

Like with any other kind of valve, the gate valve has its advantages and disadvantages and recognizing what these are will provide any potential user the ability to make a better informed choice in what kind of valve they should use. Also, knowing the pros and cons can make the user know what to expect and what needs more looking after.

One of the advantages of gate valves is its high capacity as well as its ability to seal tightly, making the shutoff of any flow possible and any leakage nearly impossible. This particular kind of valve is also known to be very cost effective, which is probably why it is a popular choice for countless residences. Gate valves also have low friction loss because there is almost nothing obstructing the flow of the fluid when the valve is fully opened, creating little resistance to the flow.

As earlier mentioned, gate valves are meant to be fully opened or fully closed and partially opening the valve is bound to cause vibration which in turn leads to damage to the valve. Another thing that needs to be taken into consideration is that the valve disks and valve seats go through a great deal of wear and tear, making it necessary to replace them more often than compared to other kinds of valves. Because it is either fully opened or fully closed, gate valves are thought to have difficulty in controlling flow.

Overall, the gate valve remains a great choice as a control valve for any piping system that does not need to be constantly turned on or off. It is able to handle large flows of fluid, making it work for industrial purposes as well. Gate valves can also work with several materials such as oil, gas, air, steam, heavy and corrosive liquids, non-condensing gases, and slurries, making it a versatile selection.

The most important thing to remember when gate valves are used in a piping system is how it is maintained. According to an article entitled how to maintain a gate valve, the proper maintenance of gate valves can help ensure that they function properly and last for years so making sure that these valves are taken care of accordingly enables there to be more pros than cons.

 

To Understand About Parts Of A Ball Valve

While contemplating on the brand and type of ball valve to purchase for use in your shut off application or flow control system, be in the know of its various parts. Having an adept knowledge of its parts will give you an idea of how the valve entirely works when it is installed.

1. Body :

This part is regarded as the principal part of a valve, regardless of its shape and type. It is the part that gives framework to the whole valve because it holds all the other parts intact. It also serves as the pressure boundary of the valve because it is the first line of resistance against the volume and pressure of the liquid flowing through all the pipes connected to it.

2. Bonnet:

This part covers the opening in the valve’s body. It also serves as the second pressure boundary. Valve bonnets are usually bolted and screwed with the body. It is also usually made of the same material as the body to make the whole valve firmer and stronger.

3. Trim:

This part is a collection of differentinternal valve parts such as disk, seat, stem and sleeves. Because of these internal parts, the valve can perform basic motions to provide flow control. The disk together with the seat is important in determining the performance of the valve system. In most designs, the disk serves as the third layer of pressure boundary. It can permit and prohibit fluid flow due to its pressure-retaining capacity.

The seat, also called as seals ring provides an interface to where the disk is seated. The seal rings can either be forged within the body by welding or by machine. The stem is responsible for positioning the disk. It connects the actuator and the disk usually though welded joints.

4. Actuator:

This part works in conjunction with some internal parts located in the valve trim. This part is responsible for running the stem and disk. There are many types of actuator that are available in the market today. Some are handwheels, levers, motors, solenoids, pneumatic operators or hydraulic arms. Most valve manufacturers’ provide a design where the actuator is mounted with the bonnet through a yoke.

5. Packing:

This part commonly prevents leaks from the space between the valve stem and bonnet. The valve packing can be made from fibrous materials like flax or some other materials like Teflon. Regardless of the valve packing composition, it should be able to form a seal between the internal parts and the outer valve environment where the stem extends from the valve body. The packing must be properly placed to prevent leaks that can cause further damages to the entire valve system. The packing must neither be too loose nor too tight.

In summary, knowledge of the different parts of a ball valve will give you a generalized idea of how it will work during the entire span after it has been installed by your designated workforce. It will also help you to have a rough estimate of the cost of implementing a flow control system with the use of a ball valve.