,

What is a three-way valve?

A three-way valve is a valve that has three ports. These valves are commonly used in different applications to mix or divert fluids. When used to mix fluids, two fluid streams combine to form one outgoing stream. When used to divert fluid, one fluid stream is separated into two outlet streams. A three-way valve is controlled as per the spool shape. These valves are mainly used to change fluid flow direction. Three-way valves are of two types that is the T-port and the L-port. The L-port valve can enhance flow in one way or the other as well as shut flow completely. On the other hand, a T-port can perform the same flow task similar to the L-port valve but it does not shut off. Three-way valves are very common in the market as they easily control flow paths and fluid shutoff in one valve body. Also, these valves are cost-effective in directing the flow and shutoff of fluids. Three-way valves are commonly used to completely restrict flow, mix flow, and divert flow. Three-way valves are mostly used in high-pressure applications like boiler feed water used in steam power plants, food processing, and oil and gas separation among others. 

How does a three-way valve work? 

Two common types of three-way valves are the L-types and the T-type. The L-type of the three-way valve is also known as the diverter three-way valve. This valve diverts flow from one port to another port by rotating handle (for manual valve) or by using a rotating actuator to 90o. If the left port and bottom port are opened first, then a quarter-turn of the valve in the counterclockwise direction makes the three-way valve divert the fluid flow to the outlet port. When the handle or actuator is turned again to make 180o turn, it blocks the flow of the fluid. Also, if it is turned to make 270o turn it will still block fluid flow. When the valve completes 360o turn it returns to the original position. This makes the L-type of the three-way valve have two ports available at once as well as have three flow and two shut-off position choices. The T-type of the three-way valve is the mixing type. This valve works to mix two flows from the inlet. T-type can have its three ports open at one time. This helps the valve to separate the fluid into two opposite directions. The design of a T-type three-way valve divides the flow or makes straight-through fluid flow. 

Configurations of T and L type of three-way valves

Types of three-way valves 

L-type three-way valve 

This is a three-way valve mostly used to enhance fluid flow from a single inlet port to either of the two outlet ports. This type of three-way valve helps to divert fluid flow making them be known as diverter three-way valves.

L-type three-way valve configurations

T-type three-way valve 

The T-type of a three-way valve is commonly used to mix two streams of fluid from the inlet into one stream to the outlet port. These valves are also designed in a way that makes them do fluid diversion just like the L-type of the three-way valve. T-type three-way valve design can also have mixing flow, diversion flow, and straight through fluid flow depending on the allowable motion of the handle. 

T-type of three-way valve configurations

Floating three-way valve 

This is a type of three-way valve which uses a floating ball. The ball is held in position by compression of two seats. The ball is free to rotate within the valve body. A floating three-way valve is capable of allowing bidirectional shut-off. However, when there is high pressure upstream, it is difficult to operate the valve. 

Forged three-way valve 

This is a three-way valve made using the forging manufacturing process. Forged three-way valve manufacturers use materials like steel alloys to make these valves. The forging process makes the material grain structure more refined which helps to increase the strength of the valve material. These valves have very high strength which makes them suitable for high temperature and high-pressure applications. Also, by using the forging method, these valves have enhanced resilience to common problems like shrinkage, porosity, and cracks. 

Cast three-way valve

These are three-way valves made by using the casting method. This method employs molten metal to manufacture the valves. The molten metal is poured into a mould of various sizes and shapes. The mould is given time to cool and solidify whereby after cooling the valve is produced. This method of producing cast three-way valves has the advantage of making valves of complex designs, shapes, and sizes. This method helps to make valves with critical parts such as the three-way valves. 

Manual three-way valves 

These are valves that operate manually by use of a handwheel or using a hand lever. The mechanical lever or handwheel helps to transmit torque from the valve operator to the stem and finally to the opening and closing mechanism of the valve. 

Actuated three-way valves 

These are three-way valves that work by using a mechanical system that provides torque to close/open the valve. The source of power for these valves can be pneumatic, hydraulic, or electrical.

Components of three-way valves

Valve body 

This is the component of a three-way valve used to house internal parts of the valve-like seat, ball, and disk depending on the type of valve. The valve body helps to enhance strength for the valve. The media flow is controlled through the valve body. Pipes in a three-way valve are connected to the valve via the valve body. The valve body needs to be very strong to help contain the high pressure and temperature associated with the fluid or media flow. The valve body strength depends on the material used. Metallic materials such as steel are known for being very strong relative to other materials such as PFTE. The valve body is made using production methods such as casting or forging using materials like stainless steel, cast steel, alloy steel among others. 

Bonnet 

The bonnet is another component of a three-way valve used to retain pressure. The bonnet is connected to the body to enhance tight valve closure to prevent fluid leakage. The bonnet is mounted on the valve body using bolts or screws. The bolted bonnet is mostly used where the three-way valve will work at very high pressure while the screwed bonnet is used to provide a tight seal to deter fluid leakage. 

Stem 

The stem is the component of a three-way valve that is used to transmit power to the valve plug, disc, or ball to open or close the valve for fluid control. The stem gets power from the valve actuator, handwheel, or lever. In some three-way valves such as globe or gate valves, the stem employs linear motion to close/open the valve. In other three-way valves, the stem uses rotary motion such as in ball and plug valves to open/close the valve. 

Valve seat 

The valve seat is the part that helps to seal space between plug/ball and stem depending on the type of the three-way valve. 

Trim 

Trim is a term that refers to the internal components of a three-way valve that comes in contact with the fluid. Such parts of the three-way valve include the seat, glands, disc, bushing, spacers, and ball. These components are important depending on the type of the three-way valve as without them the valve would not work. 

Actuator 

An actuator is the component of a three-way valve that provides a mechanism and power to operate the valve. The actuator is connected to the valve stem and disc. The actuator can be manual with a handwheel, gear, lever, chain or be powered by an electric motor, pneumatic or hydraulic fluid.

Features/characteristics of three-way valves 

  • Three-way valves can close or open without friction. 
  • Three-way valves employ top entry design for ease of inspection and maintenance. 
  • These valves need low torque to operate with a small handle. 
  • Three-way valves are self-cleaning.
  • Three-way valves have a wedge sealing design. 
  • Three-way valves can divert fluid flow. 
  • Three-way valves can mix fluids at different temperatures and pressure to one stream. 
  • Three-way valves have balanced trim able to enhance high fluid flow. 
  • Three-way valves can shut off fluid flow. 

 

Selecting/purchasing and sizing of three-way valves 

The selection of a three-way valve depends on certain parameters/factors discussed below.

Fluid being controlled 

Different fluids have different chemical properties such as being corrosive like acids. Such fluids need to work on a three-way valve that is resistant to corrosion. If the valve used cannot resist corrosion, its internal components coming into contact with fluid can easily get corroded and consequently destroy the valve. 

Maximum pressure 

This is the highest pressure that the three-way valve is expected to experience. Pressure is a very important consideration as pressure is one of the parameters that can easily damage a valve and cause leakage. If the valve used cannot withstand the maximum pressure the valve body can be damaged. In addition, excess pressure can cause fluid leakage. Some fluids are very destructive and leaking such fluids to the environment can lead to prosecution of the organization using that valve. 

Maximum temperature 

The working temperature needs to be known before purchasing/selecting the three-way valve. A three-way valve can work best if the valve is made of materials that can withstand the working temperature. Materials such as PFTE have low temperatures when compared to metallic materials such as cast iron and stainless steel. So, a valve whose internal parts are made of low temperatures like PFTE and other plastics or rubber should only be used where the maximum temperature will not melt or damage the materials. If the temperature is high, it will cause thermal distortion to the material and thus cause valve damage. 

Actuator 

The actuator type affects the three-way valve in different dimensions. Some actuators are cheap like pneumatic actuator that uses compressed air. Other actuators like manual handwheel are the cheapest as they do not have running costs like electrical actuators. The electric actuator is cheap to install but its running costs are high. Some actuators like pneumatic, hydraulic and electrical actuators can be automated or semi-automated to reduce manual labor. 

 

Applications of three-way valves 

  • Three-way valves are used in water treatment. 
  • Three-way valves are used in food and beverages processing. 
  • Three-way valves are used in pharmaceutical industries. 
  • Three-way valves are used in processing natural gas. 
  • They are used in air separation. 
  • These valves are used in water treatment. 
  • Three-way valves are used in heating, ventilation, and air-conditioning. 
  • They are used in wood processing. 

 

Advantages of three-way valves 

  • Three-way valves are of low fluid resistance. 
  • These valves are of lightweight, simple design, and low volume. 
  • Three-way valves have reliable sealing. 
  • Three-way valves have a convenient operation as they can close or open rapidly. 
  • They are convenient for maintenance due to their simple design. 
  • These valves have a wide range of applications. 
  • Three-way valves are resistant to corrosion. 
  • Three-way valves have a wide range of operating temperatures. 
  • These valves have a wide range of operating pressure. 
  • These valves can work on manual, pneumatic, hydraulic, or electrical actuators. 
  • Three-way valves are cost-effective relative to the work they can do. 

 

Disadvantages of three-way valves 

  • Three-way valves tend to have a high weight relative to other valves. 
  • The cost of manufacturing three-way valves tends to be higher relative to other valves because of their involving working mechanism. 
  • Three-way valves have a high-pressure drop. 

 

Troubleshooting three-way valves 

Three-way valve leakage 

  • Damaged seats. Replace the seats. 
  • Damaged ball surface. Replace the ball. 
  • Incomplete valve closure. Check closing/opening settings and limits. 
  • Bonnet is loose. Tighten the bonnet nuts or screws. 

Irregular ball movement 

  • Dirt between seats and ball. Flush the inside of the valve several times to remove the dirt. 

Valve torque is very high 

  • Damaged seat. Replace the seat. 
  • Excessive temperature or pressure. Ensure the working conditions are as recommended by the three-way valve manufacturer. 
  • Dirt between seats and ball. Flush the inside of the valve to remove the dirt. 

Stem leakage 

  • Loose stem nuts. Tighten the stem nuts.
  • Stem seals damaged. Replace the seals or seal with sealant grease. 
  • Seal surfaces damaged. Replace the sealing surface. 
  • Mechanical damage on the stem. Replace the stem. 

Leakage in the body seal

  • Damaged gasket. Replace the gaskets. 
  • Excess load from the pipeline. Check the piping architecture is recommended by the three-way valve manufacturer. 
  • Excess temperature or pressure. Check the working temperature/pressure is as recommended by that particular three-way valve manufacturer. 

Excess noise from the three-way valve  

  • Wrong valve sizing. Ensure valve size matches the piping and load. 
  • Incomplete opening. Ensure the opening/closing settings and limits.

Summary 

Three-way valves are valves that have three ports. These ports help three-way valves to enhance variable flow in the piping system. These valves are used to shut on/off, divert, and mix fluids in piping systems. When used as mixing valves, these valves combine two fluid streams to form one fluid stream. When used as diverting valves three-way valves, one fluid stream is separated into two fluid streams.

There are several types of three-way valves but the main two types are the L-type port and the T-type port. L-type valve is used to divert fluid. A T-type of valve is used to mix and shut off fluid flow. Three-way valves are used in many applications such as diverting water in feed water in steam power plants, pharmaceutical, oil and gas separation, water treatment, food processing among others. 

The common features/characteristics of three-way valves are simple and lightweight design, self-cleaning, and a wide range of temperatures and pressures. When selecting a three-way valve it is important to consider important such as operating temperature, nature of the fluid, pressure rating, and type of actuator. 

 

/by

What is stainless steel gate valve?

A stainless steel gate valve is a type of gate valve which is made entirely of stainless steel material. A stainless steel gate valve is known for its high strength. With that high strength, these valves are suitable for high pressure and high-temperature applications. Stainless steel gate valves are also known to be made of tough bodies, more durable relative to other valves like ductile iron and cast iron valves. Stainless steel gate valves are also known for their corrosion resistance. A combination of corrosion resistance, high strength, and high toughness makes stainless steel gate valves very useful in all high-pressure applications. However, stainless steel gate valves are expensive because the machining of stainless steel is difficult to shape and takes a lot of energy. 

As the name suggests, stainless steel gate valves have a gate to control fluid flow. Stainless steel gate valves are used to control fluid flow by either closing or opening a gate. The process of opening or closing the gate is linear and the gate travels vertically upwards or downwards to open or close the valve respectively. Stainless steel gate valves are not used to regulate fluid flow because this causes its gate to get damaged easily. They are only used to close or open fluid flow. Stainless steel gate valve manufacturers design the valve such that the gate is perpendicular to the fluid flow. This design helps to reduce pressure loss. Stainless steel gate valves are bi-directional which makes them be installed in almost any direction. 

Components of a stainless steel gate valve

Handwheel/actuator 

The handwheel is a component used in manual stainless steel gate valves so that the valve operator can apply torque to open/close the valve. If the stainless steel gate valve is not manual, then it is operated by an actuator. An actuator is a device used in stainless steel gate valve to provide torque to open/close the valve. When the handwheel/actuator rotates, it helps to rotate the stem which is connected to the gate. Thus handwheel works with a stem to open/close the stainless steel gate valve. 

Valve body 

The valve body in a stainless steel gate valve is the main component used to house internal parts of the valve. This component of a stainless steel gate valve is made of stainless steel material. Stainless steel is known to be strong and tough and thus it helps to protect the valve against damage in times of very high pressure and high temperature since these valves are mostly used in high pressure and high-temperature applications. 

Bonnet 

This is a component used to cover the top of the stainless steel gate valve. The bonnet is placed on the top of the valve body and the two are connected using screws or bolts. The screws and bolts help to enhance a tight seal free from fluid leakage. Between screw and bolted connection, the bolted connection is mostly used since it can provide a tighter seal at very high pressure. Another method of connecting the bonnet and the valve body is by welding. The welded bonnet is superb as it provides zero leakage seal. The bonnet is also made of stainless steel material like the valve body which enhances valve strength.

Stem 

This is the component of a stainless steel gate valve which is connected to the handwheel and the gate/disc. The stem is meant to transmit torque from the handwheel through its threads to the gate. This torque is then converted to linear force which is used to raise or lower the gate to open or shut off fluid flow. The stem needs to be strong to enhance its ability to transmit torque to the gate. As such, the stem in a stainless steel gate valve is made of stainless steel to enhance its strength. 

Gate 

A gate in a stainless steel gate valve is an internal component that is tasked with blocking or opening fluid flow. The gate used in stainless steel gate valves can be either wedge or parallel-shaped. 

Seat 

The seat is an interior component of a stainless steel gate valve. Stainless steel gate valves are designed with two seats to ensure a tight seal with the gate. Seats used in stainless steel gate valves are integrated with the body or they are in terms of a seat ring. For seat rings in stainless steel gate valves, they are pressed or threaded into position and seal welded to the body. Integrated seats are valves made of the same material (stainless steel) as the body. Threaded in or pressed in seats allow for variations such as the seat can be made of different materials like PTFE instead of stainless steel. 

Backseat 

The backseat in a stainless steel gate valve is mounted in the bonnet. The backseat helps when the valve is opened fully so that the valve stem can “back seat” against the bonnet to help close off fluid pressure to the stuffing box. This helps to support the main seal on a stainless steel gate valve which is often a stuffing box. 

Trim 

Trim is a name given to the internal components of a stainless steel gate valve. The components under trim include gaskets, seat, seating surface, gate, gate surfaces, seals, stuffing box, and bushing. 

How does a stainless steel gate valve work? 

Stainless steel gate valves work by turning a handwheel to either open or close fully. When the handwheel is rotated, it rotates the stem. The stem is connected to the gate/disc. As the stem rotates through its threads it helps in raising or lowering the gate/disc. When this gate raises upwards it opens the valve allowing fluid to flow. When the gate is lowered it closes the fluid flow. Opening of stainless steel gate valve occurs when the handwheel is rotated anti-clockwise while closing occurs when you rotate the handwheel in a clockwise direction. 

Working of a stainless steel gate valve

Types of stainless steel gate valves 

Rising stem stainless steel gate valve 

This is a stainless steel gate valve in which the stem can move upwards when the valve is opening. Using this type of stainless steel valve, the valve operator can monitor the closing of the valve and thus easily know when the valve is fully closed/opened. This is because when the stainless steel gate valve is fully opened the stem will be exposed above the handwheel. 

Non-rising stem stainless steel gate valve 

This is a stainless steel gate valve that has a blind stem. The stem in this type of gate valve turns to close and open the valve but it does not move down or up as it turns. When the stem in a stainless steel gate valve rotates, it moves in or out of the valve. As such, the gate moves proportionately to close or open the valve. This type of stainless steel gate valve is used in several applications such as water supply, HVAC, gas, steam, and other utility applications. Non-rising stem stainless steel gate valves operate in small spaces relative to rising stem counterparts. 

Stainless steel knife gate valve 

This is a stainless steel gate valve design that reduces contact between various valve components. As such, this stainless steel knife gate valve helps to reduce the wear and tear of its parts in contact. Stainless steel knife gate valves are used for closing/opening services in applications with high levels of suspended solids. These valves are suitable for handling corrosive, slurry, viscous, and abrasive fluids. Stainless steel knife gate valve is easy to operate and it has low weight.

Stainless steel flexible wedge gate valve 

This is a stainless steel gate valve with a solid gate and a cut around the perimeter. The cut is of different sizes, shapes, and depths. When the cut is narrow and shallow it offers high strength but low flexibility. When the cut is wide and deep it reduces strength but enhances flexibility. Stainless steel flexible wedge gate valve design has enhanced seat alignment and better leakage tightness. These valves are used in different applications such as steam systems. Stainless steel flexible wedge gate valves allow the gate to bend when the seat is compressed during the thermal expansion in steam application. This helps to prevent thermal blindness. 

Stainless steel wedge gate valve 

This is a stainless steel gate valve that uses a wedge-shaped gate/disc. When a stainless steel wedge gate valve closes, it does so by pushing the gate to a taper machined on the valve body. The seal becomes better by combining the gate wedge shape of the body with a seat ring. When a stainless steel wedge gate valve opens fully, the back seat enters into a bonnet bush. For actuated valves, the stem does not keep wholly on the back seat to prevent damage. 

Stainless steel slab gate valve

This is a stainless steel gate valve that is unitary with a bore-size hole. When a stainless steel slab gate valve is opened, the holes are coincident with two seat rings. Such orientation in a stainless steel gate valve helps to produce even media flow with minimal turbulence which helps to reduce system pressure loss. Stainless steel slab gate valves need their seats clean. However, the gate cavity can at times be clogged with debris. As such, stainless steel slab gate valves are designed with a plug used for expelling the debris during maintenance. Stainless steel slab gate valves are suitable for transporting crude oil and natural gas liquids. 

Stainless steel parallel slide gate valve 

This is stainless steel gate valve that does not require a wedging action for proper seating. The stainless steel parallel slide gate valve closes using two individual gates connected via a disc holder. Springs in parallel move down to close the valve. When the port seals, the stem plug prevents additional movement. When the valve is open, the gate moves upwards, and the stem sits back. Stainless steel parallel slide gate valve close and open fully with limited movement. 

 

Applications of stainless steel gate valves 

  • Stainless steel gate valves are is used in chemical plants. 
  • Stainless steel gate valves are used in transporting crude oil and natural gas liquids. 
  • These valves are used in pipeline industries. 
  • Stainless steel gate valves are used in slurry applications. 
  • They are used in liquids, gas, and steam applications. 
  • Stainless steel gate valves are used in the control of hydrocarbons, feedwater, air, and fuel gas applications. 
  • Stainless steel gate valves are used in high pressure and high-temperature applications. 
  • Stainless steel gate valves are used in food processing and beverages applications. 
  • These valves are used in the heating, ventilation, and air conditioning (HVAC) systems of buildings.

 

Advantages of stainless steel gate valves 

  • Stainless steel gate valves have low small fluid resistance. 
  • It requires a small force to open and close the valve. 
  • Stainless steel gate valves are bi-directional. 
  • Stainless steel gate valves are very strong for high-temperature and high-pressure applications. 
  • Stainless steel gate valves can be manual or operated by an actuator. 
  • Stainless steel gate valves get less erosion on the sealing surfaces by the flowing fluid when they are fully open relative to stop valves. 
  • Stainless steel gate valves have a relatively simple body design for ease of repair, cleaning, and maintenance. 
  • Stainless steel gate valves are of different varieties which makes them serve in many applications. 

 

Disadvantages of stainless steel gate valves 

  • Stainless steel gate valves open and close slowly. 
  • Stainless steel gate valves need a large area for operation, maintenance, and installation. This is because the stainless steel gate valve’s overall height and dimensions are large.  
  • Stainless steel gate valves tend to make a lot of vibrations and noise while in use. 
  • Stainless steel gate valves use two sealing surfaces which makes it difficult to process, grind, and do maintenance. 

 

Troubleshooting stainless steel gate valves 

Stainless steel gate valve leakage 

  • Leakage past packing after installation. This could be due to the stainless steel gate valve having been subjected to high temperatures during shipment. It could also be due to normal packing wear. Tighten the packing or replaced it as necessary. 
  • The stainless steel gate valve is leaking past its seat. Gate or seat is damaged. Replace the gate or seat as necessary. 
  • Leakage past the seat. Worn out the seat or worn out O-ring seal. Replace the seat or the O-ring seal as necessary. 
  •  Leakage in the seat. Foreign materials stuck in the gate. Remove the materials by flushing dirt through the valve. 
  • Leakage through bolted connections. Check loose body to bonnet connections. Tighten the connections (bolts, nuts, screws) as necessary. 

The excess force needed to open/close the stainless steel gate valve 

  • The valve needs lubrication. Check recommended lubrication by the stainless steel gate valve manufacturer. 
  • Misalignment between gate and stem. Loosen the valve yoke and handwheel/actuator and check the stem and gate alignment. Correct any misalignment and then tighten again. 
  • Stainless steel gate valve packing is very tight. Loosen the packing. Follow stainless steel gate valve manufacturer’s instructions in regards to tightening the packing. 

 

Summary 

A stainless steel gate valve is a gate valve that has most of its components made of stainless steel. Stainless steel is a metallic material known for its high strength and toughness. As such, gate valves made using stainless steel are of high strength and more durable. Stainless steel gate valves use a gate that is tasked to block or open fluid flow. These valves work by using a handwheel/actuator which transmits torque to the gate through a component known as a stem. When the actuator/handwheel is rotated anticlockwise it raises the gate and thus opens fluid flow. When the stainless steel gate valve is rotated clockwise, it lowers the gate and thus blocks fluid flow. Stainless steel gate valve manufacturers design the valves in a way that makes the gate and fluid flow perpendicular to each other in a straight flow path. This helps to reduce pressure drop in the valve since fluid flow in a straight line has a low-pressure drop. 

Stainless steel gate valves are used in different industries such as chemical industries, petroleum, water supply, food and beverage processing, HVAC systems, among others. Stainless steel gate valves are mostly preferred due to their superb features and advantages which are very strong, simple design, bi-directional capability, suitable for different actuators, small pressure drop, low fluid resistance, and ability to work at high temperature and high pressure. 

 

/by
,

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. 

 

/by
,

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.

 

/by
,

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.
/by