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.
