What is a three-way globe valve?
A three-way globe valve is a special configuration of a double-seated globe valve. This type of valve has two basic types that is one type of three-way globe valve is used for mixing to combine two streams of fluid that flow to a common outlet port. The other type is used to diversion application by taking common stream and splitting it into two outlet ports. A representative of a mixing application is combining two different liquids to create a specific outlet product. On the other hand, a diverting three-way globe valve can be used to switch a stream of fluid from one vessel to another vessel. The diverting valve is also used in the control of temperature in a heat exchanger. When controlling temperature, the three-way globe valve directs one portion of fluid flow via the exchanger and the balance of the fluid flow bypasses the exchanger. The respective fluid split provides the heat balance required to control the temperature. In a three-way globe valve, the forces that act on the double seat do not balance similar to the two-way double-seated valve. This is because the three-way globe valve has different pressure levels in each flow channel. In addition, the three-way globe valve has a different dynamic force that acts on each plug head. As such, a three-way globe valve should not be used where there is a high-pressure drop.
Figure: Three-way globe valve
Components of a three-way globe valve
The actuator is the source of power for closing or opening the valve. Several types of actuators can be used in a three-way globe valve that is manual, pneumatic, hydraulic, and electrical actuators.
Bonnet is the component of a three-way globe valve that connects the valve body to enhance tight closure free from leakage. The bonnet used in a three-way globe valve can be bolted (uses bolts and nuts) or screwed (uses screws). Each of the two bonnet types has its benefits for example the screwed bonnet offers a pressure-tight seal. The bolted bonnet is best for three-way globe valves that are working at very high pressure.
Three-way globe valve packing is a gasket used to enhance the tight seal between the bonnet and valve stem. It is used to keep fluids from leaking out of the stuffing box and stems. It has gland followers which are tightened to ensure there is no leakage. The packing of the three-way globe valve can be made of different materials such as elastomers, PTFE, fibrous materials among others. The packing of the three-way globe valve needs to be manufactured in a way that will help to reduce the risk of stem damage and consequently fluid leakage.
This is the component of a three-way globe valve that seals the space between the stem and plug and bonnet. The seat ring is screwed or torqued into the valve. The seat/seat ring provides a replaceable and stable shutoff surface.
The stem connects the actuator to the disk to help in transmitting force to control flow via the valve. The stem of a three-way globe valve is used to position the disk properly and provide the necessary motion on the plug to close or open the valve. The stem is one of the main components of a three-way globe valve since it connects the internal components of the valve and the actuator. To prevent fluid from leaking, the valve stem is provided with packing around it. The packing around the stem should be replaced as recommended by the three-way globe valve manufacturer. The stem is made of strong materials like steel to help it withstand high pressure and stresses in the valve during operation.
The plug is another very important component of a three-way globe valve. It is also known as a disk. The plug sits on the seat when the valve is closed blocking the fluid flow. When the plug sits above the valve seat it allows fluid flow.
The valve body of a three-way globe valve is the component that holds all the other components together. The valve body houses all the internal components of the valve to allow fluid control. The valve body has the three ports required in a three-way globe valve.
Figure: Components of a three-way globe valve
Working principle of a three-way globe valve
The working of a three-way globe valve depends mostly on the use of that valve. These valves are mostly used for mixing or diverting the fluid flow. So the working principle of a three-way globe valve will depend on its use as discussed below.
Three-way globe valve used for mixing application
When a three-way globe valve is used for mixing application, fluid from inlet ports A and B are mixed in the valve body. After being mixed, the fluid is transmitted via the outlet port AB. Mixing the two fluids at different pressure and temperatures helps to enhance required properties and send them for indented use.
Figure: Working of a three way globe valve for mixing application.
Three-way globe valve used for diverting flow
A three-way globe valve used for diverting flow has AB as the inlet port while A and B as the outlet ports. When the spindle and plug are at 100% upwards, port A becomes blocked. This allows fluid flow from AB to B only. When the spindle and plug are 100% downwards, the fluid flow via B is blocked. As such, flow occurs only from AB to A.
Figure: Working of a three way globe valve used for diverting application.
Three-way globe valves can also be used as bypass valves in both primary and secondary loop valve applications.
Types of three-way globe valve
There are two types of three-way globe valves based on the application that is diverting and mixing three-way globe valves.
Diverting three-way globe valves
These are three-way globe valves used for diverting the fluid flow. These valves have two outlet ports and one inlet port. The movement of the valve stem displaces two plugs. Based on the plugs and seat geometry, the incoming fluid flow is distributed into two outgoing lines. These valves have a common stem that is used to operate two plugs for two outlets. Diverting three-way globe valves are used in several applications such as large air handling units for cooling or heating. These valves are also used in a hydronic system that has variable flow. Diverting three-way globe valves should be mounted with the stem vertical above the valve body to help enhance its life. Three-way globe valve manufacturers make these valves using strong materials in different components of the valve such as valve body, stem, and plugs. These strong materials are meant to help the valve overcome high pressure emanating from high fluid pressure. Such strong materials include stainless steel and brass. These materials are also used to protect the valve from corrosive and abrasive media that can easily damage the valve.
Mixing three-way globe valves
A mixing three-way globe valve is a valve used for mixing applications. This valve is used where one wants to mix two fluids of different pressure and temperatures or other characteristics but ends up with a fluid having the same properties at the valve outlet. These valves can work with several actuators such as pneumatic, electrical, manual, or hydraulic actuators. These valves are direct-coupled and have a universal bonnet. These valves are made of strong materials such as stainless steel. The strong material helps to overcome fluid flow pressure and temperature. A combination of high pressure and temperature can easily weaken the valve so strong materials are always used by three-way globe valve manufacturers.
Features of a three-way globe valve
- Three-way globe valves employ top entry design easing inspection and maintenance.
- Three-way globe valves can work on different types of actuators as per customers’ preferences.
- They have balanced trim that allows for high fluid flow rates while reducing the size of the actuator.
- Three-way globe valves have excellent fluid flow control rangeability.
- These valves can mix different fluids into one fluid component.
- These valves can divert flow from one direction to another.
- These valves can restrict fluid flow.
What should you consider when selecting/purchasing a three-way globe valve?
Different three-way globe valves are designed to withstand different levels of pressure. Understanding the working pressure requirement in the pipeline will help to determine the valve that can withstand such pressures. A valve working at high pressure than its strength can cause leakages as well as get damaged.
Three-way globe valve manufacturers make the valves targeting different operating temperature levels. Some materials such as PTFE can withstand low temperatures while materials like stainless steel can withstand high temperatures like 400 oC. As such, knowing the fluid working temperature will help to select the right valve for the right task. Using a valve for the wrong temperature can easily damage the valve even during the first day of use.
Materials used to manufacture the valve
Three-way globe valves work on different fluids and materials that have different properties. The nature of the material used to make internal components of the valve will determine which fluids the valve can be used to work on. So, know the nature of the fluid to work on to help you best select the right three-way globe valve for that task. Some fluids are corrosive and thus they need corrosion-resistant materials like PTFE.
Knowing the fluid flow coefficient is important as it will help to determine the ideal three-way globe valve that can optimize the flow process.
Type of actuator
The actuator is the component that will provide the power to run the valve. The available actuators that can be used on a three-way globe valve are manual actuator (it is powered by hand using a handwheel), pneumatic actuator (it is powered by compressed air to help drive the closing and opening valve mechanism), electrical actuator (it uses electricity to control the valve) and hydraulic actuator (it uses hydraulic fluid such as oil or water to close or open the valve). Some actuators are cheaper and more convenient to use than others. The type of actuator depends on the customer’s preference for ease and speed of use.
Applications of three-way globe valve
- Three-way globe valves are used in air separation.
- They are used in natural gas processing.
- They are used in the liquefaction of liquefied natural gas.
- Three-way globe valves are used in wood processing.
- They are used in water treatment.
- They are used in food processing and production.
- Three-way globe valves are used to enhance constant flow in heat exchangers.
- They are used to enhance the constant water supply and temperature in a refrigeration-condensing unit of a heat exchanger.
Advantages of a three-way globe valve
- Three-way globe valves are easy to inspect and do maintenance.
- Different actuators can be used on three-way globe valves.
- These valves have good flow control rangeability.
- These valves have excellent pressure capability.
- These valves can work in a wide range of temperatures.
- These valves are resistant to corrosion.
Disadvantages of a three-way globe valve
- Three-way globe valves are expensive relative to other valves.
- Three-way globe valves have a high weight.
- They have a high-pressure drop.
Troubleshooting three-way globe valves
Leakage from stem packing
- Loose packing flange. Fasten packing flange.
- Stem is damaged. Disassemble the three-way globe valve and visually inspect it. Verify if plug parts are damaged and replace if necessary.
- Stem not damaged. Replace O-rings and packing rings of gland flange considering all the safety procedures recommended by the manufacturer.
Excessive internal leakage when the three-way globe valve is closed
- Check supply of air pressure into the valve to be as recommended by the three-way globe valve manufacturer.
- When the valve is in a closed position. Check if the positioner output pressure scale is identical to the recommended pressure.
- Adjust the valve’s stroke to make it close securely and reassemble the clamp.
Leakage from the bonnet
- Bonnet is not properly tightened. Tighten the bonnet.
- Disassemble the three-way globe valve and check the gasket on the bonnet.
The handwheel actuator cannot turn flexibly or the disc cannot close or open
- Packing is over tightened. Loosen the packing nuts.
- Crooked gland. Rectify the gland.
- Damaged stem nut or presence of dirt. Check the stem nut screw threads. Clean the dirt.
- The stem has a bend. Replace or rectify the stem.
- Worn out screw threads on the stem nut. Replace the stem nut.
Three-way globe valves are globe valves that have three ports. These valves are used in diverting or mixing fluids. When used to mix fluids, the valve employs two inlets and one outlet port. When used to divert fluid, the valve employs one inlet and two outlets. Three-way globe valves are globe valves that have the seat at the bottom of the valve body. These valves have their third port located normal to the other two openings. Three-way globe valves are of two types that is the diverting version and the mixing version.
Three-way globe valves are used in different applications such as control of water, oil, and gas processing, in cooling and heating applications such as heat exchangers, air separation, and food processing among others. Three-way globe valves have common features such as top entry design, compatibility with different actuators, have wide control rangeability, and the ability to divert and mix fluids. Before purchasing/selecting a three-way globe valve you need to consider certain factors which are pressure rating, operating temperature, flow coefficient, type of actuator, compatibility of the media, and the valve materials. Three-way globe valves advantages include ease to inspect and do maintenance, good pressure capability, resistance to corrosion, and a wide range of temperature levels.