A 3-way control valve shuts off water flow in one pipe while opening water flow in another pipe. In a modulating or 3-point floating application the valve can also mix water from two different pipes into one pipe or divert water from one pipe into two different pipes. Connected to the Building Automation System and thermostats located in each zone, the 3-way valve directs the heating or cooling water through the coil if heating or cooling is required. If the zone does not need heating or cooling the flow is directed through the bypass line to the return piping. This means the flowrate will stay the same if you use 3-way valves in a system. In comparison a 2-way valve can stop water flow to the coil when there is no need for heating or cooling. This means the flowrate will vary if you use 2-way valves in a system.
Historically 3-way valves were used in constant flow pumping systems to maintain the same flow at all times whether there was a need for heating/cooling or not. Most systems today use 2-way valves for variable speed systems because the flowrate can fluctuate as valves open and close. As the 2-way valve closes the pressure differential increases and the pump slows down (less flow) which saves energy.
Most experts agree that variable flow pumping systems are preferred because they have the potential to save building owners significant pump energy cost. Some have switched their constant speed system to variable speed but they don’t capture the energy saving because they leave their 3-way valves or install 2-way valves and have overflow and underflow issues. With 3-way valves the variable speed system never experiences any energy savings because the 3-way valves maintain constant flow regardless of load changes and the pump can never reduce speed. When simple 2-way valves are installed there can be overflow and underflow conditions during start up and when valves are oversized which also wastes pump energy. Both of these problems can be solved by installing Pressure Independent Control Valves (PIC-V). A PIC-V maintains correct flow through each circuit or coil at all times even if the system pressure changes. The circuit has the exact flow it needs at start up, at design load and at reduced load. The flow is only changed when the control system requires a change.
No other control valve can deliver exact flow regardless of pressure changes. And if you are retrofitting your 3-way valves select a lower flowrate for the coil to provide a higher ΔT across coil. This reduced flow means the pump can reduce the speed and save energy.
There are challenges when all of the 2-way valves are shut off in a variable speed system:
Therefore it is good practice when converting from a 3-way system to 2-way system to leave the most remote 3-way valve in place on each riser so that cooling/heating water can recirculate even if all the other valves are closed.
Another issue with using 3-way valves in any type of application is they contribute to low ΔT syndrome. 3-way valves bypass conditioned heated/cooled supply water into the return line. The temperatures mix and the ΔT across the chiller or boiler is reduced because the supply water is mixed into the return.
How does a Pressure Independent Control Valve work in your system? A PIC-V combines a differential pressure regulating diaphragm with a 2-way actuated control valve to supply a specific flow regardless of system pressure fluctuations. The valve performs the function of a balancing valve and control valve in one unit. The actuator modulates the PIC-V to a required fixed flow based on load or zone requirements, independent of pressure.
When the zone is satisfied the actuator stops rotating and the valve is now set at optimum flow. If the system pressure changes the internal pressure regulating diaphragm compensates for the pressure change and maintains constant flow rate without cycling by the actuator. The flow does not change until the control system tells the actuator to change the valve position based on load changes. This stable flow means less work for the actuator, and actuator life is therefore increased.
To understand the "T"-port and an "L"-port 3-way valves and what makes them different, it's important first to establish what each of these terms mean. By clearly defining each term, the difference in directional flow purpose will be easier to understand. First, let's define exactly what a diverter valve does.
In simple comparison, a 3-way valve has one more port than a 2-way valve. But why? A two-way valve allows fluid to enter the valve from one port, and exit through the other. Having a third port, allows fluid an alternate path of travel, either when exiting or entering the valve. This permits fluid to either exit the valve from more than one point, or enter the valve from more than one point.
Several industrial applications use 2-way valves that provide on/off fluid service. Applications that require constant flow utilize 3-way valves, which contain three connection ports, having A, B and AB labels. 3-way valves can divert fluid flow to two directions or mix fluids from two different sources.
When using 3-way valves for mixing, fluids enter the valve body through ports A and B. The service fluids with different physical or chemical properties mix within the valve body before transmission through the outlet port AB. 3-way mixing valves are vital for combining liquids or gases with different temperatures and pressure, before sending them through the outlet with the desired properties.
For 3-way diverting valves, port AB acts as the inlet, while ports A and B become the outlets. Turning the spindle directs the flow to the left or right, upwards or downwards, depending on the orientation of the piping system. When flow moves from AB to A, the valve blocks fluid flow to port B. Changing the position of the spindle redirects the flow of fluids from AB to B and blocks the flow to port A.
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3-way valves are available in two internal structures. They are either L-type (L-port) or T-type (T-port) valves. The internal structures of the valve determine the flow patterns past the valve body. The T-port design is suitable for distributing common inlets to different destinations and the L-port design facilitates mixing from multiple sources to common outlets. 3-way valves, like the 2-way counterparts, can use actuators that improve their responsiveness and enhance precision in different industrial applications.
The multiport configurations of 3-way valves make them cost-effective alternatives to using multiple 2-way valves with complex automation. A single 3-way valve can provide directional fluid control and shut off. These valves offer reliable fluid service in heating and cooling applications, steam and boiler applications, chemical mixing processes, hydraulic and pneumatic applications. 3-way valves are also suitable for use as by-pass valves in pipe systems having primary and secondary loops.
L-Port Versus T-Port 3 Way Valves
There are different multi-port valves available in the market, ranging from 3-way ball valves, 3-way globe valves, 3-way butterfly valves and 3-way gate valves. 3-way ball valves are the most popular due to their simple design, ease of actuation and durability. The control of fluids past these valves depends on:
The pipe set up: is the pipe system horizontal or vertical?
The direction of handle rotation
Design of the port: L-port or T-port?
The subsequent discussions regarding L-port and T-port designs refer to 3-way ball valves. Valve manufacturers provide arrows on the valve handles that mimic the fluid flow paths through the control mechanism. These marks indicate flow directions.
L-Port Valves
The L-port, L-pattern valve allows the convergence of fluid from two different inlet ports without ever using the same inlet port and directs it to a common outlet. They have two inlets and one outlet port. L-port valves can provide fluid diversion service in some applications. Assume inlet ports (A and B) are horizontal, and the lower port (AB) is the outlet. The initial flow is from the inlet port (B) to the outlet (port AB).
Possible Flow Positions (A, B, C and D) In The L-Port Valve
Shifting the valve lever or the actuator through 90° clockwise changes flow direction from port A to common outlet AB.
Turning the lever through another quarter-turn moves the valve through 180°. At this point, the 3-way valve shuts off the flow of fluid past the valve. Some L-port valves can move through 360°, providing two shut-off positions. In a vertical L-port orientation, the outlet port (AB) is always in an open position.
Applications of L-port Valves
The versatility of L-port valves implies that they can provide shut-off, directional control, fluid diversion or bypass where necessary. A typical application of L-port valves (vertical or horizontal) is alternating sources of fluids in a process.
T-Port Valves
T-port valves primarily divert fluids from one source to different outlets or mix two sources to a single outline. The valves split or divide the flow of fluids into two directions. Flow enters the valves through one inlet and flows to two destinations.
T-port or mixer valves can have all three ports open at once. The T-pattern allows the service media to flow in two opposite directions or a straight-through flow. The common port is always open if the T-port valve is vertically-configured.
Possible Flow Positions (A, B, C and D) In The T-Port Valve
Turning the valve lever or actuator through a quarter-turn diverts the flow of fluids to either direction - like an L-port valve. T-port valves cannot provide an "all ports closed" configuration. Three-way valves can have lock handles that prevent the flow control mechanisms from exceeding the 90° turns, however, they can also have 180° or 360° rotation. Limiting the motion of the ball or flapper offers better control over the volumes of fluid to divert or mix within the valve body.
Applications of T-port Valves
T-port valves can provide constant fluid flow service, media mixing and sampling. They are also suitable for use as bypass valves. Some general industrial applications of T-ported valves include:
Merging fluid flow from two different sources. For instance, in a piping system in a beverage production line, the valve may serve as a primary combination point for fluids coming from a pure water line and a juice concentrate storage tank.
Diverting flow from a single source to two different destinations at once. It’s important to keep the pressures of the inlets balanced and higher than the outlet port in order to allow for a smooth mixing process
Changing flow between two storage tanks or destinations (when used like an L-port valve)
Tips For Selecting and Maintaining 3 Way Valves
There are a few guidelines that pipeline engineers and designers should consider when selecting 3-way valves for different industrial applications. Some critical tips include:
Choose the appropriate valve sizes. Undersizing the 3-way valve will increase the pumping costs of the system. Oversizing the valve reduces pumping costs but will cause control inaccuracies. Valve movements at the beginning and the end of travel will have minimal effects on the distribution of fluids past the ports.
Evaluate the physical and chemical qualities of the service fluids. If using the valve for mixing, the valve material and sealing components must be compatible with the service media. Valve materials must adhere to statutory regulations and certification standards
The pressure and temperature ratings of the 3-way valves should accommodate the flow conditions and variations of the service fluid.
Confirm the connection types of the 3-way valves to ensure they are compatible with the existing pipelines. When choosing the valves, select a connection method that will simplify the maintenance of the piping system, valves and actuators. 3-way valves having flanged connections are easier to maintain and replace than their welded counterparts.
Also, consider the actuation mechanisms. What type of actuators will meet the requirements of the piping system?
Conclusion
The multiport configurations of 3-way valves allow better flexibility and control in different industrial applications. The valves have different internal designs that give them unique performance characteristics. The capability of a single 3-way valve to handle the diverse flow applications implies that fewer valves are required. It reduces the cost of installation, operations and maintenance. If you’re unsure in your selection, make sure to consult a valve engineer at ValveMan.com to help you make the right decision.
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