Two way control valve installation

With the two-way configuration, flow through the circulation system is variable. In the three-way configurations, flow remains relatively constant through the loop which includes the pump and varies in the loop containing the coil. This works well for systems in which the supply of heat, typically a boiler, or supply of cooling, typically a chiller, requires a constant flow.

In other systems, it may be that constant flow in the coil is important, perhaps to prevent freezing. In this case the pump can be in the coil loop. Control valves typically come in three valve styles: globe, butterfly, and ball. The globe-type valve has been the most common for many years, but the characterized ball valves are becoming very popular and are starting to become a significant part of the working marketplace.

Below 2-inch size, they have usually sweat soldered or screwed connections, while above 2 inch they are typically flanged.

Figure 2 shows a typical globe-type two-way single-seated control valve. It consists of a body, a single seat, and a plug. The plug is connected to a stem, which, in turn, is connected to the actuator, also called the actuator or motor. Moving the stem up and down controls the flow. Full shut-off is achieved when the plug is firmly down against the seat. Figure 2. The body is connected to the piping system in any suitable way screwed, flanged, welded, soldered, etc.

Make sure the flow direction is correct with the arrow on the valve body. Service manual valves should be provided to isolate individual control valves or piping subsystems.

An actuator that is sprung to lift the valve stem upon power loss combined with the globe valve shown in Figure 2 would produce a normally open valve assembly. The valve is open when power is removed from the actuator. Figure 3 shows a globe valve that closes with the stem up.

Using this actuator with the valve in Figure would produce a normally closed valve assembly as the valve is closed when power is removed from the actuator. In both cases, the stem must be driven against the flow of fluid to close the valve.

Figure 3. Normally Closed Globe Two-way Valve. The figures indicate that flow through the valve must occur in the direction shown by the arrow. All control valves will have an arrow cast into the outside of the body to indicate flow direction. The reason for this is as follows: in any linkage between motor and valve stem there will be some slack, a little free movement of the valve stem.

When flow occurs in the correct direction, the velocity pressure of the fluid and the fluid differential pressure across the valve will tend to open the valve. Therefore, the motor must press tightly to close it, taking up any free movement. If flow takes place in the wrong direction, the velocity pressure tends to close the valve pushing down on top of the plug of the valve in Figure 2.

When the valve throttles toward its closed position, the pressure may be enough to push the plug to the closed position, taking advantage of the free movement or slack in the valve stem.

When this happens, flow ceases, then the velocity pressure component disappears, and free movement allows the valve to crack open. Flow begins, the velocity component reappears, and the cycle is repeated indefinitely. Each time the flow stops and starts, the inertial force of the fluid in the pipe causes a shock known as water hammer.

Besides being noisy and annoying, it can cause failure of the piping system. Therefore, it is important never to install a control valve backward. Figure 4 shows a double-seated valve, also called a balanced valve. As the name implies, it has two plugs and seats arranged so that fluid differential pressure is balanced and the actuator does not have to fight against differential pressure to close the valve, as it does in the single-seated valves shown in the Figure 2.

This reduces the size of the actuator. But the valve inherently cannot provide tight shut-off. This reduces its applicability to HVAC systems, where tight shut-off is usually desired, to minimize energy costs to prevent leakage and simultaneous heating and cooling. Figure 4. Double-seated Two-way Globe Valve. Modulating globe-type control valves is made with two basic types of plugs: the linear V-port plug see Figure 5 and equal percentage plug see Figure 6.

Many manufacturers have variations on these two designs called modified linear or modified equal percentage , the characteristics of which are usually similar to those described here. Open the valve, the chilled or hot water enters the fan coil to supply air or heat to the room.

When the room temperature reaches the set value of the thermostat, the thermostat turns off the power of the electric two-way valve and the reset spring closes the valve Thus cut off the water flow into the fan coil, through the valve closed and opened, so that the room temperature is always maintained in the temperature range set by the temperature control. The drive and valve of the electric two-way valve are threaded to allow installation of the drive after the valve is installed.

Field assembly, flexible and convenient wiring. The planar design of the driver can be installed close to the wall, take up little space, the product is reliable and durable, the working noise is low, and it can work reliably in the high temperature and high humidity environment in the hidden fan coil unit.

Before installation, read the instruction manual carefully, cut off the power supply and install it by professional and technical personnel. The valve body shall be located above the coil pan to ensure that dripping occurs when falling into the pan.

Make sure to watch this short easy to understand video on control signals. Other Posts You might like. Vykon by Tridium: Get Ready! Niagara 4. Contemporary Controls July, Newsletter. Share this: Twitter Facebook LinkedIn. Share on facebook Facebook. Share on twitter Twitter. Share on linkedin LinkedIn. Share on pinterest Pinterest. Thank you! Very nice write-up.