The regulating valve is composed of an actuator valve in HVAC and a regulating mechanism. It controls the working of the valve through a signal from an external regulating device to adjust the flow through the valve. In the air conditioning system, a two-way valve is used at the terminal equipment (coil) to control the action of the actuator valve in HVAC according to the signal of the indoor thermostat or the air supply temperature, so as to push the valve stem to control the spool up and down, and to change the flow area between the valve and the valve seat to realizes the purpose of adjusting the flow rate and finally meets the requirements of users.
Due to the static pressure and dynamic pressure, when fluid flows through the valve, the valve core will get axial force from both above and below, and the combined force will cause imbalance. The magnitude of this imbalance force is connect with the structure of the valve and the channel, the size of the channel, and the position of the spool. For instance, the unbalanced force generated when a large-diameter single-seat valve approach to closing will be very large. This requires that the actuator valve in HVAC of the regulating valve must provide a large enough output force to overcome this unbalanced force, otherwise, the valve core will not be able to reach the position required by the control signal, which will lead to failure of regulation.
The regulating valve is not allowed to be in a completely closed state in some application conditions. In this way, at any time, it is necessary to ensure that the flow through the channel cannot be lower than a certain lower limit. Just as you are not allowed to burn the gas or electricity hot water devices without water, and make the inside of thewater chiller frozen, etc. This matter is related to safety that requires special attention. However, it is not very difficult to solve. You can make your requirements clear when ordering, and the supplier will set the valves up before they leaving factory.