June 2017 Blog

ATC Valves 101
Automatic Temperature Control (ATC) Valves are commonly used in the HVAC industry to maintain a set temperature through the coil of a heating or cooling system. There are three different types of ATC valves, On/Off, Floating, and Modulating, all having different levels of accuracy. All ATC valves have a sensor receiving a temperature signal that will regulate the amount of flow through the valve. The flow is typically controlled by an electric signal or mechanically with hydraulics. Electrically there are two types of devices that receive a signal, rotary actuators, or linear actuators. Rotary actuators typically control butterfly, ball, and plug type valves. Linear actuators typically control globe and diaphragm type valves. With hydraulics, a pressurized fluid determines the position of the valve, these are normally globe and diaphragm type valves. The type of system and control neededĀ  typically determines the type of ATC valve selected.
On/Off ATC valves are typically controlled electronically. There are two set points the valve will operate under, fully open or fully closed. The sensor will detect a difference in the set temperature and the actual temperature and tell the actuator to open. When the set temperature is reached the valve receives a signal from the sensor telling the valve to close. To prevent the valve from constantly opening and closing there is usually a range the actual temperature can be at (above or below) before a signal will be sent to open or close the valve. On/Off ATC valves are often referred to as 2-position Normally Open (NO) or Normally Closed (NC) valves.
Floating ATC valves have more control compared to On/Off ATC valves. Floating ATC valves are controlled electronically but have the ability to open/close slowly, and stay at a point between open and closed. When there is a difference between the set temperature and the actual temperature, a signal from a sensor is sent to the valve controller. The signal received by the controller will determine the valve position. When the set temperature is reached the valve will hold that position. This provides the system with better control of temperature through the coil.
Modulating ATC valves have the most control of temperature through the coil. Modulating ATC valves can either be controlled electrically or mechanically. The temperature differential will be continuously monitored by the sensor. The sensor will give instant feedback to the valve controller to determine its position. Electric Modulating ATC valves typically use a high-resolution controller so the valve can move and be held at any position. For mechanicalĀ  Modulating ATC valves, a hydraulic fluid is calibrated to expand or contrast depending on temperature change. This type of controller is used where the system needs to control the flow precisely to regulate the change in temperature across the coil.
The other aspect to decide on Actuators is their mode of operation during the loss of power, Spring Return type versus Non-Spring return type. For protection for the pump and maintenance of the system, ATC valves have a mechanism to keep the valve either to fully open or closed when power is removed from the valve. These valves are referred to as Spring Return ATC valves. The spring will move the actuator fully open or fully closed when there is no power. Depending on the system this option can help keep the heating/cooling fluid from back flowing to the pump, and help ease of maintenance when working on the system. As opposed to the, Non-Spring Return type actuators would normally stay in their last position during power failure.

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