There are a number of ways for HVAC specialists to control water flow within a closed water system, and a control valve hookup is one of the most effective ways of ensuring that pressure and flow rates are appropriate within the system. Together with automatic and manual balancing valves, control valves help keep water conditions (like pressure and temperature) at the levels specified for that system for optimum performance.
Though “control valve” is the most common term, people who talk about this type of valve are actually often referring to an entire control valve assembly. Control valve suppliers may offer these parts separately or as part of an entire system.
- The valve body
- Internal trim parts
- An actuator (which powers the valve in order for it to be able to open)
- The positioner
- Supply pressure regulators
- Air sets
- Other accessories and parts
The Control Loop
A control valve must operate on a closed system loop in order to effectively maintain water pressure and flow within the system. In a closed loop, all components of the system (including the control valve assembly, sensors, pumps, transmission devices, and the vessel under pressure that is being controlled) are interconnected to allow for continuous feedback of information about the status of the water in the system. This status – known as the process variable – must be carefully monitored in order to be sure that the water within the system reaches the correct temperature (called the set point).
Correct hookup of the control loop allows information to be constantly read by the system’s sensors, and this allows for the system to make automatic adjustments to water pressure, flow, and other variables in order to achieve the right temperature.