Control valves are components of a pump station that control certain conditions like pressure, flow, liquid level and temperature by partially or fully closing or opening as a reaction to signals sent by the controllers comparing the set point and the variable process. This information is provided by the sensors monitoring the changes that may occur in such conditions.
The opening and closing of the control valve happens automatically with the use of hydraulic, electrical or pneumatic actuators. The opening and closing of actuators is also done by the positioners based on pneumatic or electric signals. The control signals are usually based on 3 to 5 psi. At present, the common signals used are 4 to 10 mA for the irrigation industry and 0 to 10V for the HVAC systems. In protocols, the most commonly used are the smart systems which include the Fieldbus Foundation, HART and Profibus.
The control valve is usually installed at the highest horizontal line of the piping. It should be placed in accessible location. An arrow should also be placed in the valve body to indicate the direction of the flow of water. Control valve could be installed at any position, however, upright position is recommended for easy access and maintenance.
The control system is where the feedback controls are located. You can find here several devices that will provide the system feedback during the operation. The sensors will help in gauging while the process is ongoing.
When the predetermined set point for system pressure is exceeded, the sensor will then trigger a certain mechanism so that the excess pressure will be diffused. In the same manner, the control valve is also triggered by another device to make sure that the control loop system is working properly.
Pressure Relief Valves - The valves are placed to maintain as well as control the pressure in liquid systems. A pressure level is usually predetermined and fluid is effectively relieved by the valve when pressure goes up above the set level by means of an additional passageway.
The passageway, also called the auxiliary passage will be forced to open once the pressure arrives at the set level, which means the pressure relief valve will self-deactivate.
The pressurized liquid will then be removed, converted to gas then released. The pressure relief valve is very essential for high pressure systems since it protects the components of the system from possible damage which may occur once the level of pressure exceeds the predetermined level.
Globe Valves - The valve is normally utilized to control the flow in the pipeline along with other liquid systems.
The globe valve has a circular shaped body feature and a moveable disc that can slide in and out from the fixed ring seat in order to open and close the control valve.
Butterfly Valves - These valves are basically utilized as basic on and off valves. These valves could be concentric, which means the plug and disc is aligned on the valve center; or eccentric, which means the disc of the plug is off beam.
Eccentric butterfly valves are ideal for application that requires throttling, whereas concentric butterfly valves are much more suitable for basic on and off applications.
The eccentric valves in automated butterfly valves are recommended because the plug of off-center often limits the contact between the seat and the plug that is helpful in preventing wear.