Selecting awrongly sized or incorrectly sized control valve can result to serious consequences for safety, operation, and productivity. Below is a list of some of the things you should keep in mind while selecting your control valve:
· The control valve is not an isolation valve and should not be used to isolate.
· At all times, choose the right building materials carefully. Consider valve parts that touch the process media, like valve bodies, seats, and other "wet" parts. Think through the operating temperature and operating pressure that the control valve can see. Lastly, study the ambient environment and the corrosion that may occur outside the valve.
· Place the flow sensor upstream of the control valve. Placing it downstream of the control valve makes it exposed to an unstable flow rate due to instability in the valve hole.
· Ensure that the valve can function mechanically, taking into account the degree of control required. Too many dead bands make hunting and control difficult. The dead zone is approximatelydescribed as the sum of control signal necessary to cause a change in the position of the valve. Shabby or slackly installed mechanical connection or controller adjustment causes it. In addition, tolerances of mechanical sensors, intrinsic friction of the valve stem and seat, or small actuators can affect it.
· Consider penance. The propensity for valves that have moved very limitedly or that do not move is called a "stick." This is usually caused by valves that maintain pressure on the packing glands, seats or discs. Additional forces must be applied to the actuator to overcome friction, which can result in overshoot and poor control.The EVAP system stops fuel vapors in the tank of fuel from escaping into the environment.
· Adjust the loop controller correctly. Overshoot, undershoot, and hunting will occur if the tuning is not poor. Verify that the proportional, integral, and derivative values are defined). Today, it is very easy to use a controller with advanced auto-tuning capability that supersedes the previous trial-and-error loop adjustment method.
· Do not overuse the control valve. Control valves are often larger than those required for the flow loop theyswitch. In a case where the control valve is extremely large, just a little percentage of the displacement is used (a small change in valve position will hunt the valve because it has a large effect on the flow rate). Excessive wear occurs. Always resize the control valve at about 70% -90% of travel.
· Consider the kind of control valve in use and the integral flow features. Other types of valves and their disks have various flow features (or profiles). The flow physiognomies can be by and large regarded as a change in flow rate with respect to the change in the position of the valve
Above are some of the most important criteria to consider when choosing a control valve. You should always consult a qualified professional before final selection.