Industrial Control Valves: Selection Considerations and Process Integration

Industrial control valves are commonly used as operating mechanisms to direct processes in certain ways. They are found in process circuits and process integration, and are crucial components of a pipe system. A control valve can also be an important connecting unit that links every process stage. It mainly facilitates continuous flow as well as balances pressure levels. The pressure is generated ahead of or behind the valve, and is a result of the dynamics of the system components installed upstream and downstream

In designing industrial control valves, there are some crucial considerations that should not be ignored by manufacturers. These considerations include the process-technological design, the safety design and malfunction reaction, and process control concepts like communication between actuators and actuation dynamics.

In determining an effective control valve, it is important to look into its sealing function capability during controlled shutdown, an auxiliary failure or an interruption of the signal. Operators should take in consideration the leakage requirements for the closed valve and flow efficiency. Flow efficiency, which is defined by the Kv, describes the flow rate of a particular control valve. However by American standards, it is the Cv which describes the flow rate in gpm (gallons per minute) at 1 psi (pressure difference.

When deciding the right nominal size for industrial control valves, operators must identify the expected flow rate coefficient of the process system as well as the desired valve trim design. As a general rule, the nominal valve size must not exceed the normal size of the pipe where it's going to be installed. However, the valve size should not also be less than half the size of the pipe.

When the liquid or gas products that go through the flow process contain solids, they naturally require greater space. For this type of media, experienced operators usually utilize industrial control valves with an angle design to effectively facilitate the outlet flow towards the exit section of the valve. Angle-style control valves are also most suitable for fluids close to boiling point temperature and are vaporized during a decrease in pressure.

The typical integration methods of the valve to pipe network are flanged, screwed or welded connections. Among the three, flanged connection is by far the most popular, because it offers operators easy valve extraction from the circuit for repair or maintenance without disrupting the entire facility operation. Welded connections provide permanent sealing and are seen in water or steam circuits with high-pressure lines. However, such type connection is more expensive and allows limited repair opportunity.

Valve actuators are the devices responsible for positioning the valve disk in accordance to the requirements of the flow system. There are three established designs for actuators, and these are pneumatic, electric and electrohydraulic. The pneumatic actuators are considered to be most cost-effective, and offer advantages like low actuating time, consistent sealing force and safety position capability. Thus, this actuator type remains to be the top choice for process technology. However, electrical actuators for industrial control valves also provide benefits such as direct control, stability and precision. Electric actuators should come with safety features, especially if they are going to be used in high risk and hazardous areas. Electrohydraulic actuators are more expensive and elaborate to manufacture but they offer good speed, strong actuation force and stability.