The control valve regulates the rate of fluid flow as the position of the valve plug or disk is changed by force from the actuator. In order to do this, the valve should achieve various things. It should contain the fluid without external leakage. It should have adequate capacity for the intended service. Besides, it should also incorporate appropriate end connections to mate with adjacent pipelines and actuator attachment means to permit transmission of actuator thrust to the valve plug stem or rotary shaft.
With the development of technologies, there are many styles of control valve bodies. Some of them can be applied to meet various requirements. Following are introductions about some ones. van điều khiển khí nén
The first one is the single-port valve bodies. It is the most common style and is simple in construction. It is available in various forms, such as globe, angle, bar stock, forged, and split constructions. Generally, single-port valves are specified for applications with stringent shutoff requirements. They use metal-to-metal seating surfaces or soft-seating with PTFE or other composition materials forming the seal. They can handle most service requirements. Because high-pressure fluid is normally loading the entire area of the port, the unbalance force created must be considered in selecting actuators for them.
Balanced-plug cage-style valve body is also a popular type. It is single ported in the sense that only one seat ring is used, provides the advantages of a balanced valve plug often associated only with double-ported ones. Cage-style trim provides valve plug guiding, seat ring retention, and flow characterization. In addition to a sliding piston ring-type seal between the upper portion of the valve plug and the wall of the cage cylinder virtually eliminates leakage of the upstream high pressure fluid into the lower pressure downstream system.
The third one is the high capacity, cage-guided valve bodies. It is mainly designed for noise applications such as high pressure gas reducing stations where sonic gas velocities are often encountered at the outlet of conventional valve bodies. The design incorporates oversize end connections with a streamlined flow path and the ease of trim maintenance inherent with cage-style constructions.
Port-guided single-port valve bodies are also very popular. They are typically provided with screwed in seat rings which might be difficult to remove after use. Reduced dynamic forces acting on plug might permit choosing a smaller actuator than would be necessary for a single-ported one with similar capacity. There are still many other types of control valve bodies. All of them have special functions. They can meet different requirements.