HAEGER VALVES LLC
ANSI industrial valves

The valve body, also called the housing, is the core component of any valve. It provides the main structure of the assembly, holding all other parts together, and serves as the primary pressure boundary, designed to withstand the internal pressures of the media flowing through connected pipelines. The body links the inlet and outlet piping via threaded, flanged, bolted, or welded connections, with ends configured to match the pipeline type - such as butt weld, socket weld, threaded, or flanged. Valve bodies are typically cast or forged and shaped according to specific functional requirements, using materials suitable for the intended application.

The bonnet covers the opening in the valve body and is the second most critical part in pressure valves. Like the body, bonnets are available in a variety of designs and are usually cast or forged from the same material as the body. They are attached using threaded, bolted, or welded connections. During assembly, internal components such as the stem, plug, or wedge are inserted, and the bonnet holds them in place. The connection between the bonnet and body is considered a pressure boundary, meaning that welds or bolts attaching it are pressure-retaining elements.

The valve trim refers to the removable internal parts in contact with the flow medium, including seats, plugs, wedges, fasteners, spacers, guides, bushings, and springs. While the body, bonnet, and gaskets also contact the medium, they are not part of the trim. 

Trim design - defined by the interface between disc and seat - determines flow characteristics. In rotary motion valves, the plug or wedge moves closely past the seat, while in linear motion valves, the disc lifts perpendicularly to create an annular flow path. 

Trim components can be made from various materials depending on the forces and conditions they face, such as chemical composition, pressure, temperature, flow velocity, or viscosity. For instance, valve discs and seats are exposed to different conditions as bushings and packing glands. Flow media properties are essential factors in the selection of the trim materials. Trim may or may not match the valve body or bonnet material.

The disc controls, throttles, or stops the flow depending on its position and acts as the primary shut-off element. It is the third key pressure-retaining component, as the full system pressure acts upon it when closed. Discs are usually forged or cast and, in some cases, hard-faced (e.g., Stellite) to enhance wear resistance.

The seat or sealing rings provide the surface against which the disc rests to stop or control flow. A valve may have one or more seats: check valves usually have a single seat forming a seal with the disc, while gate valves have two - one upstream and one downstream. The gate valve disc has two contact surfaces that form the seal, halting the flow. 

To enhance durability, seating surfaces are often hard-faced with weld overlay. A smooth finish in the seat area is essential for a tight seal when the valve is closed. Seating rings themselves are generally not considered pressure-retaining components, as the valve body alone is sufficient to handle the design pressure.

The stem transmits motion to the disc, plug, wedge, or ball, opening or closing the valve and ensuring correct positioning of the shut-off element. One end connects to the handwheel or lever, and the other to the shut-off element. In gate and globe valves, linear motion is used, whereas plug, ball, and butterfly valves rotate the disc. Stems are typically forged and attached via threads or other secure methods. A smooth surface finish in the sealing area prevents leakage.