Valves play a crucial role in controlling the flow of liquids, gases, and sometimes solids, despite their seemingly simple function. Acting as the equivalent of an on/off or dimmer switch for tangible substances, each valve is meticulously designed to regulate the movement of specific materials.
Industrial valves find application in a myriad of products and systems, ranging from water infrastructure to offshore oil rigs. With such diverse usage, valves come in an extensive array of shapes and sizes, spanning from straightforward designs to intricately complex ones.
Despite the vast variation, most industrial valves share common basic components: body (or enclosure), bonnet, actuator, valve member, and seat.
Valve Body
The valve body, also known as the enclosure, is typically the largest component of the valve. Material flows through the body between the ports, with all other valve components connecting to it. For instance, in a standard gate valve, there are typically three holes: the upstream port, where material flows into the body; the downstream port, where material exits the body; and another hole on top to connect the bonnet and actuator. While many valves have three or more ports, the basic configuration remains similar.
Valve bodies can vary depending on the type, size, and complexity of the valve. They may be constructed as a single piece or assembled from several separate pieces. Modern casting processes utilizing cores allow for the addition of complex inner cavities. These processes, including shell mold casting, investment casting, and permanent mold casting, are often used for casting valves.
Valve Bonnet
The valve bonnet may not be essential for every valve, but it’s a common component found in most standard industrial valves. It attaches to the top of the valve body, either through internal threads within the body or bolts connecting flanges on both the body and the bonnet. The bonnet’s internal structure allows for the attachment of additional components such as the actuator and valve member.
While the bonnet typically remains fixed during valve operation, it can be removed for servicing internal parts or clearing obstructions from the body. In some instances, the bonnet and body are combined into a single part. However, even when separate, the bonnet is often considered part of the overall enclosure. Without it, material flowing through the valve would leak, rendering the valve inoperable.
Valve Actuator
Actuators are arguably the most critical component of a valve as they enable flow control; without this capability, a valve would merely function as a conduit or container. Actuators range from simple hand wheels or handles to sophisticated computerized automated valve controllers.
In a conventional globe valve setup, the operator rotates the hand wheel situated atop the valve, prompting the actuator to move a stem up and down along a threaded channel within the bonnet. As the stem ascends, it disengages the valve member from the funnel-shaped seat, permitting material to flow through the valve body.
Valve Member
The valve member is the component directly responsible for halting the flow of material through the valve body. Its shape varies depending on the valve type. For instance, globe valves commonly employ a disc-shaped valve member with tapered sides or even a ball-shaped member that seals against a funnel-shaped seat. Ball valves, as the name suggests, feature spherical valve members cut to allow flow when the valve is open. Meanwhile, butterfly valves utilize disc-shaped members that rotate to either permit or block flow.
Valve Seat
The seat is a crucial feature of the valve body, serving as the counterpart to the valve member. When the valve is fully closed, the valve member and seat should make complete contact, creating a tight seal to prevent any material from passing through. In globe valves, the seat corresponds to the sides of the tapered, disc-shaped valve member, ensuring a seal when they come together. Similarly, in butterfly valves, the seats are integrated into the valve bodies and facilitate sealing when the valve members make full contact. In many instances, valve seats are coated with rubber or Teflon to enhance the ability to form a tight seal.
Manufacturing Industrial Valves
Valves consist of multiple parts, making it impractical to manufacture them using a single process. While metal casting is the preferred method for producing most valve components, they typically require machining to achieve the desired finish.
To ensure optimal strength and sealing capabilities, valve bodies can be cast as single parts by utilizing molds and cores. Processes such as shell molding, investment casting, and greensand casting facilitate the production of hollow parts with intricate inner cavities. Due to this capability, these three methods are commonly employed for casting valves.
After casting valve parts, the subsequent step involves utilizing CNC machining to refine the parts. Ports, through which material enters and exits the valve body, can be threaded to enable attachment to pipes on both ends. Additionally, the interface between the valve body and the valve bonnet is often threaded, facilitating connection and disconnection for maintenance purposes.
Depending on the valve mechanism, actuators may require more machining than casting. For instance, the threaded stem between the actuator and the valve member in gate valves may be entirely machined from bar stock. If valve members are not fully machined, they typically undergo some machining to ensure a precise fit. Similarly, although the basic shape of the seat may be included in the valve body casting, machining is necessary to ensure a snug fit with the valve member.
