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The classification of valve(1) [2009-04-07]

Although many different types of valves are used to control the flow of fluids, the basic valve types can be divided into two general groups: stop valves and check valves. Besides the basic types of valves, many special valves, which cannot really be classified as either stop valves or check valves, are found in the engineering spaces. Many of these valves serve to control the pressure of fluids and are known as pressure-control valves. Other valves are identified by names that indicate their general function, such as thermostatic recirculating valves.

Stop Valves :Stop valves are used to shut off or, in some cases, partially shut off the flow of fluid. Stop valves are controlled by the movement of the valve stem. Stop valves can be divided into four general categories: globe, gate, butterfly, and ball valves. Plug valves and needle valves may also be considered stop valves.

GLOBE VALVES: Globe valves are probably the most common valves in existence. The globe valve is named after its shape. Its body has an interior partition, and the valve inlet and outlet centers are inline. This configuration forces a change in the direction of flow in the form of an S. A Globe valve is a device for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body. Generally speaking, there are 3 styles of globe valves: straight pattern, angle pattern and Y-pattern. These are determined by the geometry of the end connection and the stem. In a straight pattern globe, the end connections for a straight line with the stem pointing vertically from this line. A Y-pattern is similar but the stem is angled by 45 degrees from the inlet-outlet path. An angle valve has the inlet and outlet oriented 90 degrees from each other with the stem perpendicular from one and in line with the other. Globe valves are used extensively throughout the engineering plant and other parts of the ship in a variety of systems

GATE VALVES: A Gate Valve, or Sluice Valve, as it is sometimes known, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar. The gate faces can form a wedge shape or they can be parallel. Gate valves are sometimes used for regulating flow, but many are not suited for that purpose, having been designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss. Gate valves are characterised as having either a rising or a nonrising stem. Rising stems provide a visual indication of valve position. Nonrising stems are used where vertical space is limited or underground

BUTTERFLY VALVES: A butterfly valve is a type of flow control device, typically used to regulate a fluid flowing through a section of pipe. The butterfly valve has a body, a resilient seat, a butterfly disk, a stem, packing, a notched positioning plate, and a handle. The resilient seat is under compression when it is mounted in the valve body, thus making a seal around the periphery of the disk and both upper and lower points where the stem passes through the seat. Packing is provided to form a positive seal around the stem for added protection in case the seal formed by the seat should become damaged. There are different kinds of butterfly valves, each adapted for different pressures and different usage. The resilient butterfly valve, which uses the flexibility of rubber, has the lowest pressure rating. The high performance butterfly valve, used in slightly higher-pressure systems, features a slight offset in the way the disc is positioned, which increases the valve's sealing ability and decreases its tendency to wear. The valve best suited for high-pressure systems is the tricentric butterfly valve, which makes use of a metal seat, and is therefore able to withstand a greater amount of pressure.For more information,please visit