Valve Types and Applications–IV
The globe valve is named for its spherical valve body. The spherical valve body was once very common and also named for its use of a spherical valve disc. The spherical valve disc restricts the flow by closing the restriction hole. The valve flap on the manually operated valve is opened and closed by the hand wheel, and the valve flap on the automatic valve is opened and closed by the actuator and the sliding shaft. The main specifications include valve type, port configuration, port connection, valve size, and the materials that make up the valve body, such as valve seats, seals, linings and stem packing.
The stop valves are used for closing and regulating, for example, in wastewater treatment plants, food processing plants and processing plants. The most common type is the Z-type valve, which is called the Z-type valve because of the path of the fluid through the valve body. These two right-angle rotations that the fluid must pass through are responsible for the relatively high head loss of this design. The less restrictive design is the Y-type valve, which makes the stem and the valve body at a 45° angle. The other type is the angle valve, which rotates the flow by 90°.
The shape of the valve disc can be changed to produce a valve that can quickly reach full flow, or, by using a more tapered valve plug design, to produce a valve that can accurately adjust the flow.
The stop valve can seal the fluid flow or seal together with the fluid flow according to the installation requirements (i.e. fault closed and fault open). The main function of the selection is to determine the size of the actuator. Like gate valves, shut-off valves can be of rising stem or NRS type.
Needle valves are used to measure fluid flow through pipes or ports. The flow is adjusted by inserting or pulling a tapered valve stem into or out of a similar tapered orifice, creating a very precise way to adjust the fluid flow through the orifice. The main specifications include valve type, port connection, valve size, and the materials that make up the valve body, including valve seats, seals, linings and stem packing. Needle valves are used in vacuum systems and metering systems that require precise flow adjustment. Due to the large number of turns required to close the needle valve, they are not suitable for shutting down service applications.