Relief and Safety Valves Relief and safety valves prevent equipment damage by relieving accidental over-pressurization of fluid systems. The main difference between a relief valve and a safety valve is the extent of opening at the setpoint pressure. A relief valve, illustrated in Figure 28, gradually opens as the inlet pressure increases above the setpoint. [...]
Stop Check Valves A stop check valve, illustrated in Figure 27, is a combination of a lift check valve and a globe valve. It has a stem which, when closed, prevents the disk from coming off the seat and provides a tight seal (similar to a globe valve). When the stem is operated to the [...]
Butterfly Check Valves Butterfly check valves have a seating arrangement similar to the seating arrangement of butterfly valves. Flow characteristics through these check valves are similar to the flow characteristics through butterfly valves. Consequently, butterfly check valves are quite frequently used in systems using butterfly valves. In addition, the construction of the butterfly check valve [...]
Piston Check Valves A piston check valve, illustrated in Figure 25, is essentially a lift check valve. It has a dashpot consisting of a piston and cylinder that provides a cushioning effect during operation. Because of the similarity in design to lift check valves, the flow characteristics through a piston check valve are essentially the [...]
Lift Check Valves A lift check valve, illustrated in Figure 24, is commonly used in piping systems in which globe valves are being used as a flow control valve. They have similar seating arrangements as globe valves. Lift check valves are suitable for installation in horizontal or vertical lines with upward flow. They are recommended [...]
Tilting Disk Check Valves The tilting disk check valve, illustrated in Figure 23, is similar to the swing check valve. Like the swing check, the tilting disk type keeps fluid resistance and turbulence low because of its straight-through design. Tilting disk check valves can be installed in horizontal lines and vertical lines having upward flow. [...]
Needle Valve Body Designs One type of body design for a needle valve is the bar stock body. Bar stock bodies are common, and, in globe types, a ball swiveling in the stem provides the necessary rotation for seating without damage. The bar stock body is illustrated in Figure 21. Needle valves are frequently used [...]
Needle Valves A needle valve, as shown in Figure 20, is used to make relatively fine adjustments in the amount of fluid flow. The distinguishing characteristic of a needle valve is the long, tapered, needle-like point on the end of the valve stem. This “needle” acts as a disk. The longer part of the needle [...]
Butterfly Valve Seat Construction Stoppage of flow is accomplished by the valve disk sealing against a seat that is on the inside diameter periphery of the valve body. Many butterfly valves have an elastomeric seat against which the disk seals. Other butterfly valves have a seal ring arrangement that uses a clamp-ring and backing-ring on [...]
Butterfly Valves A butterfly valve, illustrated in Figure 19, is a rotary motion valve that is used to stop, regulate, and start fluid flow. Butterfly valves are easily and quickly operated because a 90o rotation of the handle moves the disk from a fully closed to fully opened position. Larger butterfly valves are actuated by [...]
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