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An angle valve is essentially a globe valve within which the flow makes a 90-degree turn. It’s a linear motion valve designed primarily to stop, start and regulate pressure. They contain a disk capable of completely closing the flowpath or being totally removed from the flowpath altogether.
Angle valves are also designed with a stem that can move up or down to regulate the flow within the valve. They provide for a 90-degree change in flow direction, eliminating the use of extra fittings and elbows.
Ball valves are quarter-turn rotational motion valves that use a ball-shaped control element to stop or start flow. Ball valves are manufactured in different configurations, most commonly floating ball and trunnion-mounted ball valves.
Butterfly valves are quarter-turn rotational motion valves that use a round disk control element to stop or start flow. Common butterfly valve body types include wafer, lug and flanged-end designs.
Check valves are self-operated valves that open with forward flow and close with reverse flow. The pressure of the fluid passing through a system opens the valve, while any reversal of flow will close the valve. Exact operation will vary depending on the type of check valve mechanism.
Gate valves are primarily designed to start or stop flow. In service, these valves are generally either fully open or fully closed. They are available with different disks or wedges, including: solid wedges, flexible wedges and split wedges (self-adjusting and self-aligning to both seats’ sides).
Plug valves are quarter-turn rotational motion valves that use a tapered plug to stop or start flow. They typically have a rectangular port shape and come in either non-lubricated (also called self-lubricated) or lubricated designs. Plug valves can be used in many types of fluid services and perform well in slurry applications.
A pneumatic actuator mainly consists of a piston or a diaphragm which develops the motive power. It keeps the air in the upper portion of the cylinder, allowing air pressure to force the diaphragm or piston to move the valve stem or rotate the valve control element.
Valves require little pressure to operate and usually double or triple the input force. The larger the size of the piston, the larger the output pressure can be. Having a larger piston can also be good if air supply is low, allowing the same forces with less input. These pressures are large enough to crush objects in the pipe. On 100 kPa input, you could lift a small car (upwards of 1,000 lbs) easily, and this is only a basic, small pneumatic valve. However, the resulting forces required of the stem would be too great and cause the valve stem to fail.
This pressure is transferred to the valve stem, which is connected to either the valve plug (see plug valve), butterfly valve, etc. Larger forces are required in high-pressure or high-flow pipelines to allow the valve to overcome these forces, and move the valve’s moving parts to control the material flowing inside.
The valve’s input is the "control signal." This can come from a variety of measuring devices, and each different pressure is a different set point for a valve. A typical standard signal is 20–100 kPa. For example, a valve could be controlling the pressure in a vessel which has a constant out-flow, and a varied in-flow (varied by the actuator and valve).
A pressure transmitter will monitor the pressure in the vessel and transmit a signal from 20–100kPa. A reading of 3320 kPa means there is no pressure; 100 kPa means there is full range pressure (can be varied by the transmitter's calibration points). As the pressure rises in the vessel, the output of the transmitter rises. This increase in pressure is sent to the valve, which causes the valve to stroke downward and start closing the valve, decreasing flow into the vessel and reducing the pressure in the vessel as excess pressure is evacuated through the out flow. This is called a direct acting process.
Although they’re named for their spherical body shape, globe valves can often look very similar to check valves from the outside. Globe valves are linear motion valves and are generally used to control flow. Because these valves are primarily designed to stop, start and regulate flow, they contain a disk capable of completely closing the flow path or being totally removed from the flow path altogether. They’re also designed with a stem that can move up or down to regulate the flow within the valve.
Conventional globe valves may be used for isolation, throttling and pressure-reducing services. These valves commonly come in three primary body designs: tee pattern or z-body, wye pattern or y-body and angle pattern.
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