Valve, in mechanical engineering, device for controlling the flow of fluids (liquids, gases, slurries) in a pipe or other enclosure.
Different types of valves:
Different types of valves:
Globe valve: It operates by reciprocating action of disc or plug. The disc or plug moves to or away from the seat thereby stopping the fluid flow or allowing the fluid to flow. Pressure drop in the globe valve is high.
Gate valve: Gate valve functions by the reciprocating action of disc in its body. It can have a single disc or double disc. It is used for shut off operation. In double disc valve shut off is good.
Ball valve: Ball valve has a spherical plug. The spherical plug is a controlling element. They are widely used in chemical process industries. It is used where throttling and shut off combination is required. It offers good flow characteristics.
Butterfly valve: In butterfly valve the controlling element is a disc called as blade, vane or flapper, which rotates in horizontal or vertical direction and allows the fluid to flow. Butterfly valve is suitable for throttling or on-off operation at low pressure drop.
Diaphragm valve: Main parts of a diaphragm valve are, body, bonnet and a flexible diaphragm. Diaphragm is lifted up when the valve is opened and the diaphragm is tightly pressed against the bottom of valve, when it is closed.
Plug valve: Plug valve is used for on-off service. It is the oldest type of valve. The main parts of a valve are body, plug and cover. Plug can be cylindrical or tapered. The plug has a slit cut in it to allow the fluid to flow.
Needle valve: Needle valve contains a plug. The plug is tapered and sits very accurately into the seat. The flow rate is regulated by the annular space between the tapered body of the plug and the seat. It is used for small and accurate flows.
Angle valve: In angle valve the inlet and outlet ends are at 90° to each other. The axis of the stem is in line with one of the ends. Angle valve gives lower pressure drop and less pipe fittings in the piping system. Angle valves can be used for corrosive fluids.
Pinch valve: It can be used for on-off and throttling operations. The valve has a sleeve which is replaceable. It has low maintenance cost, low pressure drop and low initial cost. It can be used for handing slurries.
Slide valve: It is used for controlling low pressure flow of gases, liquids, suspensions and fluidized solids. It has two parallel body seats between which the disc slides.
Flush bottom valve: It has wide applications in process industries for discharging materials from tanks. It is available in size ranging from 25 mm to 150 mm. It can be used for discharging dry solid material from bins.
Solenoid valve: It is a control valve. Solenoid is applied to sliding stem, on-off globe valves. It is used for emergency shut off service requirements.
Control Valve: It is necessary for automatic process control system. It can be used either for controlling level, flow rate, temperature, pressure etc. The selection of control valve involves its operation mechanism, process conditions as well as requirements.
Flow regulating valve: In a flow regulating valve a constant flow rate is maintained irrespective of any changes in the line pressure. As the pressure changes on either side of the stream, the diaphragm actuates a spring loaded valve.
Back pressure regulating valve: It has a spring loaded disk or piston. The disc or piston lifts up and opens the valve whenever the pressure in the system exceeds the pressure exerted by the spring.
Check valve: It is used to prevent flow reversal. Fluid pressure keeps the valve open. It is closed either by back pressure of fluid or by weight of the check system.
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