Valves

Valve: It is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure.The simplest, and very ancient, valve is simply a freely hinged flap which drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open by flow in the opposite direction. This is called a check valve, as it prevents or “checks” the flow in one direction. Modern control valves may regulate pressure or flow downstream and operate on sophisticated automation systems.

Valves have many uses, including controlling water for irrigation, industrial uses for controlling processes, residential uses such as on / off and pressure control to dish and clothes washers and taps in the home.

Valves are quite diverse and may be classified into a number of basic types. Valves may also be classified by how they are actuated:

Hydraulic
Pneumatic
Manual
Solenoid valve
Motor

Valves vary widely in form and application. Size typically range from 0.1 mm to 60 cm. Special valves can have a diameter exceeding 5 meter.
Valves can be categorized into the following basic types:

Ball Valve: used for on/off control without pressure drop, and ideal for quick shut-off, since a 90° turn offers complete shut-off angle, compared to multiple turns required on most manual valves.
Butterfly valve: used for flow regulation in large pipe diameters.
Ceramic Disc valve, used mainly in high duty cycle applications or on abrasive fluids. Ceramic disc can also provide Class IV seat leakage
Clapper Valve: used in appliances like the Siamese fire appliance to allow only 1 hose to connected instead of two (the clapper valve blocks the other side from leaking out.
Check Valve or Non-Return Valve: allows the fluid to pass in one direction only.
Choke Valve: a valve that raises or lowers a solid cylinder which is placed around or inside another cylinder which has holes or slots. Used for high pressure drops found in oil and gas wellheads.
Control Valves: used to control fluid flow by varying the size of the flow passage
Diaphragm Valve: which controls flow by a movement of a diaphragm. Upstream pressure, downstream pressure, or an external source (e.g., pneumatic, hydraulic, etc.) can be used to change the position of the diaphragm.
Dismantling Joint: are double flanged fittings that accommodate up to 100mm (4”) longitudinal adjustment and can be locked at the required length with the tie bars supplied.
Gate Valve: mainly for on/off control, with low pressure drop.
Globe Valve: good for regulating flow.
Hydrant: is an outlet from a fluid main often consisting of an upright pipe with a valve attached from which fluid can be tapped.
Knife Valve: similar to a gate valve, but usually more compact. Often used for slurries or powders on/off control.
Needle Valve: for accurate flow control.
Pinch Valve: used for slurry flow regulation and control.
Piston Valve: used for regulating fluids that carry solids in suspension.
Plug Valve: slim valve for on/off control but with some pressure drop.
Poppet Valve: commonly used in piston engines to regulate the fuel mixture intake and exhaust.
Spool Valve: used for hydraulic control.
Thermal Expansion Valve: used in refrigeration and air conditioning systems.
Pressure Reducing Valve: used to automatically reduces a higher inlet pressure to a steady lower pressure.
Sampling Valves: used in process industries that allows taking a representative portion of a fluid
Safety Valve: used to automatically to relieve excessive pressure.
Relief Valves: used to control or limit the pressure in a system

MATERIAL OF CONSTRUCTION

D.I – Ductile Iron
C.I – Cast Iron
C.S- Carbon Steel
S.S – Stainless Steel
C.S – Cast Steel
Duplex Stainless Steel