Valves

What is valve?

           A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passage ways.

Valves function? 

     a. Stopping and starting fluid flow.

     b. Varying the amount of fluid flow.

     c. Controlling the direction of fluid flow.

     d. Regulating downstream system or process       

    e. pressure Relieving component or piping over pressure.

Types of valves?

•      Globe valve

•      Gate valve

•      Ball valve

•      Needle valve

•      Butterfly valve

•      Diaphragm valve

•      Check valve

•      Safety valve

•      Plug Valve

•      Control Valve

Gate Valve:

•      A gate valve can be defined as a type of valve that used a gate or wedge type disk and the disk moves perpendicular to flow to start or stop the fluid flow in piping. Gate valves operates slowly.  It is most common type of valve for fully opening or closing.

•       Minor pressure loss when fully opened.

•       It can not be used as control valve. Always it is fully opened or fully closed.

•      A gate valve is the most common type of valve used in any process plant.  In service, these valves are either in a fully open or fully closed position.

•      When the gate valve is fully open, the disk of a gate valve is completely removed from the flow. Therefore virtually no resistance to flow. Due to this very little pressure drops when fluid passes through a gate valve.

•      To achieve proper sealing, when the valve is fully closed, 360° surface contact is required between disk and seats.

•      Gate valves should not be used for regulation or throttling of flow because accurate control is not possible.

•      The high velocity of the flow in the partially open valve may cause erosion of the disc and seating surfaces and also creates vibration and noise.

•      In fully open conditions, the flow area is equal to the area of the pipe and hence, there is negligible pressure drop across the valve.

• Gate valve is a sliding type of valve
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Globe Valve:

•      A globe valve, different from ball valve, is a type of valve used for stop, Start and regulate the flow in a pipeline, consisting of a movable plug or disc element and a stationary ring seat in a generally spherical body.

•      A Globe valve is a linear motion valve and are primarily designed to stop, start and regulate flow.

•       The flow pattern through a globe valve involves changes in direction, resulting in greater resistance to flow, causing high pressure drop.

•       The globe valve is an excellent valve to use for on-off services.

•      To achieve proper sealing, when the valve is fully closed, 360° surface contact is required between disk and seats.

•      The high velocity of the flow in the partially open valve may cause erosion of the disc and seating surfaces and also creates vibration and noise.

Ball Valve:

•      It is a rotary motion quarter-turn valve.

Advantages :--

•      Maintains and regulates high volume, high pressure, and high temperature flow.

•      No lubrication requirements.

•        Can handle fluids with suspended solids.

Disadvantages :--

• Have relatively poor throttling characteristics.

• Difficult to clean, leads to contamination.

•      A ball valve is a rotational motion valve that uses a ball-shaped disk to stop or start fluid flow.

Needle Valve:

•      A needle valve is a type of valve having a small port and a threaded, needle-shaped plunger.

•      Needle valves are usually used in flow-metering applications, especially when a constant, calibrated, low flow rate must be maintained for some time.

Butterfly Valve:

•      Butterfly valve is a simple system which has a rotating thin disc rotating across the flow.

•      Quick opening valve.

•      Pressure drop across a butterfly valve is small.

•      Used with chemical or corrosive media.

•      A butterfly valve can be operated manually and automatically.

•      The effect on the fluid by the closing and opening of the disc is shown.

Diaphragm Valve:

Plug Valve:

•      It is a quarter-turn rotary motion valve.

•      The disk is a solid plug with a bored.

•      It is used as On-off stop valves.

•      It is capable of providing bubble tight shutoff. i.e sealing ability of a valve.

It can be used for high pressure and vacuum

          

Check Valve and its Symbol:

•      The check valves are non-return valves.

•      These valves allow the fluid to flow only in one direction.

•      Check valve will be open only when the fluid is flowing in the allowed direction.

•      If the fluid flows in the opposite direction, the pressure in the opposite direction closes the valve automatically.

•      These valves are important for preventing backflow to systems.

Safety Valve:

•      Safety valve is also called a pressure relief valve (PRV).

•      It automatically releases a substance/Steam/gas from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds to reference value/limits.

•      The primary purpose of a safety valve is the protection of life, property and environment.

•      A safety valve is not a process valve or pressure regulator and should not be misused as such.

•      It should have to operate for one purpose only: overpressure protection.