Steps in selection of valves

valves

Presented by D.NAGABABU(GET-PP)

What is Valve?

Is a piece of mechanism ,the function of which is to check or control the flow of a fluid through a passage. Operated by pressure of the fluid or by hand or by some external mechanism. Valves can be specially made to work at high or low temperatures (cryogenic), or to very high standards for use in explosive atmospheres, or when no leakage is permissible.

functionsIsolationRegulationNon-returnSpecial purpose

Valve salient points

1. "ON/OFF": Stopping or starting flow.2. "Regulating": Varying the flow rate of flow3."Checking": Permitting flow in one direction.4."Switching": Switching flow along different routes.5. "Discharging": Discharging fluid from a system.

isolationGate valvesBall valvesPlug valves Piston valvesDiaphragm valvesButterfly valvespinch

RegulationGlobe valvesNeedle ButterflyDiaphragmPistonPinch

Non return valvesCheck valves

Special purpose MultiportFlush bottomFloatFootPressure relief Breather valves

Material of construction available Cast ironBronzeGun metalCarbon steelStainless steelAlloy carbon steelSpecial alloys

Design FeaturesInternal Sealing Systems And Materials,Body/Housing Materials, made of mild or alloy steel. Brass valves are used for water (as well as cast iron, steel and other alloys).

Stainless steel is used for acids and other corrosive liquids. Bronze is also a commonly used material which can cope with most liquids.

External Sealing Systems And Materials ,Actuation of ValvesStandards of Manufacture British Standards BS; German Standards DIN; US Standards ANSI American Petroleum Institution

Steps in selection of valvesWhat is to be handledLiquidgas or power

Consider nature of the fluidIs substantial neutral or non corrosiveTo be performed by valveOn/off , regulating for control or dosingMaterial of constructionDisc typeStem typeMeans of operating the stem operatorBonnet typeBody ends flanged ,welding etcDelivery timePrice

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Gate Valve: Used for shut off - ON/OFF function.

Ball/Plug Valves: Used for shut off - ON/OFF function

Globe Valves: Used for control of flow and shut off.

Butterfly Valves: Used for control of flow and shut off.

Relief Valves: Spring loaded to open at a given pressure, and used to protect systems from over-pressure.

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Check Valves: To allow flow in one direction only.

Fusible Link Valves/Piston Operated Valves: Quick acting and used for emergency shut off.

Twin Sea valves: Used when tight shut off required.

Semi-Needle Valves: Used in conjunction instruments to bleed off part of the flow.

Ball Check Valves: Used with gauge glasses as safety precaution

Valves are used in both domestic and industrial situations to control the flow of liquids, solids and gases.

In general, valves are used for one or more of three main purposes:

1. To control the rate of flow (throttle);

2. To shut off/permit flow (ON/OFF function);

3. To isolate systems and protect products.

Valve Actuators Manual actuators Electric motor actuators Pneumatic actuators Hydraulic Solenoid actuators

Pneumatic actuators use air pressure on either one or both sides of a diaphragm to provide the force to position the valve.

Hydraulic actuators use a pressurized liquid on one or both sides of a piston to provide the force required to position the valve.

Solenoid actuators have a magnetic slug attached to the valve stem. The force to position the valve comes from the magnetic attraction between the slug on the valve stem and the coil of the electromagnet in the valve actuator.

Ball valvePurpose: Ball and plug valves are used to provide a quick, simple shut-off.

They are operated by turning the ball or plug through 90.

Ball and plug valves should not be used for throttling, as a restriction in the flow will lead to erosion of the valve.

Gate valveare generally used in systems where low flow resistance for a fully open valve is desired and there is no need to throttle the flow.

Globe valvesused in systems where good throttling characteristics and low seat leakage are desired and a relatively high head loss in an open valve is acceptable.

Plug valvesPlug valves are often used to direct flow between several different ports through use of a single valve.

Twin-Seal ValvesPurpose: Twin-seal valves may be used when an extra tight shut-off is required.

They are basically plug valves, but have an additional action which forces sealing segments against the inlet and outlet ports providing a positive seal.

Check valves

A valve that is designed to allow the fluid to flow in a given direction but closes to prevent back flow.

Typesinclude swing check, tilting-disc check, and wafer check, non slam (piston type).

Check valves(also called non-return valves) are usually self-acting.

Lift Check Valve with Piston-Type Disc, Oblique Pattern.

Lift Check Valve with Ball-Type Disc, Standard Pattern

Swing Check Valve.

and pinch valves are used in systems where it is desirable for the entire operating mechanism to be completely isolated from the fluid. may be used for slurries

Diaphragm valves

Butterfly valvesprovide significant advantages over other valve designs in weight, space, and cost for large valve applications.

A stop check valve is a combination of a lift check valve and a globe valve and incorporates the characteristics of both.

Safety/relief valves are used to provide automatic overpressurization protection for a system.

Quick Closing Valves

Quick closing valves can be installed in pipelines and systems to isolate sections in case of fire, leakage or other emergencies.

A spring is usually used to operate the valve and can be released by a number of methods:

Fire melts fusible link;

Remote manual cable;

Air operated actuating cylinder;

Electrical solenoid, etc.

Pressure reducing valve.A self-operating valve used to reduce any excess pressure in a system, for example steam. Also known as a PRV.

The valve opens if the internal pressure exceeds that holding the closing element onto the seat

Relief ValvesPurpose: Relief valves are used to protect systems from over-pressure or to control processes by allowing flow to commence when a certain pressure has been reached.

Bypass valve.A valve smaller in diameter that is fitted in parallel to a larger main valve.

Bypass valves are used to reduce the differential pressure across the main valve

Control valve.A valve that regulates the flow or pressure of a fluid.

Control valves normally respond to signals generated by independent devices such as flow meters or temperature gauges.

Types of control valvespressure: regulate the pressure.

Direction: control direction flow of fluid to the actuator in the hydraulic circuit.

Function: Either starts or stops the flow of fluid

Cryogenic valves. Valves suited for use at temperatures below 45degrees Celsius.

A cryogenic valve should have a cold box as an integral part of the body to allow a vapour barrier to form between the packing box and the liquefied gas.

Float valve.A valve that automatically opens or closes as the level of a liquid changes.

The valve is operated mechanically by a float that rests on the top of the liquid

Manual valve.A valve that is worked by manual operation, such as a hand wheel or a lever.

These valves are generally used for on-off service.

Tank valve. A valve arranged for fitting at the bottom of a tank or process vessel.

Three-way valve. A diverter type valve that has three ports and allows the flow path of the process fluid to be switched, or two different flow paths to be combined.

Design parametersDesign pressure. The pressure used during the design of a piping system, and defines the criteria for pipe wall thickness, fittings, flanges, valves, bolt torque, and threads.

Design temperature. The temperature used during the design of a pipingsystem, and defines the criteria for pipe wall thickness, fittings, flanges,valves, bolt torque, and threads.

Operating medium. The power supply used to operate an actuator: can be pneumatic, hydraulic, or electric.Operating pressure. The pressure at which a valve usually operates under normal conditions. This is lower than the design pressure.Operating temperature. The temperature at which a valve usually operates under normal conditions. This is lower than the design temperature.

Hydrostatic test.A test using water under pressure to detect any leaks through the body, sealing joints, or closure element.

Generally this test pressure is 1.5 times the design pressure at ambient temperature

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