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Time: 22th, Apr, 2014

How to selection of control valve


һ.The importance of control valve selection

The control valve is controlled actuator system, a direct response to the quality of its application in the system of regulation on quality. As a process control terminal device, the importance in it than in the past have updated knowledge. The quality of control valve applications, in addition to the quality of the product itself, the user is properly installed, use, maintenance, the correct calculation, selection is very important. Selection of calculation errors, causing the system to open to open the stop, and some can not even put into use, so for users and system designers should be aware of the importance of valves in the field, we must pay enough attention to the selection valve.

.The principle of control valve selection

1.According to the process conditions, select the appropriate structure and materials.

2.According to the technical characteristics of the object, select the control valve flow characteristics.

3.According to the process operating parameters, select the appropriate aperture size control valves.

4.According to process requirements, select the required assistive devices.

5.The reasonable selection of actuator. Response speed of the implementing agencies should be able to meet the process.

.Control valve types in the electric power industry and selection

1.The main water valve, auxiliary boiler feed water valve, water valve complex:

Control requirements: to control boiler water, the maintenance of boilers and steam flow level.

Working conditions: the boiler starts up to 100-300 kg of pressure valves, flow is small, less pressure during normal operation, traffic flow, flow adjustable ratio 75:1-100:1.

Valve requirements: body material to WCB/WC9, double valve system for the start valve requirements in anti cavitation, V level off level for the compound to the water valve, need to use the features of trim meet boiler startup and normal operation needs. General valve options for fault shutdown, (note that the general in water to remove dissolved oxygen will be added hydrazine processed, it will produce adverse reactions, SATELLITE6 No. alloy or other similar alloys it is best not to use 316 STELLITE surfacing processing valve parts, can be directly using 416 stainless steel).

2.Boiler feed pump minimum flow recirculation valve:

Control requirements: the safety of boiler feed pump start and run, to eliminate traffic flow is too small, temperature increase, water strong cavitation damage to pumps. (power switches are used to the old type, the minimum flow control valves, as well as use of mechanical pump automatic circulation valve).

Conditions: the pressure drop up to 160-350 kg, is the largest power system to withstand pressure valves, flow is generally 30% of normal flow.

Valve requirements: resistance to cavitation, attempts to prevent the structure, V sealed valve continuous work, pump start and stop running, the pump normally starts off valve after the second valve, the valve is normally open fault.

3.High / low heater water heater, water heater condensation:

Control requirements: to control the location of condensed water heater, timely condensate discharge, high water discharge, the normal water level of hydrophobicity.

Conditions: the medium is saturated water, heater control valve between the pressure is generally 6-30 kg, and finally a trap directly connected to the condenser or deaerator.

Valve requirements: Flash erosion resistance, V or VI level seal level, the valve is normally open fault.

4.Deaerator water level control valve (DALC):

Control requirements: to provide flow to maintain the normal water level of deaerator, by adding steam to increase the temperature to eliminate the gas dissolved in water.

Condition: the flow of small start-up phase, a larger pressure difference, the normal flow rate, pressure difference, similar to the valve condition.

Valve requirements: low flow cavitation effect at the time.

5.Reducing temperature valve (desuperheater):

Control requirements: the high-pressure water jet of steam into the steam temperature control requirements.

Conditions: the medium is water, a larger pressure difference, valve requirements: type diversity: nozzle type, assisted atomization type, self-contained type and the clip.

6.Temperature and pressure reduction valve (high, low pressure bypass valve):

Control requirements: the high temperature and high pressure steam steam to adjust to a certain temperature and pressure; to provide a bypass channel turbine, boiler and steam turbine capable of independent work.

Condition: the high temperature high pressure steam temperature and pressure reduction.

Valve requirements: thermal shock, noise reduction, quick response.

Selection of accessories

In the production process, the control system of the valve made every kind of special requirements, therefore, control valve must be fitted with various ancillary devices (the annex) to meet the needs of the production process. Control valves accessories include:

1.The valve positioner is used to improve the working performance of control valve characteristics, to achieve the correct positioning;

2.Valve position switch shows the upper and lower valve travel position;

3.Pneumatic valve to secure his position when the control valve of the gas supply failure, keep the valve in the gas supply failure occurs before the opening position;

4.Solenoid valve to achieve the electromagnetic switching air way, to ensure that the valve in case of a power failure in the safety valve opening position desired;

5.The hand wheel when the controller control system failure, can switch to manual operation of the valve;

6.Pneumatic actuators following the executing agency action speed, reduce the transmission time;

7.Air filter relief pressure valve for the purification of air, adjust air pressure;

8.The gas tank when the gas supply to ensure failure, so no can spring cylinder piston actuator control valve to the fail safe position. Requirements and valve size depends on the size of the cylinder, the valve action time working conditions etc.;

In short, the role of the annex is to control the valve to function better, more reasonable, more complete.

Chinabase Machinery is a group of manufacturing facilities, offering one-stop solution for mechanical power transmission products in China. We can supply a full-range of power transmission products, such as chains, sprockets and plate wheels, pulleys, gearboxes, motors, couplings, gears and racks. Our product range also covers locking assemblies (clamping elements/locking device), taper bushes, QD bushes, bolt-on hubs, torque limiters, shaft collars, motor bases and motor slides, chain detachers, chain guides, universal joint, rod ends and yokes.







Article tags: Linear Guideway,Precise Work StagePower Transmission.




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