The importance of type selection of control valves

Release time:2017-10-19 author:admin Browsing volume:128

The regulating valve is an actuator in the automatic control system, and its application quality is directly reflected in the system's regulating quality. As a terminal element in process control, the importance of it has been updated in the past. In addition to the quality of the product, the correct installation, use and maintenance of the user, the correct calculation and selection of the valve is very important. Due to the failure of calculation and selection, the system will start and stop, and some can not even be put into use. Therefore, for users and system designers, we should recognize the importance of valves in the field, and we must pay enough attention to the selection of control valves.

The principle of type selection of control valve

1, according to the technological conditions, select the appropriate structure and material.

2. According to the characteristics of the process object, the flow characteristics of the control valve are selected.

3. According to the operating parameters of the process, the suitable size of the control valve is selected.

4. According to the requirements of the process, the necessary auxiliary devices are selected.

5, the rational choice of the executive agency. The response speed of the actuator should be able to meet the process

Type and type selection of control valve in electric power industry

1, water supply valve main, auxiliary boiler feed water valve, compound feed water regulating valve:

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

Working condition: when the boiler starts, the pressure difference of the valve can reach 100-300 kilograms, and the flow rate is small. The pressure difference is small when normal operation, the flow rate is large, and the flow rate can be adjusted to 75:1-100:1.

Valve requirements: valve body material is WCB/WC9, for double valve system startup valve, it is required to resist cavitation and grade V shutdown. For composite water supply valve, characteristic valve internals are required to meet boiler start-up and normal operation needs. General valve options for fault shutdown, (note that the general water to remove dissolved oxygen will be handled by adding hydrazine, it will produce adverse reactions to SATELLITE6 alloy or other similar alloys so it is best not to use 316 STELLITE surfacing processing valve parts, can be directly using 416 stainless steel).

2, the minimum flow rate circulation valve of the boiler feed water pump:

Control requirements: to make the boiler feed water pump start and run safely and eliminate the damage of the pump because of the low flow rate, the increase of temperature rise and the strong cavitation of water. (the old power station has the use of a switch type minimum flow control valve and a mechanical pump automatic circulation valve).

Working conditions: the pressure drop is 160-350 kilograms, which is the maximum pressure differential valve in the power station system, and the flow rate is generally 30% of the normal flow.

Valve requirements: anti cavitation, anti blocking structure, V grade seal. When the pump starts and stops, the valve works continuously. After the pump starts normally, the secondary valve closes the valve, and the valve usually fails.

3. The water heater of the high / low heater water heater is hydrophobic and condensate water heater is hydrophobic.

Control requirements: control the location of condensate in the heater, discharge condensed water in time, that is, high water level discharge, and normal water level is hydrophobic.

Conditions: the medium is saturated with water, the pressure difference between the control valves between the heaters is generally 6-30 kg, and the last stage trap directly connects the condenser or deaerator.

Valve requirements: anti flash scour, V or VI grade seal grade, valve usually failure.

4, deaerator water level control valve (DALC):

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

Working condition: the start stage flow is small, the pressure difference is big, the normal flow is large, the pressure difference is small, the working condition is similar to the water supply valve.

Valve requirements: effective resistance to cavitation at low flow rate.

5, reducing temperature valve (temperature reducer):

Control requirements: the high pressure water is injected into the steam to make the steam temperature reach the control requirement.

Condition: the medium is water, the pressure difference is big, the valve requirement: the type variety: the nozzle type, the auxiliary atomization type, the self containment type and the clamp type.

6, reducing temperature and pressure relief valve (high and low pressure bypass valve):

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

Working conditions: temperature and pressure reduction of high temperature and high pressure steam.

Valve requirements: heat shock, noise reduction, rapid reaction.

The regulating valve is an actuator in the automatic control system, and its application quality is directly reflected in the system's regulating quality. As a terminal element in process control, the importance of it has been updated in the past. In addition to the quality of the product, the correct installation, use and maintenance of the user, the correct calculation and selection of the valve is very important. Due to the failure of calculation and selection, the system will start and stop, and some can not even be put into use. Therefore, for users and system designers, we should recognize the importance of valves in the field, and we must pay enough attention to the selection of control valves.

The principle of type selection of control valve

1, according to the technological conditions, select the appropriate structure and material.

2. According to the characteristics of the process object, the flow characteristics of the control valve are selected.

3. According to the operating parameters of the process, the suitable size of the control valve is selected.

4. According to the requirements of the process, the necessary auxiliary devices are selected.

5, the rational choice of the executive agency. The response speed of the actuator should be able to meet the process

Type and type selection of control valve in electric power industry

1, water supply valve main, auxiliary boiler feed water valve, compound feed water regulating valve:

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

Working condition: when the boiler starts, the pressure difference of the valve can reach 100-300 kilograms, and the flow rate is small. The pressure difference is small when normal operation, the flow rate is large, and the flow rate can be adjusted to 75:1-100:1.

Valve requirements: the body material is WCB/WC9, for the start valve in the dual valve system


Related labels: