How to choose control valve（three）？

Valves are used for a wide variety of applications, including ball valves, ball valves for steam, butterfly valves, check valves, forged steel valves. Each valve has its own important role. Regulating valve is one of the industrial process control instruments widely used by industrial enterprises such as petroleum, chemical industry and electric power.

 

 

Selection of Accessories for Regulating Valve

1. Applicable Occasions of Valve Positioner

(1) It is used to overcome the friction or to improve the action speed of the regulating valve.

(2) When split-range control and regulating valve need to change the gas on and off.

(3) Where the flow characteristics need to be changed.

(4) When the proportional band of the regulator is very wide, but the valve is required to respond to small signal.

(5) No spring actuator or piston actuator to achieve proportional action.

(6) Use standard signal to operate the actuator of non-standard spring (spring range beyond 20 ~ 100KPA).

 

2. Applicable Occasions of Pneumatic Relay

(1) When the response speed of the regulating valve needs to be improved in the fast process, and the distance between the regulating valve and the regulator is greater than 100m.

(2) Where the output signal of the pneumatic regulator needs to be improved.

 

3. Solenoid Valve

(1) It is suitable for remote control, program control, interlock system, realizing automatic closing of the gas circuit, opening or closing of regulating valve. Straight through solenoid valve is used for double position adjustment and remote control. According to the logic relationship of program control, "normally closed" or "normally open" solenoid valve can be selected.

(2) When a large capacity is required to shorten the operating time, use a solenoid valve as a pilot valve in combination with a large capacity pneumatic relay.

(3) Explosion proof solenoid valve, intrinsic safety solenoid valve or switch type electrical converter shall be selected in the explosion hazardous area.

 

4. Position Keeping Valve

It is suitable for the occasions when the pressure of the gas source is lower than the given value and the regulating valve is required to be kept at a certain position.

 

5. Electrical Converter

(1) The control system uses electric instruments and pneumatic control valves.

(2) Turn electrical signals into gas signals.

(3) For the rapid regulation system, the electrical converter should be selected.

 

 

Installation of Regulating Valve

1. General Requirements

(1) The regulating valve should be installed vertically on the horizontal pipeline. For the regulating valve with nominal diameter DN ≥ 80mm, the front and rear pipes of the valve shall be equipped with permanent supports.

(2) The installation position of the regulating valve should be convenient for operation and maintenance. The platform should be set up if necessary.

(3)The piping of the regulating valve group should be compact to facilitate operation, maintenance and drainage.

(4)Sufficient space shall be reserved for the upper and lower parts of the regulating valve to remove the actuator, valve trim, and the lower flange and plug of the valve during maintenance.

(5)When the regulating valve is used for high viscosity, easy crystallization, easy vaporization and low-temperature fluid, measures of heat preservation and antifreeze shall be taken.

(6)The use temperature of the regulating valve is generally not higher than 60 °C and not lower than -40 °C.

(7)When the valve is installed in a place with vibration, anti-vibration measures should be considered.

(8)For the regulating valve without a valve positioner, a small pressure gauge indicating control signal shall be installed on the diaphragm head.

(9)When the regulating valve is used for the fluid with suspended solids and high viscosity, it shall be equipped with flushing pipeline.

(10)When installing the regulating valve, pay attention to make the medium flow in the direction of the calibration arrow of the valve body.

 

2. Precautions for Installation of Self Operated Regulating Valve

For the pressure-type pressure regulating valve, filter shall be installed in front of the valve. The distance between the pressure tapping point and the regulating valve shall not be less than 10 times of the pipe diameter. When the temperature regulating valve and detector are bimetal, the detector shall be installed vertically on the butt weld fittings.

 

 

In the automatic control of modern factories, the regulating valve is very important. By accepting the control signal output from the control unit, the process parameters such as medium flow, pressure, temperature, and liquid level can be changed. It can be said that the regulating valve is the last gate in the process loop. Therefore, how to select the regulating valve correctly to achieve the best control effect has become the most critical problem.