1, confirm the selection criteria

(1) process flow conditions: the name of fluid flow, the inlet and outlet pressure, differential pressure in normal working conditions, the valve is closed

Force, fluid temperature, density, viscosity, any suspension under the fluid, fiber, slurry, etc. Sometimes, respectively

The minimum flow, normal flow, maximum flow of various process conditions.

(2) adjust the instrument conditions: flow characteristic, the function form, adjusting the instrument output signal, the position feedback signal, etc.

(3) pipe connection conditions: nominal pressure and connection, pipe size, thickness, pipe material, etc

2, in the form of primary valve

According to the process conditions to choose the proper form of valve.

(1) the characteristic of medium

A, general fluid

B, high viscosity, containing suspended solids, such as fiber fluid

C, poisonous substance or expensive

D, corrosive fluid

(2) the process parameters

A, low pressure, small pressure difference and large flow

B, in the low voltage, large pressure difference

C, the part of the group and/or other conditions

(3) the requirement

A, turned off the seat leakage amount or close to cut off the switch type requirements

B, good stability maintenance is convenient

C, air defense, and low noise

D, light weight, small volume

3, again to determine the control valve type

(1), according to the calculation of Cv value, to determine the rated diameter and Cv value of regulating valve. According to the regulator's conditions of use, and

Considering the manufacturing precision of regulating valve, in accordance with the following condition for valve diameter and nominal Cv is selected, when the maximum flow,

Regulator of the biggest opening should not exceed 95% (for equal percentage flow) and 90% (for the linear flow characteristic); When is

Often, the regulating valve opening should be between 50% and 80%; When the minimum flow valve opening of not less than 10%.

(2), at the same time, according to the working pressure, medium temperature and medium characteristics to determine the valve body and trim material and stress level;

Decision is the normal temperature, high temperature, low temperature type, namely to the structure of the stuffing box, packing material, and whether you need bellows;

In addition, such as estimated more than 85 dba noise, is an alternate low noise control valves.

Determine the valve form at the same time, according to the power source, determine the types of actuators, according to the working pressure difference and seat closed differential pressure

To determine the number of the actuator (output or torque) and the form.

4, determine the regulator with the attachments

(1), according to the controller output signal to determine the types of valve positioner, specifications;

(2), data sheets or site requirements, determine the protection grade, specification of electrical accessories;

(3), some of the regulating valve, wearing a single acting actuator, spring range 20-100 kpa, accept 20-100 kpa letter

Number, but if the owner, design institute, also can not take the valve positioner, adjustment precision is much lower than with valve, of course

Gate locator.

(4), according to the data sheets or the owner site requirements, equipped with other regulating valve accessories.