Valve for regulating the rate of flow, pressure, temperature, level and process parameters such as industrial automation and process control in the field. According to the control signals in the automation system automatically adjusts the valve opening, in order to achieve the regulation of media flow, pressure, temperature and level. The regulating valve is usually composed of two parts by the electric actuator or pneumatic actuator and valve. Straight trip through single seat type and through two two-seater, which has a large flow capacity, the imbalance do small and stable operation of the features, so often especially suitable for high flow, high pressure drop and leak a few occasions. Rotary are: V-shaped electric ball valve, electric butterfly valves, ventilation valve, eccentric butterfly valve. The flow capacity of Cv value is one of the main parameters of the control valve selection, valve flow capacity is defined as: when the control valve fully open the valve at both ends of the differential pressure is 0.1MPa, the fluid density is 1g/cm3 hour flow path is the number of the flow control valve, known as the flow capacity, also known as the flow coefficient Cv, in units of t / h, liquid Cv value calculated. According to the flow capacity of Cv value size look-up table, you can determine the valve nominal diameter DN. In the automatic control of the modern factory, the control valve plays a very important role in the production of these plants depends on the proper allocation of the flow of liquids and gases and control. These control whether the exchange of energy, a decrease in pressure or simple container feeding, need some final control elements to complete. The final control element can be considered to be the automatic control of the "physical". Regulator of the low-energy order of magnitude and the implementation of the flow of fluid between the control energy level, the final control elements to complete the necessary power amplification. 
 Valve flow characteristics 
 Control valve flow characteristics, under the conditions of the valves at both ends of the pressure remains constant, the relationship between the relative flow of the medium flows through the valve and its opening. Control valve flow characteristics are linear features, such as the percentage of properties and the parabolic nature of the three. Percentage of control valves and other features, valve linear characteristic, valve parabolic characteristics. 
 Significance of the three fluence characteristics are as follows: 
 (1) the percentage of properties (logarithmic) 
 The percentage of properties relative stroke and the relative flow is not a linear relationship between the units in each point in the trip itinerary changes caused by changes in flow and this flow is proportional to the flow percentage change is equal. The advantage is that traffic hours, traffic changes in the flow, the flow changes, which is different, with the same regulation accuracy. 
 (2) linear features (linear) 
 The relative stroke and the relative flow of the linear characteristic into a linear relationship. Units stroke caused by changes in flow rate change is constant. Flow, flow, the relative value of small changes, traffic hours, the flow of the relative value changes. 
 (3) parabolic characteristic 
 Flow changes in proportion to the trip two parties, generally in the middle of the linear and equal percentage characteristic features. 
 It can be seen from the analysis of these three characteristics, its adjust a performance perspective, to the percentage of properties for the optimal stability of its regulation, good regulating performance. Regulation performance than linear parabolic characteristic features, according to require different occasions, the selection of any flow characteristics. 
 (4) The flow coefficient Kv 
 Regulating valve flow coefficient Kv, the important parameters of the control valve, which reflects the ability, that is, the control valve through the fluid control valve capacity. Adjust the calculation of the valve flow coefficient Kv, can determine the selection of the caliber of the valve. To correct choice of the caliber of the valve must be correctly calculated regulating valve rated flow coefficient Kv value. Regulating valve rated flow coefficient Kv is defined as: under specified conditions, that is, both ends of the valve differential pressure of 10Pa, the fluid density of lg / cm, m / h or t / h traffic flows through the regulating valve rated travel number. 
 Installation and maintenance of the control valve 
 The regulating valve is very common and is particularly important in the industrial production control devices, it is working properly or not directly related to the normal production of the device or not. Now, with the regulating valve technology advances, and adjust the valve manufacturer and the form of many different functions, the following highlights the various types of control valves in the installation and before operation should be noted that common problems. 
 1, incoming inspection of the valve of the regulating valve installed in front of incoming inspection is a very important part to meet the design requirements to confirm the valve arrival. The valve of each of the technical requirements shall meet the design requirements, but check the following number in the incoming inspection should focus on content. 
 2, the valve body / valve specification of this element include: valve type, valve type, nominal diameter, seat size, spool type, flow characteristics, the leakage rate, body material, valve core material, seat material , CV values, sanitary valve standard grade size and form of the sealing surface, as long as the same content and design does not match should be the consent of the identification and recognition of the design. 
 3, the implementation of part of this content should check the executing agency model, type, in the form of action, spring range, gas pressure. 
 4, mainly the location of the input signal locator part of this content, air pressure, electrical and air source interface size and explosion-proof rating, including explosion-proof rating shall not be less than the design level requirements. 
 5, Annex valve design techniques require careful cleaning of the various accessories, such as filter valve, the valve position switch, solenoid valve, hand wheel, special tools. Inspection of the above content can clean, measuring instruments, view the nameplate and a dedicated detection means (such as the method of the flange and bolt material by spectral analysis to identify). 
 6, when the hydrostatic test pressure test and the spool valve body fully closed valve hydraulic test the valve leak test. Under normal circumstances, when the design pressure more than 10MPa control valve, the valve body must be the pressure of the withstand voltage test to test the body itself and the valve cover.