Contact Me
Control valve knowledge
First of all, let's have a brief understanding of the control valve. The control valve belongs to the control valve series. Its main function is to adjust the pressure, flow, temperature and other parameters of the medium. It is the final control element in the process loop. The control valve plays a very important role in the automation control of modern factories. The production of these factories depends on the correct distribution and control of flowing liquid and gas. These controls, whether energy exchange, pressure reduction or simple container charging, need the final control components to complete. The final control element can be regarded as the "physical energy" of automatic control. Between the low-energy level of the regulator and the high-energy level of the flow fluid control, the final control element completes the necessary power amplification. The control valve is the most widely used form of the final control element
Regulating valve
The regulating valve plays a role of variable resistance in the pipeline. It changes the turbulence of the process fluid or provides a pressure drop in the case of laminar flow. The pressure drop is caused by changing the valve resistance or "friction". This process of pressure reduction is often called throttling. For gas, it is close to isothermal adiabatic state, and the deviation depends on the non ideal degree of gas (Joule Thomson effect). In the case of liquid, the pressure is consumed by turbulence or viscous friction, both of which convert the pressure into heat energy, resulting in a slight increase in temperature.
Type of control valve
According to the stroke characteristics, the regulating valve can be divided into straight stroke and angular stroke. Straight stroke includes: single seat valve, double seat valve, sleeve valve, angle valve, three-way valve, diaphragm valve; angle stroke includes: butterfly valve, ball valve, eccentric rotary valve, full function ultra light control valve. The control valve can be divided into pneumatic control valve, electric control valve and hydraulic control valve according to the driving mode; it can be divided into regulation type, cut-off type and regulation cut-off type according to the regulation form; it can be divided into linear, equal percentage, parabola and quick opening according to the flow characteristics. The control valve is suitable for air, water, steam, various corrosive media, mud, oil and other media.
self-actuated regulator
Self operated control valve, also known as self operated control valve, is a kind of control valve that relies on the pressure and temperature of the medium flowing through the valve as energy to drive the valve to work automatically without external power supply and secondary instrument.
Application of self operated control valve
(1) the regulating valve belongs to the on-site instrument panel, the specified working temperature should be in the range of - 25 ~ 60 ℃, and the air humidity should be ≤ 95%. If it is installed outdoors or in a high temperature place, the measures of moisture-proof and temperature reduction should be adopted. In areas with seismic source, vibration source should be eliminated or vibration isolation countermeasures should be improved.
(2) the regulating valve should be installed vertically, and it can be tilted under special conditions. If the angle of squint is large or the weight of the regulating valve is large, the supporting plate of the valve should be lifted for maintenance.
(3) the pipeline for installing electric control valve generally does not have to be too high from the road or wood floor. When the height width ratio of the pipeline exceeds 2m, the service platform should be set as far as possible to facilitate the operator's wheel and maintenance.
(4) before the installation of the regulating valve, the pipeline shall be cleaned, and the wastes and welding through shall be removed. After installation, in order to avoid residue in the valve body, the gate valve should be cleaned again, that is, when entering the material, all the gate valves should be opened to prevent residue sticking. After using the handle tissue, it should be restored to the original neutral position.
(5) in order to make the self operated control valve in the case of common faults or maintenance, so that the processing process can be carried out again, the control valve needs to add bypass valve pipeline. In addition, it should be noted that the installation position of the electric control valve is in line with the requirements of the whole process of processing technology.
(6) the installation of part of the electrical equipment of the self operated control valve shall be carried out according to the relevant electrical equipment engineering construction regulations. If it is explosion-proof goods, the installation should be carried out according to the provisions of "standard for installation of electrical equipment in explosion risk site". For example, SBH type or other 6-core or 8-core rubber sheathed cables with a diameter of 11.3 mm are selected for on-site transmission lines. In application maintenance, it is forbidden to connect the power supply to open the meter cover for maintenance and pry the flameproof surface in flammable and explosive sites. In addition, it is not necessary to touch or scratch the flameproof surface during disassembly, and the original flameproof condition shall be changed after maintenance.
(7) after the reducer of the electric actuator is disassembled, pay attention to oil lubrication. Generally, it is not necessary to disassemble the low-speed motor for oil lubrication. After the assembly line, check whether the valve position is consistent with the valve opening indication.
Application of control valve
Single seat control valve
Small leakage, easy to achieve strict sealing and cut-off, for example, metal to metal hard seal, or metal to polytetrafluoroethylene or other composite material soft seal, the standard leakage is 0.0l% C (C is the rated flow coefficient).
The allowable pressure difference is small, for example, the allowable pressure difference of dnl00 valve is only 120kPa.
The flow capacity is small, for example, the flow capacity of dnl00 through valve is only 100.
Due to the large thrust of the fluid medium on the valve core, that is, the imbalance force is large, therefore, in the application of high pressure difference and large diameter, it is not suitable to use this kind of control valve.
In recent years, through control valve with cage structure has been widely used because of its advantages of simple maintenance and changing valve flow characteristics by changing valve seat. In order to reduce the influence of the unbalanced force on the valve core, the high thrust actuator can be used, the straight through double seat valve structure can be adopted, and the cage structure of the balanced valve core can also be adopted. The sliding piston ring lubricated with graphite is used between the upper part of the valve core and the cylinder body of the valve cage to seal between the valve core and the valve cage. The bonnet gasket and spiral gasket are also used to seal between the cage and the upper bonnet to ensure that the upstream high-pressure fluid will not enter the downstream low-pressure chamber. In addition, the fluid acts on the bottom and top of the valve core through the balance connection hole at the top of the valve core, which eliminates most of the static unbalanced force and has a certain damping effect, reducing the influence of vibration and other disturbances caused by fluid flow.