Selection principle: Regulating valve used to regulate the flow of media, pressure and liquid level. According to adjust the position of the signal, the valve automatically control the opening, so as to achieve the media flow, pressure and liquid level adjustment. Regulating valve sub-electric control valve, pneumatic control valve and hydraulic control valve. Regulating valve by the electric actuator or pneumatic actuator and control valve of two parts. Control valves are usually divided into two kinds of direct-through single-seat control valve and through two-seat control valve, which has the ability to circulate large, unbalanced small and stable operation, it is usually particularly suitable for large flow, high pressure drop and leakage Less occasions. Flow capacity Cv is one of the main parameters to select the control valve, the control valve flow capacity is defined as: When the control valve is fully open, the pressure drop across the valve is 0.1MPa, the fluid density of 1g / cm3 hourly flow path The number of flow control valve, known as the flow capacity, also known as flow coefficient, in Cv, said t / h, liquid Cv value calculated according to the following formula. According to the size of flow capacity Cv check the table, you can determine the nominal valve DN. Flow characteristics of the control valve, the pressure drop at both ends of the valve to maintain a constant condition, the medium flow through the control valve and the relative flow of its relationship between the opening. Regulating valve flow characteristics of linear characteristics, such as percentage characteristics and parabolic characteristics of three. Failure emergency treatment: 1. Cleaning method: pipe in the welding slag, rust, slag and other throttles in the throttle, guide parts, under the valve cover to balance the hole caused by blockage or stuck so that the valve surface, the guide surface tension and Scratches, seals and other surface indentation. This often occurs in the early delivery of new delivery systems and overhauls. This is the most common failure. In this case, you must uninstall the cleaning, remove the slag material, such as the sealing surface is also damaged should be ground; at the same time the bottom plug open to flush away from the balance hole into the valve cap slag material, and the pipeline Rinse. Put into operation before the valve is fully open, medium flow into the normal operation after a period of time. 2. External scour method: For some easy to sediment, the medium containing solid particles using ordinary valve adjustment, often in the throttle, the guide block, can be flush at the bottom of the valve cover bottom flushing gas and steam. When the valve is clogged or stuck, open the external gas or steam valve, you can complete the flushing work in the case of the valve does not move, so that the valve normal operation. 3. Installation of pipe filter method: The small-caliber control valve, especially the ultra-small flow control valve, the throttle clearance is very small, medium can not have a little slag material. In this case of blockage, it is best to install a filter on the valve before the pipeline to ensure the smooth passage of media. Control valve with locator, locator is not working properly, the air passage choke plug is the most common failure. Therefore, with the locator work, you must handle the gas source, the usual approach is to install the air filter in front of the locator air line pressure reducing valve. 4. Increase the throttling gap method: If the medium of solid particles or pipe was washed away the welding slag and rust and other overcrowding caused by congestion, stuck and other failures, can be used to throttle large gap Throttling pieces - throttle area for the fenestration, the opening of the spool, sleeve, because of its throttle area rather than the distribution of the circle, the fault can be easily ruled out. If it is single, two-seater valve spool valve can be changed to the V-shaped spool, or into the sleeve valve. For example, a chemical plant often have a double-seat valve stuck, it is recommended to switch to sleeve valve, the problem was resolved immediately. 5. Medium scour method: The use of the media itself scouring energy, erosion and easy to take away sedimentation, easy to block things, thereby improving the valve anti-blocking function. Common methods are: â‘ closed for the flow of closed-type use; â‘¡ the use of streamlined body; â‘¢ the throttle placed in the erosion of the most powerful, using this method should pay attention to improve the erosion-resistant materials, parts erosion. 6. Straight to the angle method: Straight through the inverted S flow, flow path complex, upper and lower cavity dead zone, provides a place for precipitation of the medium. Angular connection, the medium flows through the elbow 90, erosion performance, small dead zone, easy to design streamlined. Therefore, the use of straight through the control valve can be slightly blocked when the valve can be changed to use. Actuator Description: In order to make the regulating valve work normally, the matching implementing agency should be able to generate sufficient output force to ensure a high degree of sealing and valve opening. For double-acting pneumatic, hydraulic, electric actuator, there is usually no return spring. The size of the force has nothing to do with its direction of operation, so the key to choosing an actuator lies in knowing the maximum output force and the torque of the motor. For single-acting pneumatic actuators, the output force is related to the opening of the valve, and the presence of force on the regulating valve will also affect the kinematic behavior, thus requiring a force balance across the opening of the regulating valve. After determining the output force of the implementing agency, select the appropriate implementing agency according to the process environment requirements. For on-site explosion-proof requirements, pneumatic actuators should be used. From the energy-saving aspects, should try to use electric actuator. If the adjustment of high precision, hydraulic actuator can choose. Such as power plant transparent speed control, refinery catalytic reactor temperature control and so on. The role of the control valve is only used in the selection of pneumatic actuators, and its role in the positive and negative through the implementing agencies and the positive and negative valve action combination. There are four types of combination that is positive (air-off type), positive and negative (air-open type), anyway (air-open type), anti-anti (anti-off type) Open and Qi off two. For the control valve mode of action, mainly from three aspects: 1, process safety; 2, the characteristics of the media; 3, to ensure product quality, economic loss is minimal.
Plunger metering pump, is characterized by the plunger reciprocating motion, which means: the working chamber of the pump liquid end is caused from the plunger, the pump will reach the quantitative dosing through the plunger reciprocating motion, the accuracy of this dosing will be + 1%. The resistant piston in the heart of liquid end of a plunger pump is coated with stainless steel, the operation theory is: when the plunger is moved into the dosing head, the suction valve closes and the feed chemical flows out of the dosing head through a discharge valve. When the plunger moves in the opposite direction, the discharge valve closes due to the negative pressure in the dosing head. Fresh feed chemical flows through the suction valve into the dosing head. The plunger metering pump usually used in chemical and petrochemical, pharmaceutical, cosmetic and food production industry. However, there are different control types which make easy process integration.
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