The check valve is a multifunctional (slow closing) check valve with a power device and a free-stroke coupler, which has both electric/manual valve opening, closing, and short-term throttling. The valve seat is an inclined, all-metal seal pair, The butterfly plate double-biased, flow-through element is equipped with a fluid guide and an oil pressure slow closing device, which can be divided into: fast/slow two-stage closing valve. It is a new type of multifunctional waterproof hammer and energy-saving product.
According to the structure, check valves can be divided into three types: lift check valves, swing check valves and butterfly check valves. Lift check valves can be divided into two types: vertical and horizontal. Swing check valves are divided into three types: single, double and multiple. The butterfly check valve is straight-through. The above-mentioned check valves can be divided into three types: threaded connection, flange connection and welding. The structure of a lift check valve is generally similar to that of a stop valve. Its valve flap moves up and down along the channel in a line, which is reliable in action, but has a large fluid resistance and is suitable for light and small diameter occasions. The lift check valve can be straight-through and vertical. Straight-through lift check valves generally can only be installed in horizontal pipelines, while vertical lift check valves are generally installed in vertical pipelines. The disc of the swing check valve rotates around the rotating shaft. According to the number of discs, the swing check valve can be divided into three types: single disc swing, double disc swing and multi disc swing. Single flap swing check valve is generally suitable for medium-caliber occasions. When single flap swing check valve is used for large-diameter pipelines, in order to reduce water hammer pressure, it is best to use a slow closing check valve that can reduce water hammer pressure. The double flap swing check valve is suitable for large and medium diameter pipelines. Wafer double flap swing check valve has a small structure and light weight, and is a fast-developing check valve; multi flap swing check valve is suitable for large-caliber pipelines. The structure of butterfly check valve is similar to butterfly valve. Its structure is simple, the flow resistance is small, and the water hammer pressure is also small.
The check valve can be widely used in petrochemical, metallurgical, electric power and urban water supply and drainage systems. When the water pump is started or normally stopped, it can also function as a "water valve" and "check valve"; the water pump suddenly loses power , When the pump is stopped in an accident, the valve can be closed automatically and orderly (two stages of fast/slow), which completely acts as a check valve to prevent backflow of water, prevent destructive water hammer, and ensure the safety of the pumping station.
Selection of power station control valve
In the thermoelectric industry, the operating conditions of control valves are quite special. Simply speaking, the electric power process is just a cycle of water and steam, but the selection of control valves in this process is simple and complicated. The simple is that the process medium is simple, with only water and steam. The complicated is that the temperature and pressure of water and steam fluctuate widely, which brings a series of problems such as flashing, cavitation, erosion, noise, and corrosion. But the first thing to consider is the safety and reliability of the control valve.
1. Feed water valve (main and attached boiler feed water valve, compound feed water regulating valve)
Control requirements: control the boiler water intake, ensure the steam evaporation, and maintain the boiler water level (the main and auxiliary boiler feedwater valve systems include two control valves, one for use when the boiler is started, and one for normal feedwater use.
Working condition: When the boiler starts, the valve pressure difference can reach 100-300 kg, the flow rate is small, the pressure difference is small during normal operation, the flow rate is large, and the flow rate adjustable ratio is 75:1 to 100:1. Valve requirements: WCB/WC9. The start valve in the double valve system requires cavitation resistance and a V-level closing level. For the composite feedwater valve, it is necessary to use characteristic valve trims to meet the needs of boiler startup and normal operation. Generally, the valve is selected as fault closed.
2. The minimum flow circulation valve of the boiler feed water pump
Control requirements: make the boiler feed water pump start and stop running safely, and eliminate the damage to the pump due to too small flow, increased temperature rise, and strong water cavitation. Old-fashioned power stations have the use of on-off type minimum flow control valves, as well as the use of mechanical pump automatic circulation valves.
Working conditions: The pressure drop is 160-350 kg, which is the valve with the largest pressure difference in the power station system, and the flow is 30% of the normal flow.
Valve requirements: anti-cavitation, anti-blocking structure, V-level sealing level, the valve works continuously when the pump starts and stops running, the valve is closed after the pump starts normally, and the valve is usually open in failure.
3. High and low heater traps (feed water heater drain, condensate water heater drain)
Control requirements: control the position of the condensate in the heater, discharge the condensate in time, discharge the high water level, and drain the normal water level.
Working conditions: saturated water, the control valve pressure difference between the heaters is generally 6-30 kg, and the last stage trap is directly connected to the condenser or deaerator. Valve requirements: anti-flashing erosion, V or VI level of sealing, the valve is usually open for failure.
4. Deaerator water level control valve
Control requirements: Provide flow to maintain the normal water level of the deaerator, and increase the water temperature by adding steam to eliminate gases dissolved in the water.
Working condition: The flow is small at the start-up stage, the pressure difference is large, and the temperature is large under normal conditions. The working condition is similar to the water supply valve.
Valve requirements: effective anti-cavitation at low flow.
5. Desuperheating valve (desuperheater)
Control requirements: Inject high-pressure water into the steam to make the steam temperature meet the control requirements.
Working conditions: water, large pressure difference. Valve requirements: various types: nozzle type, auxiliary atomization type, self-contained type and wafer type.
6. Temperature reducing valve (high and low pressure bypass valve)
Control requirements: adjust the high temperature and high pressure steam to a certain temperature and pressure steam, provide a bypass channel for the steam turbine, and the boiler can work independently of the steam turbine. Working conditions: high temperature and high pressure steam, valve requirements: resistance to thermal shock, noise reduction, and rapid response.
Electric control valve maintenance is divided into emergency maintenance, regular maintenance and predictive maintenance. Emergency maintenance is the maintenance when the electric control valve fails and cannot meet the process operation requirements. Regular maintenance usually includes daily maintenance and maintenance that is carried out simultaneously with process shutdown overhaul. Predictive maintenance is based on the analysis results of predictive maintenance, targeted maintenance of the electric control valve components. Emergency maintenance is the maintenance after the electric control valve fails, and the regular maintenance and predictive maintenance are the maintenance before the electric control valve fails.
(1) Daily inspection and maintenance of electric control valves include the following:
1. Eliminate stress. Various stresses caused by improper installation or combination. For example, the high temperature medium generates thermal stress, and the installation is tight. Imbalance of solid force causes stress and so on. The imbalance of stress acts on the electric control valve, deforming the valve stem and guide of the electric control valve, and cannot be correctly aligned with the valve seat, causing leakage and increased deterioration. Therefore, maintenance work to eliminate stress should be carried out in daily maintenance.
2. Remove rust and dirt. Frequently check whether there is rust, welding slag, dirt, etc. in the connecting pipeline of the electric control valve, and remove it in time after discovery. Because these dirt will cause the electric control valve spool and valve seat to wear and affect the normal operation of the electric control valve. Generally, filter devices such as filters can be installed in front of the electric control valve and cleaned regularly.
3. Check the electric control valve support. The electric control valve support makes the parts of the control valve in a position that is not affected by gravity. If the support is improper, the valve stem of the electric control valve cannot be aligned with the valve seat, which increases the deterioration and reduces the sealing performance. Therefore, it should be checked whether the electric control valve support is suitable.
4. Remove the dirt that supplies energy such as air source and hydraulic oil. Air source and hydraulic source are the energy source for the operation of the electric control valve. Impurities contained in the instrument compressed air and hydraulic oil can block the orifice and pipes, causing malfunctions. Therefore, it is very important to check the air source and hydraulic oil regularly, and to drain the filter device regularly.
5. Inspection of gear transmission. The gear transmissions of the hand-wheel mechanism, electric actuator and hydraulic actuator should be checked regularly and lubricants should be added to prevent seizure. Check whether the brake and limit device are flexible and easy to use.
(2) The main contents of daily maintenance of electric control valves and accessories are as follows:
1. Replacement of diaphragm of pneumatic actuator. The diaphragm of the pneumatic film actuator is stretched during operation, so it is easy to fatigue and damage. The rubber diaphragm of the same specification should be used for replacement, and the diaphragm should be evenly stressed during tightening to prevent leakage and crushing of the diaphragm.
2. Grinding. The valve core and the valve seat cause leakage after a certain period of operation, and the internal leakage between the piston and the cylinder body of the cylinder will also cause internal leakage. At this time, grinding should be carried out. Hand-grinding, mechanical grinding, coating treatment and inserting can be carried out. The emery grain size used for grinding should be suitable, and the grinding force should be uniform and suitable. After grinding, it should be polished to meet the required finish and precision requirements, and to meet the centering requirements of the valve core and valve seat. After the final assembly, the electric control valve should be tested for tightness.
3. Replace the stuffing box. . The stuffing box of the same type should be used when replacing the stuffing box. When replacing the stuffing box, you should carefully hook the stuffing out and remove the stuffing correctly to prevent damage to the valve stem. The installation of the new stuffing box should be in accordance with the requirements of the manual. The incision should be misplaced to prevent the thread of the valve stem from scratching the packing. The packing should be evenly pressed against stress and increase friction.
4. Replacement of transmission parts. The electric control valve and the transmission parts in the accessories can be replaced and repaired if part of them is worn out. After replacement and repair, the transmission should be flexible and the transmission gap should be as small as possible.
In terms of operating efficiency and saving energy consumption, the use of automatic control valves is an indispensable part. The manual valves and pneumatic valves commonly used in traditional industries are not as good as electric valves in terms of installation cost and efficiency.
Relevant persons in the industry said that valves are mostly used in industrial processes to control the travel and flow of various fluids, such as water, oil, and chemical liquids, based on parameters such as temperature, pressure and flow. The control valves commonly used in factories include pressure reducing valves, pneumatic constant temperature valves, solenoid valve constant temperature systems, proportional control valve constant temperature systems, and temperature control valves. When selecting various types of automatic valves, consideration should be given to factors such as the type of heat engine, the required accuracy, the quality of the control valve, the pressure drop, the flow rate and its structure, the failure rate, the credit of the manufacturer, and the after-sales service to achieve economical and practical purposes.
As far as the product itself is concerned, the electric valve has the advantages of easy assembly, low failure rate, and compliance with the industry's automation needs, making it a more cost-effective choice for the industry. Because the general traditional pneumatic valve is used, it is inevitable to have piping, solenoid valve and compressor to match, and the electric valve is driven by a motor, which is simple and easy to install, and the electric valve can be installed with the original automatic control circuit of the factory, which can save other the costing payment. In addition, the opening and closing of the motor drive is smoother, without the shortcomings of excessive momentary force, and the failure rate can be greatly reduced.
Many people think that electric valves are expensive and costly to use. In fact, it is not. If calculated as a whole, traditional valves have to be installed with many accessories and pipelines, and the price is not dominant. Instead, they have to bear more maintenance costs.