Valve is a device used to control the flow of fluids (such as liquid, gas, steam, etc.) by changing the cross-sectional area of its internal channel to adjust the flow, pressure and direction of the fluid. Valves can be manually operated or automatically controlled to suit different industrial and engineering needs.
Function:
- Opening and closing action: cut off or communicate the flow of fluid in the tube. Adjustment function: Adjust the flow and velocity in the pipe.
- Throttling action: Pressure drop is generated after the fluid passes through the valve.
- Safety role: such as safety valve, used for overpressure protection, to prevent equipment or pipeline system due to high pressure damage.
- Check action: prevents the reverse flow of fluid, such as a check valve.
- Diverting action: Distributing fluid to different pipes or collecting fluid in multiple pipes.
Classification by use:
- Cut-off valve: used to cut off or connect the medium flow, such as gate valve, globe valve, ball valve, butterfly valve, plug valve, etc.
- Regulating valve: used to regulate the flow, pressure, etc., such as regulating valve, throttle valve, pressure reducing valve, etc.
- Check valve: used to prevent the backflow of the medium, such as lifting check valve, swing check valve, etc.
- Diverter valve: used for separating, distributing or mixing media, such as distributing valves and traps.
- Safety valve: used for medium overpressure safety protection, such as spring type safety valve, lever type safety valve, etc.
By drive type:
- Manual valves: Operated by manual devices such as hand wheels, levers or sprockets. Electric valve: Remote control via electric actuator.
- Pneumatic valve: Use compressed air to drive the actuator.
- Hydraulic valve: The actuator is driven by hydraulic pressure.
- Solenoid valve: driven by a magnetic force generated by an electromagnetic coil.
Classification by valve body structure:
- Straight through valve: The channel of fluid through the valve is consistent with the pipeline axis, such as gate valve and stop valve.
- Three-way valve: The fluid can be divided or combined after passing through the valve, such as a three-way valve.
- Angle valve: The direction of the fluid changes when it passes through the valve, usually used to change the flow direction.
Classified by sealing surface:
- Soft seal valve: the sealing surface is made of rubber, polytetrafluoroethylene and other soft materials.
- Hard sealing valve: the sealing surface is made of metal or other hard materials.
Classified by pressure:
- Low pressure valve: suitable for low pressure occasions.
- Medium pressure valve: suitable for medium pressure occasions.
- High pressure valve: Suitable for high pressure system.
- Ultra-high pressure valves: Suitable for systems that exceed the standard high pressure range.
Classification by temperature:
- Normal temperature valve: suitable for medium not exceeding 100℃.
- Medium temperature valve: suitable for 100℃ to 450℃ medium.
- High temperature valve: suitable for medium above 450℃.
By connection type:
- Flanged valves: connected to pipes through flanges.
- Threaded valve: threaded to pipe connection.
- Welded valves: welded to pipes.
How to choose the valve?
- Clear valve use: First of all to determine the role of the valve in the system, such as truncation, adjustment, check, safe release and so on. 2) Fluid characteristics: Consider the corrosion of the medium, temperature, pressure, viscosity and whether it contains solid particles. 3) Valve performance parameters: Select the appropriate valve according to the required flow rate, pressure drop, sealing requirements and other parameters. 4) Process requirements: consider the special needs in the process, such as anti-corrosion, fire prevention, explosion-proof, etc. 5) Safety: Ensure that the valve can work safely under abnormal conditions, such as through the safety valve to prevent high pressure. 6) Material selection: Select the right material according to the medium and working conditions, such as cast iron, stainless steel, plastic, etc. 7) Operation mode: Determine the operation mode of the valve, such as manual, electric, pneumatic or hydraulic. 8) Maintenance and cost: Consider the maintenance convenience and cost effectiveness of the valve, choose a valve that is easy to maintain and reasonable in cost. 9) Environmental factors: consider the temperature, humidity, vibration and other conditions of the installation environment. 10) Compliance: Ensure that the selected valve meets the relevant industry standards and regulatory requirements.
General valve selection criteria: ball valve is suitable for quick opening and closing and regulating flow, butterfly valve is suitable for large flow control, gate valve is suitable for occasions requiring low flow resistance, check valve is used to prevent media backflow, safety valve is used for pressure release. Each valve type has its specific application scenarios and advantages, and choosing the right valve can improve system efficiency, reduce energy consumption, and ensure safe operation.
How to install valves?
- The position of the valve installation should not hinder the operation, disassembly and maintenance of the equipment, pipes and valve body itself, while taking into account the aesthetic appearance of the assembly. 2) The valve on the horizontal pipeline, the valve stem is installed upward, or the installation is tilted at a certain Angle, and the handwheel cannot be installed downward. The valve, stem and handwheel on the high-altitude pipe can be installed horizontally, and the valve is opened and closed remotely by a low vertical chain. 3) Symmetrical arrangement, neat and beautiful; The valve on the riser, under the premise of the process permits, the valve handwheel is most suitable for operation at chest height, generally 1.0-1.2m from the ground, and the valve stem must be installed along the direction of the operator. 4) The valve on the side-by-side riser, its center line elevation is best consistent, and the net distance between the handwheels is not less than 100mm; Valves on side-by-side horizontal pipes should be staggered to reduce pipe spacing. 5) When installing heavy valves on pumps, heat exchangers and other equipment, valve brackets should be set up; When the valve is frequently operated and installed more than 1.8m away from the operating surface, a fixed operating platform should be set up. 6) The valve body is marked by an arrow, and the arrow points to the direction of the flow of the medium. When installing the valve, be careful to make the arrow point the same as the medium flow in the pipeline. 7) When installing the flange valve, it should be ensured that the end faces of the two flanges are parallel and concentric, and double gaskets should not be used. 8) When installing the threaded valve, in order to facilitate disassembly, a threaded valve should be equipped with a loose joint. The setup of the connector should consider the convenience of maintenance, usually the water flow first through the valve and then through the connector.
Maintaining:
- The valve should be stored in a dry and ventilated indoor environment, and both ends of the passage should be blocked. Check the valve regularly, remove dirt, and apply anti-rust oil on the processing surface. Check the wear of the sealing surface, the wear of the valve stem thread, and whether the packing is outdated and ineffective. If there is damage, it should be replaced in time. After the valve repair and assembly, the sealing performance test should be carried out. 2) When the valve grease, attention should be paid to the amount of grease injection, neither insufficient fat injection leading to wear of the sealing surface, nor excessive fat injection causing waste. Grease injection pressure should be appropriate, too high or too low will affect the valve performance. The valve should be in the correct switching position when the grease is injected to ensure that the grease can be evenly distributed. 3) Regularly check the transmission parts of the valve, such as valve stem threads, and add lubricating oil to reduce wear. Check whether the valve operating device is flexible and accurate, and repair or replace abnormal parts in time. Check whether the electric head and its transmission mechanism have water problems, especially in the rainy season, to prevent rust and freezing. 4) The packing is the key seal of the valve, and its sealing performance should be checked regularly and the damaged or aging packing should be replaced in time. After the valve is loaded into the pipeline, due to the temperature change may occur extravseepage, should be tightened in time on both sides of the packing gland nuts. 5) According to the type of valve and use conditions, set a reasonable maintenance cycle, such as quarterly or semi-annual maintenance.
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